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View Full Version : Burnham MPO-IQ versus Buderus G125BE Oil Boilers



danboston
03-29-2011, 03:34 PM
I have decided to replace my 50-Year old American Standard oil boiler (tankless coil) with a new oil-fired unit. Four adults live in a 1,700 ft2 ranch with 1,500 ft2 basement. We have 145 feet total length of Al-fin baseboard heating, all on the ground floor. I will be adding baseboard heating to the basement in the future. A heat loss calculation indicates a 90,000 btu/hr rate for the house.

I am contemplating either the Burnham MPO-IQ115 with an ouput of 98,000 btu/hr or the Buderus G125BE/28 with an output of 97,000 btu/hr. Both of these are cast-iron boilers, with an AFUE rating of 86% for the Burnham MPO-IQ and 90% AFUE rating for the Buderus G125BE. The Burnham MPO-IQ apparently comes standard with an outdoor temperature control that adjusts the boiler water temperature based upon outdoor temperatures. Buderus supplies a similar control (Logamatic 2107) as an add-on for additional cost. The Buderus goes one step further and offers a condensing mode option as well (as a side note, I live about 10 miles from the Buderus headquarters in Londonderry, NH).

If I go with the Burnham, I also plan to get a Burnham Alliance 50-gallon stone-lined indirect water heater. The contractor told me that the water in my area is not so great and not good for a stainless steel water heater therefore he recommended the stone-lined tank. If I go with the Buderus, I would likely get the Buderus Logalux LT-200, which is a 53 gallon indirect water heater. Its not clear to me what Buderus uses I believe it is stainless steel. But I also heard that stainless steel made in the US is not up to par with stainless steel made in Europe?

Anyone have any experience (good or bad) with either of these models? I heard that Burnham has had issues with the cast iron boilers cracking? Any recommendations regarding options with the Buderus (are they worth the additional cost)?

Dana
03-30-2011, 08:38 AM
FWIW: Unless you live in the leakiest uninsulated house in Andover or have more glazed area than code allows, that 90K number is almost certainly 2x reality. (My measured heat load at 0F design temp on a circa 1923 ~2000' house + ~1500' of semi-conditioned basement in Worcester is ~30K, and that's with less than R20 in a significant fraction of cathedralized roof in the attic rooms, and a few known gaps in the wall insulation.) Getting rid of the cast iron beast and using a gas-fired tankless HW heater as a boiler + buffer tank I've been able to trim the output downward and modulate with load somewhat. With all zones calling for heat it doesn't put out more than ~42K (needed to bump up the temp for exit air comfort on a hydro-air zone, or I'd back it off even more), and it keeps up just fine, even cycles at -10F, so I'm pretty confident of the actual heat load. Prior to insulating the basement walls, foundation sill & band joist , pounding some cellulose into the 2x4 cavites where it was easy, and the heat load was closer to 43-45K, based on fuel-use history rated against heating degree-day data.

If you have accurate fuel use data on your existing system you can use that (and the boiler's specs) to get a fairly accurate heat load measurement using the FSA tool downloadable from a link on this page (http://www.nora-oilheat.org/site20/index.mv?screen=home).

OTOH, the smallest oil burners are still likely to be 2x oversized for your actual load too, and if you're multi-zoning it with low-mass emitters such as baseboard, the individual zones will be a tiny fraction of the boiler output and you'll have to buffer it to keep it from short-cycling itself into lower efficiency and higher maintenance. If you can figure out what your actual design day water temperature needs are (I't take a WAG at ~140F, which is the min-temp of the return water for a cast-iron oil boiler) it may make sense to use a buffer-centric approach using a reverse-indirect rather than a standard indirect (Everhot EA-series, TurboMax, or Ergomax), with the boiler slaved to the aquastat on the boiler as it's only zone, with the zones sipping from the reverse-indirect/buffer, like this:

http://www.ergomax.com/Radiant.jpg

That way there's a minimum burn time determined by the mass of the buffer/indirect- it can't short-cycle, and the water temp or room temp doesn't need a huge hysteresis to keep the boiler from short-cycling. Under long hot water draws the boiler kicks and it'll deliver pretty much a full shower flow continuously, and has the mass of the tank to back it up a bit. If you set the tank's aquastat to about the design day heating water requirement, it'll probably be a reasonable temp for the DHW load as well, but you'll still have to install an thermostatic mixing valve at the DHW output should you ever need/want to crank the tank temp higher.

I've read bloggery in recent years that the fuel availble in the US isn't really up to snuff for running a condensing Buderus- I'd research that a lot closer before going that route. Their non-condensing models have a good rep.

Given that oil demand worldwide looks like demand will continue to increase faster than supply for at least a decade prices on heating oil are likely to continue to be very volatile. With the Allegheny shale gas now coming on line, the future for natural gas in New England are likely to be both more stable and continue to be much lower per BTU- if you're anywhere near the local gas grid (http://www.columbiagasma.com/en/about-us/service-area.aspx), this might be the time to switch fuels, and you'd have quite an array of modulating/condensing options (in which case you might NOT want to use a buffer-centric system architecture.)

Last, not least, if it's not too late, DO insulate your basement walls before finishing it out, and do it in such a way that you don't create a mold/rot problem. See:


http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis (http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis)

I did mine at ~R20 using recycled 3" semi-permeable rigid iso, but 2-3" of EPS and unfaced batts in a studwall, no interior vapor barrier gets you there too. Recycled rigid board goods can be had on the cheap locally in Framingham at The Insulation Depot (http://www.insulationdepot.com/). Unless you know for certain that you have a capillary break at the foundation sill, don't use any foil-faced rigid-board, and if you use XPS (pink/blue) you can't go more than 2" before it cuts the drying capacity of the foundation too much. You can put up to 4" (~R16) of un-faced EPS though. With an all-foam-board approach you can hold it in place with furring through-screwed into the foundation with tap-cons and hang the gypsum on the furring. If you have a fieldstone foundation 2" of closed cell foam + unfaced batts in a studwall are probably the better approach. Set the studall up first, and make sure the foam seals up to the stud edges before adding the batts. Put 6mil poly under the floor plate of the studwall as a capillary break.

danboston
03-30-2011, 11:16 AM
Dana:

I feel that the house is well insulated. We had treated cellulose blown into the wall cavities, as well as, 8" in the attic. We also replaced all the windows, including the basement with Andersen 400-Series windows. As I mentioned, it is a small ranch (the square footage of the ground floor is 1,700 ft2 and the basement area is 1,500 ft2). I am currently insulating the basement as well (the basement will have dri-core panels on the floor, R-13 foamboard on the walls, and R-30 fiberglass batts in the ceiling). We will add some additional baseboard heating elements to the basement as an additional zone in the next year.

The house is currently heated with a circa 1950's tankless American Standard oil boiler (Arcoliner 3B J3 series) and a forced hot water Mono Flo baseboard aluminum fin system on two zones. The total length of the baseboard emitters is 145 feet and they are all on the ground floor. There are currently no heating elements in the basement. The tankless coil boiler provides all the heat and hot water for the house. We currently run out of hot water quickly if two showers are taken back-to-back or if the forced hot water heating system kicks on when in the shower.

In 2010, we burned 720 gallons of oil. The total number of heating degree days in 2010 for our area totalled 5,778. If I did this correct, this yields a K-factor of 8 (5,778/720). I tried the NORA Fuel Savings Analysis (FSA) calculator and under Step 2 it gave me a design day heat load of about 30,000 btu/hr when I input Boston, MA as the location, design temperature of -2 F and a K-factor of 8.

I would like to switch to gas, unfortunately the gas company wants to charge me $6,200 to move the gas main in front of my house. That is a dilemma since I am convinced that oil prices will continue to rise at a much greater clip than natural gas. I may bite the bullet and just do it. But that leads to the question then of what type of gas-fired boiler is best for my low-mass baseboard system?

I had a contractor come by and he told me that since we have a Mono-Flo baseboard heating system with aluminum fins (not cast iron), then he does not recommend a gas-fired high-efficiency mod-con boiler. The main reason being that the return water ends up being too hot and therefore the boiler will never have a chance to enter into condensing mode. If we had cast-iron fins, or a radiant heating system, then he said that is a much better situation for a mod-con boiler since the return water ends up being much cooler. Therefore, he recommended either a conventional gas-fired or oil-fired boiler (both Burnhams).

I provided the contractor with information about room, door and windows sizes, insulation, etc. and he had a Heat Loss calculation done for me. That indicated a Heat Loss of about 90,000 btu/hr (I can send that to you as part of a PM if you would be willing to review it for me – that would be much appreciated). Obviously 30,000 but/hr is substantially different than 90,000 btu/hr. Something is not right there.

Dana
03-30-2011, 01:33 PM
Dri-Core has no appreciable R value, and with ~50F subsoil temps the heat loss out the slab will be signficant- well worth putting down a couple inches (R8) of EPS under a floating tap-conned OSB or plywood subfloor. (Or at a minimum 1" of XPS sheathing for R5). The prescriptive conservation code for new construction in MA is for R10 sub-slab, but in retrofits you can run out of headroom. R5 is WAY better than R0.5 (the probable R value of Dri-Core), and would protect rugs from developing mold on the underside by keeping it well above the dew point of the interior air despite the R1-2 of the rug itself. See: http://energycode.pnl.gov/EnergyCodeReqs/?state=Massachusetts

You simply can't have a design day heat load that would indicate 2x the BTU content of the fuel you heated the house with, eh? ;-) I you used 720 x 139000=100.08MBTU in 5778 heating degree days, that's 17321BTU/HDD, or 722 BTU per heating degree-hour. Assuming a design temp of -2F (which is probably below the ASHRAE 99% binned hourly value) and an interior design temp of 68F, that's a 70 degree delta. 70 x 722= 50.5KBTU/hr of SOURCE fuel energy, with no discounting for boiler efficiency or hot water use! Assuming 20-25% of that is hot water use (likely, with an embedded coil- see: http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf ) only 38-40K of source-fuel was devoted to space heating (less than half the 90K number), and assuming 80% efficiency on the old boiler, that puts you again right at about 30-32K for a whole house design day heat load, not more. I'm buying the NORA-model calculated number much more than the contractor's calculated number. If your 60 year old boiler is running under 80% (which it might be), your design day heat load is even lower.

Mod con boilers can work just fine with fin tube baseboard, provided you don't oversize the boiler (the min-modulated output is more important than the max). But again, it's the amount of emitter in the smallest zone and the output of the boiler at minimum fire that determines whether it'll short-cyle without adding mass. But it's both cheap and EASY to add mass when needed by inserting a buffer tank (a small electric HW heater that isn't hooked up to power does nicely.) With fin-tube the min temp at which it has predictable output is ~110-120F, but that's plenty low enough to put the system in the mid-90s for efficiency.

Flat panel radiators or cast-iron baseboard can run predicably even below 90F, but it's sometimes a lot to pay for another 3% of efficiency (but there is an enhanced comfort-factor as well.)

Embedded hot water coils in boilers are notoriously low capacity when new, and drop significantly over time as they lime up. In my kludged up system I can run a shower literally all day long, but that's with a "free" kickback of 20-30K coming back from a drainwater heat exchanger on the cold-feed into the reverse-indirect. The boiler's output eventually hits ~50K on long showers (10 to 15+ minutes) as it draws the tank temp down to ~108F, causing the tankless water heater I'm using for a boiler to smoothly increase it's output. With a mod-con you'd get better results with a standard indirect sized for the number of users and the boiler's output, controlling the indirect as the "priority zone". At 30K of heat load you can use the smallest mod-cons out there, that modulated from ~15K to 50K, but with 4 showering adults and a 50K-max burner you'll want more than a 30 gallon indirect.

It's often cheaper/better to go with a gas-fired combi system based on a tank type hot water heater (condensing or otherwise) when your design day heat loads are under 25K, which they might be after you've insulated the basement. If your design-day heating water temp requirement based on the amount of fin-tube is 140F or less, it's nearly ideal, as long as it has enough burner. The nicer ones are like the HTP VERSA (http://www.htproducts.com/versa-hydro.html), which has a modulating burner to handle the much higher peak hot-water heating loads (2-3x your peak space heating load.), but there are cheaper versions like the B-W Combi-2 (http://www.bradfordwhite.com/images/shared/pdfs/specsheets/557B.pdf). They're inherently high-mass, and literally can't short-cycle on zone calls no matter how finely you chop it up, and easier to design around than a mod-con. The Versa has a bigger burner than the Combi-2, and would have more margin for hot-water heating even if you went with the smallest version, but the Combi-2 plus a ~50% efficiency drainwater heat exchanger (http://www.efi.org/wholesale/pdfs/power_pipe.pdf) would still give you the hot-water heating output you need for multiple back-to-back showers with plenty of overhead for a 30K design space heating load.

Dana
03-30-2011, 01:59 PM
If it only cost six grand to bring gas to the house, consider that part of the cost of the new heating system. It's a serious cost adder, but if you used only 720gallons of oil with a wheezing 1950s oil boiler, a right-sized cast iron or a low mass mod-con supporting those loads will use at most about 1000 therms/year. I'm not sure what your gas rates are (it's a different supplier than mine), but the most I've EVER paid was ~$1.50/therm, and in the past couple of years it's been in the ~$1-1.25 range. Even if it hit $1.50 again (probably will, if there's a rapid economic recovery) that's only ~$1500/year. With a better-efficiency oil boiler you might drop to 600 gallons/ year, but probably not 500, but even at 500 gallons/year, assuming it averages $3.50/gallon for the next decade rather than the current $4 that's still an annual savings of $250. A decade from now I'd expect gas to be a bit higher, but oil to be MUCH higher.

Predicting future prices in the short & medium term is a sucker game played out in the futures markets daily, and the decade-out guesses have many ways to fail, but unless people in India and China stop buying cars or the price of electric cars falls through the floor, the price-pressure on oil is going to be even more severe in 2020 than it is today. In 2010 more cars were sold in China than the US, and team USA's total share of the world oil consumption edged toward 20%, down from 30% 25 years ago. By 2020 we'll no longer be the consumer tail wagging the world oil price dog the way we have been, and the fraction of diesel (which competes for the same barrel-fraction as heating oil) is continuing on a rapid upswing that began in Europe in the 1990s. That $6K investment now might look pretty good.

danboston
03-30-2011, 03:24 PM
Dana: Your heat load calcualtion makes perfect sense. Thanks!

I will scrap the dri-core idea and apply foil-faced DOW TUFF-R 2-inch polyisocyanurate foam boards to the floor and cover with floating 1/2" exposure 1 rated plywood. I'll use tapcon screws to secure to the floor. The headroom in the basement is not an issue.

Ok, I have decided to take the plunge and am going with gas. I am leaning towards the Burnham Alpine 80, which modulates between 16 K btu/hr and 80 K btu/hr. However, I am concerned that the return water may be too warm for the boiler to enter into condensing mode on a regular basis. What are my options to ensure that the return water is cool enough so the boiler burns efficiently? The smallest zone has 40 feet of total emitters. For a proposed gas-fired mod-con setup, would the small unplugged electric water heater acting as a buffer go between the end of the return line and the return inlet to the boiler? That seems like a waste of heat - any way to capture that without spending a lot?

Finally, if I go with a unit like the Alpine 80, do I still need a 50-gal indirect water heater? There are 4 adults. The house will have two showers available. Plus I am installing a 70-gall jacuzzi. Only two of these would be running at the same time (i.e., two showers or 1 shower and 1 jacuzzi filling up).

danboston
03-30-2011, 03:28 PM
A Buderus contractor came by this morning to take a look. I told him that I wanted to go with gas and he recommended the Buderus wall hung model. When I told him my concern about the return water might be too warm for the boiler to enter into condensing mode on a regular basis, he looked a little stumped and said he would get back to me.

Dana
03-31-2011, 08:39 AM
DON'T use foil-faced iso on the floor- it's hygroscopic, and would eventually saturate with water reducing it's R value by half. It's mechanical pressure loading is also lower than most grades of XPS or EPS. Both EPS and XPS have a better closed-cell structure than iso, and while they too could take on water over time if fully submerged, they won't wick it in and hang onto it the way iso does. Whatever you use for foam, lap the seams between the plywood vs. the rigid board by a foot to avoid getting compression-rockering at the edges.

The Burnham Alpine is a decent boiler, as are the Buderus condensing boilers, and there are many others (Triangle-Tube Solo 60, Peerless Pinnacle T50, etc, etc.) The design & installation competence of the contractor and local support from distributors is more important than the manufacturers. These boilers come with a control setup called "outdoor reset", whereby the output temp of the boiler varies responds to the outdoor air temp as a rough model of the heat load. When it's warmer out, the temperature of the heating water drops, guaranteeing more condensing time. These response curves are programmable, typically with settable min temps (useful for fin-tube, which is has a very non-linear output curve at lower temps compared to radiators or radiant floor), and have to be tweaked as part of commissioning of the boiler.

With 2 showers running you'll need a 50 gallon indirect. The max output of the -80 in water heating mode will be ~75K, which is enough to support one 2-2.5gpm flow, but not two. It's about right for filling the jacuzzi, but if the person stays in the shower for a long time or the fill rate of the Jacuzzi is too fast the person in the shower could end up with tepid water toward the end.

As long as the buffer tank is inside conditioned space, any "loss" is to the conditioned space, lowering the heat load. But since electric tanks are well insulated, the rate of loss is pretty slow, and won't much affect the temperature of the room it's in. What the buffer saves is wear & tear on the boiler, and preserves the efficiency of the boiler, since there is a fixed loss on every burn due to ignition cycles and flue purges. Ideally it would be set up with minimum burns in excess of 10minutes under all heat load conditions. The thermal mass of fin tube is low- about a gallon every 50', so you're looking at a whole-system of only 3-4 gallons, maybe 30-35lbs of water. Assuming a temperature hysterisis of even 10F, it takes at most 35 x 10= 350 BTUs to raise the temp that 20F, and at the minimum fire of the Alpine in condensing mode you're looking at ~15KBTU/hr it takes less than 1.5 minutes to achieve that rise, and that's with ALL ZONES RUNNING. With 30 gallons of buffer that's more like 15 minutes.

There are variations on how buffers can be configured in the system, and it depends somewhat on the zoning & pumping/valving schemes that will be necessary- it's a design issue that needs to be addressed by the competent contractor, since it may vary with how big the zones are, and the flow requirements of the boiler (which will differ with manufacturer and model. But with an indirect and a few zones, setting it up as the point of hydraulic seperation in a primary/secondary is a bulletproof approach:

http://www.radiantandhydronics.com/RH/Home/Images/0509rh-GF-Fix-lg.jpg

which is similar to;

http://www.pmengineer.com/SHT/Home/Images/PME_0907_Feat2Fig10Lg.jpg

(but here the buffer tank has 4 connections rather than external Tees)

In simple systems it's sometimes easier to put the buffer in series with the boiler either the output or returns manifolds from which the zones are drawing, and put the indirect on it's own local loop. The indirect is self-buffering with plenty of thermal mass, the key is to get the mass of the buffer involved with every space-heating burn, independent of the size & mass of the zone that's calling for heat.

While this is something the contractor should be competent to design, correctly spelling "plumbing and heating" on the side of the truck is no guarantee of anything. Ask questions, get multiple proposals.

There should have been no confusion for the guy selling the contractor proposing the Budurus, who should have been able to tell you without looking it up or doing the math that you can run in condensing mode most of the time, even with fin-tube in a house with 145' of fin-tube and a 30K design day heat load. Literally 99% of the time the load is under 30K and the bulk of the fuel burned will be at heat loads under half that. Considering that 145' of fin tube can deliver about 40-45K at 140F, odds are good that it can be set up to be in condensing mode even during design conditions. It puts a question mark over the design competence.

Similarly, anybody who would hand you a heat-load calc so OBVIOUSLY wrong for the house without batting an eye isn't someone I'd trust the system design to.

But the guy in the truck isn't always the hydronic designer- find out who is, and work the details with THEM. One way to find the competent contractors serving your area is to get a recommendation from the boiler distributor- THEY know who's always bugging them with inanne support questions, and who is installing a lot of a particular line with few returns and minimal support. Hydronic design isn't rocket science, but you DO have to run the math- it's not just plumbing hook-up problem.

danboston
03-31-2011, 11:34 AM
Thanks Dana.

Is it Ok to use the polyisocyanurate boards on the walls? The local Building inspector wants us to use a vapor barrier so I glued foil-faced polyisocyanurate boards on the walls instead of plastic sheeting on a wooden frame for fear of moisture buildup and eventual rot of the wood frame. I was going to leave a 1-inch gap between the polyiso boards and the wood frame to prevent condensation water that is likely to form on the polyiso boards in the warm months from contacting directly with the wood frame. I do not have a moisture block between the top of the foundation and the sill, but I think I am going to have to live with it. I live on a nice dry hill and have never had water in the basement - just moisture issues in the summer months that is controlled with a dehumidifier.

Good recommendation about talking with the designer. The person who did the heat calcs is the contractor's distributor. I asked the contractor if I should send along information about actual fuel use and the HDD numbers and he said that he would not need those. I do have the distributor's contact information, I will just have to figure out the best way to get that information to the distributor without torquing off the contractor...

jadnashua
03-31-2011, 01:56 PM
The absolute best way to determine how much heat you need is to compare it to what you used to make the house comfortable (to you) and then assess it to the outside conditions during that time. Anything else has some assumptions, which are often wrong, oversizing the unit. It's okay to give it a little fudge factor. One thing to keep in mind is that the house won't magically become an icebox if it is a little small...it just will drop back a few degrees on those really cold days. Say, you design it for 0-degrees, and were 'perfect' in yous assessment. Then, it gets to -1. The house would gradually cool off that one degree from your preferred setting, and then only after it had been there for awhile (depending on the insulation levels). Then, when the sun comes back out, it will warm back up. Where you need, or probably want, some excess, is if say the house was vacant for a long weekend, and you then turned up the thermostat when you got home. Without some extra, it would be quite slow to recover. Now, some of this is a function of how much radiator capability you have, but obviously, some is a function of how much heat you can provide to them as well. You'll be far more comfortable with the boiler running at the right temp all the time, with the radiators just providing the necessary heat to maintain your desired set point rather than running at full hot for a few minutes, then cooling off and then starting all over. The system will be more efficient and last longer, too.

There are too many contractors that either can't or won't make the proper calculations, resulting in inefficient systems. It used to be the norm to have a system way oversized since energy was cheap. Many are taking the lazy way out and using 'rules of thumb' to determine what is needed (like 145' of radiators needs x sized boiler). This almost always means that the system is oversized, but that you won't come back to them and say the system can't keep the house warm (since it has way more capability than needed).

Dana
03-31-2011, 02:16 PM
Thanks Dana.

Is it Ok to use the polyisocyanurate boards on the walls? The local Building inspector wants us to use a vapor barrier so I glued foil-faced polyisocyanurate boards on the walls instead of plastic sheeting on a wooden frame for fear of moisture buildup and eventual rot of the wood frame. I was going to leave a 1-inch gap between the polyiso boards and the wood frame to prevent condensation water that is likely to form on the polyiso boards in the warm months from contacting directly with the wood frame. I do not have a moisture block between the top of the foundation and the sill, but I think I am going to have to live with it. I live on a nice dry hill and have never had water in the basement - just moisture issues in the summer months that is controlled with a dehumidifier.

Good recommendation about talking with the designer. The person who did the heat calcs is the contractor's distributor. I asked the contractor if I should send along information about actual fuel use and the HDD numbers and he said that he would not need those. I do have the distributor's contact information, I will just have to figure out the best way to get that information to the distributor without torquing off the contractor...


Foil faced iso on the walls is somewhat risky, since it raises the moisture content of the concrete from ground moisture and is only able to dry toward the exterior on the above-grade portion. There are two issues that get created:

A. Efflorescence and spalling begins to occur on the above grade exterior portoin of the foundation a 100+ year problem from a structural degradation point of view, but it can be mitigated with a sacrafisial parge on the exterior.

...but more seriously...

B: It raises the moisture content of the foundation sill and possibly the band joist to a level where it rots out (sometimes a sub-decade strucutral degradation issue.)

The solution is to put only semi-permeable or semi-impermeable foam against the foundation, but make it thick enough that the temperature of the interior side of the foam where it meets the wood studs is always above the dew point of the room air, even in winter. The "perm rating" of the foam is ideally between 0.5 and 1 perms, which is acheivable with 1.5-2" of XPS (pink or blue) which delivers ~R7.5-R10, or 3-4" of unfaced EPS(bead board- usually white), delivering ~R12-R16. That way ground moisture doesn't wick up the foundation- it can dry toward the interior of the basement. Under NO conditions should you put a vapor barrier on the inteior of the studwall, not even kraft-facers on batts (which are about 0.4 perms).

A combination of R10 of foam and unfaced R11 or R13 batts in the studwall that it delivers~ R19-R20 whole-wall values (thermal briging of the studs & plates included), and has a stackup that will reliably keep condensation from building up in the wood in our climate zone. That's what all the hygric analysis stuff is about in the this document:

http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis (http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis)

The best/most-cost effective solution is essentially case 8, figure 41, p.57 in that document. Read the moisture control paragraph, and print out the relevant sections for your inspector(!). The simulations were for a Minneapolis climate, which has a significantly cooler winter, with much higher condensation potential than in MA.

Note, they also simulated a foil-faced iso solution (case 9), which protected the studwall well, but note carefully the locations of the capillary breaks in the diagrams- unless your house has a metal or 10mil polyethylene sill gasket, you're stuck with problem B that I outlined above. If anything, errring toward a MORE permeable foam than the lower limit, say 2.5-3" of unfaced EPS (~R10-R12) would have been the ideal retrofit. If you're not changing out the 2" iso, make sure that the exterior of the foundation never sees snow buildup and that the whole foundation is well drained. If it's as well-drained below the footing as you think it is, you're probably going to be just fine. No house is built perfectly, yet they're still standing, but foil or poly vapor barriers against the foundation without a high-performance break at the sill isn't good building practice, in general.

FWIW: That inspector needs an education on this subject- insisting on a vapor barrier on foundation insulation is just plain WRONG (even though it's enshrined in the Canadian national building codes.) A vapor RETARDER, yes (XPS or EPS qualifies, as does closed cell spray foam at 1.5-2" thickness), but his insistence has no basis, and WILL create problems in somebody's house, hopefully not yours.

Whether it's 2" of iso or something else, as long as it's ~ R8 or more, it's well-worth the additional expense of unfaced R11 or R13 in the studwall, cutting the heat loss literally in half. Don't forget to put a capillary break (maybe your inchor so of foam you're putting over the slab) under the bottom plate of the stud too. (Even 1/4" of XPS is a sufficient capillary break, but if you put in right on the slab, put some poly underneath.)

In summer there's zero chance of condensation forming on the interior facer of the iso- butt the studs directly up against it- better yet, seal each bay with a bead of caulk before adding batts to maximize the performance of the fiberglass (which is very susceptible to convection and infiltration losses wherever there is a gap to convect into.) To get condensation the surface has to be below the dew point of the interior room air. If you dehumidify/air condition the basement to 60% relative humidity or less (recommended by ASHRAE- health professionals say 50%), even if it's 75F in the basement, that would put the dew-point at 60F. With ~50F sub-soil at the bottom of the foundation wall, with half the R-value in the foam layer, the place where it's 60F is inside the foam, protected from contact with the air. If the basement is 70F/60% RH, the dew point of the room air is 55F, but the facer is at 60F, still no condensation- you'll always win the summertime condensation game in summer anyway.

It's the winter, where at the above grade section will experience condensation for a random assortment of hours (the pre-dawn hours of the coldest winter days, typically), but never long enough to cause a problem as long as you have a sufficient ratio of foam-R to fiber-R. Even at 40/60 foam to fiber you'd be more than good in this climate, and center-cavity with R13 batts and R10 foam you'd be at 43/57. With R7.5 foam/R11 batts you're still at 40/60, and if you count the concrete as R1 (valid), R7.5 becomes R8.5, and you're at 39.5/60.5, which still has real margin if you use XPS or EPS, since the R value of those rise more than 10% when it's 0F on the cold side. (The rated R is the 75F number.) Iso drops in R value with temp, but iso rated R13@75F is still good for R11.5@0F. (The typical derated K-value for sub-zero use on iso is R5.6-R5.8/inch, down from R6-6.5 @ 75F.)

Before putting up the studs it's also better to air-seal the rigid foam by either taping the seams with FSK tape (2" foil tape often used to seal ducts) if foil-faced, or housewrap tape if XPS/EPS, or paint on some fiber-reinforced duct-mastic spread to ~1" either side of the seam.

If your iso extends all the way to the slab it's worth cutting back the bottom inch or so to ensure that there's no way moisture that might condense on or wick up through the slab wicks into the inteior of the iso, since there's no exit path for the moisture once it's between two foil facers. It wicks slowly, but it'll be semi-permanent if it ever gets in there.

danboston
03-31-2011, 03:09 PM
I used a combination of dry-lock paint and superthoroseal on the walls before I glued the polyiso boards to the walls and there is at least a 2-3" section of the floor extending outward from the walls that got inadvertently sealed. By shear luck, with application of the 2" polyiso boards onto the walls, the bottom portion should be in contact with the sealed portion of the floor.

Is it typically allowed to install electrical boxes in the wall with the foamboard behind it? That is another reason why I was considering a 1-inch air gap between the R-13 polyiso foamboard and the wood frame studs because that would give about 3.5" total between the foamboard and the 1/2' gypsum board on the interior wall. If not, then I might as well butt the wood frame right up against the polyiso boards. If the 2" polyiso foamboards give me R-13, you are saying I could/should add additional unfaced batting in the cavities to increase the R-value?

Finally, If I install pink/blue XPES foamboard on the floor, with 1/2" plywood on top, what is the best way to add tile on top of that for the basement bathroom? Should I use 1/4" plywood and then 1/4" cement board for that portion of the bathroom that will be tiled?

jadnashua
03-31-2011, 06:28 PM
The minimium I'd want to consider tiling to is 1/2" ply over foam, with C or better faces (i.e., no D faces) (on a subfloor, it's normally 5/8"). You might get by with 3/8", but that will warp some when you screw it down. Then, you'd need some cbu. If you wanted to do the insulation and get ready to tile in all one step, consider Wediboard. Expensive, but easy. It is the only tileable foam board (that I know of) that is approved for direct thinset bonding to a slab. Comes in various thicknesses, so you can choose the level of insulation (and cost$$) you wish to make.

danboston
04-01-2011, 07:24 AM
Wedi board looks pretty neat. Where can you get that stuff around here?

As far as mass for the heating system, the monoflo baseboard system is fed by 1.5-inch copper pipe. I calcuated about 13 gallons of water in the pipes at any one time (assuming 145 ft x 0.0918 gallon per foot).

Dana
04-01-2011, 09:05 AM
I used a combination of dry-lock paint and superthoroseal on the walls before I glued the polyiso boards to the walls and there is at least a 2-3" section of the floor extending outward from the walls that got inadvertently sealed. By shear luck, with application of the 2" polyiso boards onto the walls, the bottom portion should be in contact with the sealed portion of the floor.

Is it typically allowed to install electrical boxes in the wall with the foamboard behind it? That is another reason why I was considering a 1-inch air gap between the R-13 polyiso foamboard and the wood frame studs because that would give about 3.5" total between the foamboard and the 1/2' gypsum board on the interior wall. If not, then I might as well butt the wood frame right up against the polyiso boards. If the 2" polyiso foamboards give me R-13, you are saying I could/should add additional unfaced batting in the cavities to increase the R-value?

Finally, If I install pink/blue XPES foamboard on the floor, with 1/2" plywood on top, what is the best way to add tile on top of that for the basement bathroom? Should I use 1/4" plywood and then 1/4" cement board for that portion of the bathroom that will be tiled?

I believe it's OK to install the electrical boxes even if in FULL CONTACT with the foam (or at least I've seen it done that way MANY times, including with spray foam) as long as you have gypsum between the foam and the room interior. If anything leaving a gap would increase, not decrease the rate of flame spread in the event of an actual fire, since the studs would then not act as a horizontal firestop. Butt the studs up to the foam board no matter what.

And yes, adding batting in the stud cavites is a cheap & effective way to roughly double the whole-wall R value. It's safe from a mold/rot/condensation aspect in your climate as long as the foam is at least ~ R10 @ 20F (roughly your January binned-hourly temperature average) as foam, which you do. R13 iso isn't really performing to R13 at 20F, but it's still more than R11 even at 0F. The difference between R13 and R20 is something you can actually FEEL in the depths of winter, and adding the batts is easily economic in this climate in a 15 year NPV analysis on fuel savings alone were you to stick with an 86% AFUE oil burner using reasonable discount rate & fuel price inflation numbers (it's more like 20-25 years with similar assumptions and condensing gas burner.) It also allows you to down-size the radiation in that room since it's cutting the heat load nearly in half (assuming you have an R10 floor and few basement windows), offsetting the cost slighly. A general rule of thumb of long term cost-effectiveness for new construction in this climate is R10/R20/R40/R60 for slab/foundation/above-grade-wall/roof, but the true economics will vary widely by heating system type and fuel price inflation. Obviously retrofitting the above grade walls is daunting and not likely to be something you'd pursue (but it's not impossible-see: https://www.powerofaction.com/media/pdf/DER_Pilot_Pictorial.pdf), and not likely to be cost-effective, but retrofitting the as-yet unfinished basement is, in your case.

The fact that your existing system is somewhat higher mass is a good thing(!), but keepin in mind it's the mass of the smallest zone that's key to keeping the efficiency up and not short-cycling the boiler into an early grave or higher-maintenance. A decent system designer will run the numbers, but it doesn't hurt to do the rough calc yourself.

danboston
04-01-2011, 10:33 AM
Dana:

Thanks for the information on the insulation - very helpful.

The smallest zone is about 40 ft and that would give a mass of water within that zone at about 3.7 gallons. With that small zone therefore, I should think about adding more mass - i.e., a buffer?

Being a simple geologist, I'm still having a hard time wrapping my head around the "buffer" concept. Let me see if I have it straight: In your diagram showing the buffer with the "high flow resistance boiler", both the hot water output AND the cold return water enter the same buffer tank? If I get this straight, the buffer will provide a more steady source of hot water to the baseboard fins than if it was coming straight out of the boiler (which would be flashy at best) - is that accurate? It will also not only provide a more steady source, but because it is a larger source (mass) of hot water, it will be able to provide that to the fins for a longer duration? Hence, a more steady and comfortable temperature in the rooms that are accepting the heat AND the less time that the boiler is short-cycling to keep up with potential flashy temperature fluctuations in rooms accepting the heat in the absence of a buffer?

On the return side, the buffer will help to reduce the temperature of the return water before it goes back to the boiler and therefore increasing the efficiency of the boiler since the return water temperature has cooled even further and is at an optimum value? Furthermore, depending on how well the fins shed their heat, the buffer helps to prevent wide fluctuations in return water temperature back to the boiler? Thus minimizing the potential for "return water too warm" error messages showing up and subsequent atomatic boiler shut down in the new mod-con models?

If that is accurate, how does that work if you are sending both hot water directly from the boiler and cooler return water from the baseboard fins into one tank (the buffer)? Is there that much of a temperature separation in the buffer tank from top to bottom? Several contractors have told me that the water to be sent to the baseboard fins needs to be at around 180F. Does'nt the return water temp need to be at or below about 110 F for a gas-fired mod-con to operate efficiently in condensing mode? That would be a temperature difference of about 70 F in the buffer! (?). I thought I read in some of your other posts that the ideal temperature that can/should be sent to Al-fins is around 120-125 F? How do you balance that to keep temps from getting too low (for input to the fins) or high (for return to the boiler) in the buffer tank? What is the ideal temperature range of the hot water that should be going to the baseboard fins to provide adequate heat in the room, yet not too hot so that the return water ends up being too warm? Finally, what size buffer tank would be about right for my situation?

Dana
04-01-2011, 01:30 PM
I may have over-stated the cost-effectiveness-R values somewhat. Another opinion has R7.5/R15/R30/R65 for slab/foundation/wall/roof- see the minimums for zone-5, Table 2 on page 10:

http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones

But still, the rigid iso was the expensive part, and you're already committed to adding the studwall- the ecoomics of adding batts still make sense.

Wtih the buffer tank piped as the point of hydraulic separation between primary/secondary loops the boiler flow rate is independent of the heating zones' flow rate(s). The boiler throttles back more and more as the return water temp rises, and at some point the tank temp is high enough the boiler's controls kill the flame, even as the flow to the radiation continues, even tually lower the average temp of the tank. When the boiler re-fires, much of the output water from the boiler short-circuits across to the heating zone loops, reducing the high rate of mixing that would otherwise occur in the buffer. But that's just one common method of doing it. Yours is a simple/small enough system that it might be fine to simply put the tank in series between the boiler output and the zone-manifold. The pumping & piping details can and WILL differ.

A real design involves doing the math on the flow requirements & pumping rates for the zones, the pumping rates required by the selected boiler and the relative head- pressures, etc. Unless you want to take the course in hydronic design or home-study it, you really need to find the right system designer/contractor. This is not and will never be a design-by-web-forum type of problem except in the simplest of cases (and even then, you often only get what you pay for.)

Any contractor who still thinks ANY fin-tube requires 180F water is stuck in the 1950s, or didn't take the course, and surely never read a fin-tube spec sheet (http://www.slantfin.com/documents/675.pdf).

Many old school systems were DESIGNED to require 180F water to be able to be able to deliver the load AT DESIGN CONDITIONS (with a lot of padding built into the calculations- most could still work even then with 150-160F water on design-day), but 99% of the time it isn't -2F or 0F outside, and the heat load is a lot less. At ~35F the heat load is half the design load, and even in a minimalist system that required 180F water at 0F outdoors could keep the place cozy with 140F water.

Then consider:

A: The thing was probably overdesigned even for the leaky barely insulated 1950 version of the building with single-pane windows

B: You have fuel-use evidence that your true design-day heat load is closer to 30-35K and may be even less, a load easily met with 135F water in 145' of fin tube

C: You've cut the heat loss by probably 30-50% with your already-done insulation and air-sealing upgrades, and you're adding more insulation to the foundation.

Assume it was 50% overdesigned on day 1 in 1950 with 180F water (it was probably even more than that- 100, 200, even 300% oversizing isn't uncommon), and the design output for the 1950 house was in fact...

90K which is about the right output figure for 145' of fin-tube @ 180F (and suspiciously close to the 'heat loss" submitted by one of the contractors.)

...which means the real heat loss back in 1950 was really only....

60K

If you've cut down that 60K d heat loss 30% with insulation & better windows (it's probably more) it means you'd be currently looking at...

42K

... as your actual design condition heat load.

That's less than half the 180F output that it was originally designed for, and a BTU-rate the 145' of fin tube can deliver with sub-140F water. And that's on the COLDEST hours of the COLDEST days. Most of the time it can run even cooler boiler output. This is a VERY common scenario.

If it was even more oversized in the beginning (likely), or your improvements to date are better than 30% (also likely), you'd never need more than 125F-130F water to meet the heat load even during the coldest hours of the year.

Fin tube "sheds heat" primarily by convection, and it's output is very roughly (not perfectly) linear with the difference in temperature at the floor (~65F) and the water temp. At 180F that's an air-water delta-T of 115F. With 135F water that delta is reduced to ~70F, which is ~60% of the 115F delta, whtile the output is more like ~50% of the 180F numbers. (see the above linked short-spec for a particular fin-tube.) Because the fin-tube is relying on induced "stack effect" air flow for convection, that force gets to be really weak given the short height of baseboard, which is why it's tough to get reliable results with sub 120F output water in most fin-tube.

But even 130-135F water out will return 110F or cooler water if you set up the flows correctly, delivering low-mid 90s efficiency with a mod-con. From the description would appear you have sufficient baseboard on your existing zones to be able to run it there MOST of the time, maybe even ALL of the time, and a contractor with design skills can make that happen. (But surely not the guy who believes "Thou shalt deliver 180F water to baseboard" was engraved in stone by the hand of god.)

danboston
04-02-2011, 06:06 AM
Dana:

I appreciate the explanation of the boiler temperature going to and returning from the Al-fins - that makes sense and I can easily convey that to a contractor going forward.

So it sounds lke the buffer tank is used in tandem with the boiler and that hot water from the boiler may or may not go directly to the buffer tank, depending upon the temperature of water in the buffer tank and the room temperature? Sounds a little complicated and maybe that explains why not one contractor has mentioned it so far....

I have decided between three different gas-fired mod-con boilers: Burnham Alpine 80, HTP Elite 80 and the Prestige Solo 60. These units all have the same lowest min (16 K btu/hr). My heat loss rate is between 25 to 35 K btu/hr. Am I better off going with the lowest max available (e.g., the Solo 60) or does it not really matter?

Alpine 80 output (min/max) = 16/80

HTP Elite 80 output (min/max) = 16/80

Solo 60 output (min/max) = 16/60


Also, if properly sized, do I really need a buffer tank? If I need a buffer tank, what is your opinion about the Boiler Buddy?

I appreciate your information it has been very, very helpful.

Dana
04-04-2011, 01:06 PM
A Boiler Buddy is nice but, overkill for a system this small.

The need for buffering has noththing to do with the right-sizing of the boiler output to the design-day heat load, but rather the mass and output of the smallest zone relative to the lowest-modulated output of the boiler at the operating temp of the system.

Assume for instance your basement zone will have 40' of 3/4" fin tube and a 15-20 feet of distribution plumbing, which would have a water mass of about 10 lbs. Wtih 120F boiler output and 100F return water, you'd be putting 6Kinto the room, but would have 15K of boiler output at mid-mod, a 9K overrun. Assuming the boiler has an internal hysteresis of 10F in it's controls, it would take only 10lbs x 10F/9000= 0.011 hours(less than a minute) per burn cycle. Adding a 10 gallon tank in series would add 83lbs fo ra total of 93lbs, and you'd be looking at 93x10/9000=0.1 hours= 6 minutes of burn time- still not enough. At 30 gallons you're looking at ~260lf of water in the zone, and that would make for 260x10/9000=0.29= 17 minutes burn time at min-mod. But it's only half that if the hysteresis is only 5F.

Some small buffered Solo-60 installations I've seen were made to work with the zone returns all flowing through an unpowered HW tank that then feeds the boiler return. But whether that configuration works depends on if the head & pumping on each zone is low enough to guarantee the minimum flow on the boiler speced by the manufacturer. If it MUST be plumbed primary/secondary to meet the boiler flow spec, configuring the tank as the hydraulic seperator using Tees (as in the diagram from the other day) also works and is cheaper than a very-low-head Boiler Buddy or ErgoMax dedicated buffer.

Alpines & Solos have good reputations, but I've red no feedback on the Elite. As long as 0.86 x (maximum boiler output) or the DOE heating output number has at least some margin (even 10% is fine) over your actual heating design load they'll work, and with the min-mod numbers being the same they'll run at about the same efficiency. The experience & comfort level of the designer/contractor plus the local distribution support of the manufacturer generally trumps any of other differences between them. (Some installers rave about how easy it is to set up the Solo, but that's of little consequence once it's installed and tweaked-in.)

danboston
04-05-2011, 04:47 AM
Dana:

OK, it's clear to me that for low-mass systems (similiar to the one I have) that a buffer will help with decreasing maintenance and increasing the life of the boiler by creating less frequent and longer burn cycles. That makes sense. What about on the return side? Does a buffer also help with lowering the temperature of the return water even further - ensuring that it is 110 F or less and optimum for making sure that the boiler remains in condensing mode? Or, if we can use 125 F - 130 F output water for input into the fins, it is very likely that the return water would be in the sub-110 F degree range anyway and a buffer is not generally needed for for lowering the return water temp?

Just to reiterate so you do not have to plow through my earlier threads, we currently have 145 feet of Al-fin baseboard heating on two zones for the ground floor (1,700 ft2) that is conveyed using 1.5-inch copper pipe. My current smallest zone is about 40 ft and that would give a volume of water within that zone at about 3.7 gallons (assuming 40 ft x 0.0918 gallon per foot). This would represent a mass of ~ 31 pounds (assuming 3.7 gal x 8.35 lb per gallon). Within the next two months, we are planning to remodel the rooms on the ground floor and will be taking down interior walls and opening up the floor plan. It is a 1950's ranch and each room is boxed off from the other. Rooms will be combined and will allow us to reconfigure the zones on the ground floor so that they are roughly equal (Zone 1 = 73 feet and Zone 2 = 72 feet). That would represent ~ 55 lbs within each zone.

Secondly, when we do install baseboard heating in the 1,500 ft2 well-insulated basement, maybe I should think about using cast iron radiators instead of fin tube? What if I went that route with 40- to 50- feet of cast iron radiators in the basement as Zone 3 off the boiler? Would I still need a buffer under that scenario?

Not sure what size piping is typically used for installing cast-iron radiators, but I could always use a large diameter pipe to add additional mass if the cast-iron radiators are insufficient?

Thoughts?

Dana
04-06-2011, 09:20 AM
The buffer (in any plumbing configuration- either in-series or at the point of hydraulic seperation in a primary/secondary) doesn't appreciably affect the average return temp or the overall duty cycle, but HUGELY affects the number of cycles and efficiency losses related to the fixed losses of ignition & flue purges, and the wear & tear on the boiler.

Cast iron or flat panel radiators add mass (and work linearly at lower temperatures than fin-tube), but you still have to do the math on the total mass & heat-emission at the temperature you're operating to know whether you'd need a buffer. But since you probabably still need a buffer on the other two zones to run at 120F withtout short-cycling, making it a commoned buffer in series with the return manifold and the boiler is probably the right thing to do ( and not a seperate buffer just for the basement zone.) Plumbed on the return manifold is slightly better than on the output side, since then it doesn't slow the response time of the system when under low- partial load- the radiation gets to it's peak temp sooner without having to raise the temp of the buffer first.

A quick refresher on the simplified math: At your low-load minimum of 120F your existing 40' zone with the 31lbs of water the fin tube would be delivering something on the order of 200BTU/foot x 40' =1600 BTU/hr into the rooms, but the boiler is putting out nearly 10x that at 15000 BTU/hr even at it's min-modulation, for a ~13,400 BTU/hr shortfall. Assuming a 10F hysteresis in the boiler you'd get 31lb x 10F/13,400= 0.023 hour= 1.4 minute (83 seconds) of burns- a seriously short cycle. If you raise the temp to 130F the output of the fin tube would rise to something like 250BTU/foot stretching it out a bit, but not enough to matter.

To deliver the full 15K in a 40' zone you need 375 BTU/ft, which would take 150F water, with a return temp over the condensing point. You'd need to buffer your existing zones to be able to operate in the condensing region without short-cycling the boiler into both lower efficiency & an early grave.

To stretch the burns to ~10minutes (.17 hours) with 13.4K of extra takes a system with 10F of hysteresis at the boiler takes 13400 x 0.17/10F= 228lbs of water, which is 228/8.34= 27 gallons. You already have 3.7 gallons in the zone, so a 20-25 gallon buffer will do. But if the hysteresis is closer half that (sometimes is) a 40gallon buffer would be better. (30-50 gallon electric HW tanks are CHEAP compared to a 30 gallon Boiler Buddy or a Ergomax BT26 or BT48 buffer, and won't add much pump head to a low-flow system like this.) It would take ridiculously large diameter & expensive distribution plumbing to achieve that much thermal mass.

danboston
04-06-2011, 11:50 AM
Dana:

So, when I put heating in the basement, I should absolutely go with cast iron over fin-tube?

After weighing all my options, I have definitely decided to go with the Burnham Alpine 80. Burnham has a good reputation and the Alpine 80 modulating range looks good (16 to 80 K btu/hr) for my Heat Load (~35 K btu/hr). Also, I have found a couple of local contractors who seem competent and have installed quite a few Burnham boilers.

To get a better handle on the likely hysteresis of the Alpine, I looked up the Central Heating Setpoint discussion in the Alpine Installation & Operation (I&O) Manual (http://www.usboiler.burnham.com/products/residential-boilers-indirect-water-heaters/alpine)

According to the I&O Manual (page 94):

8. Boiler Temperature Regulation
a. Overview
Based on the call for heat type, the Sage2.1 controller
selects a firing rate target temperature setpoint.
Sensed temperature is compared to this Setpoint
to both adjust firing rate output and along with the
corresponding “Diff Above” and “Diff Below”
settings cycle the boiler.
b. Central Heat Setpoint
The Central Heat Setpoint is fixed at the contractor
selected value unless Outdoor Air Reset is enabled
or a “Setback” thermostat is connected. The value
of this setpoint is set up based on the type and
quantity of radiation installed.

Also on page 106 of the Alpine I&O manual:

The range of temperature values that the installer can input for the Central Heating Setpoint "DIFF ABOVE" is 2 F to 10 F (factory setting is 2 F).
The range of temperature values that the installer can input for the Central Heating Setpoint "DIFF BELOW" is 2 F to 30 F (factory setting is 10 F).

Does this help in the evaluation of buffer size?

It is interesting to note on Page 108 of the Alpine I&O Manual that the recommended Central Heating Setpoint temperature for Convection Baseboard Fin Tube Convective Heating elements is 160 F - 190 F.

Finally, which of the three diagrams that you provided in earlier threads of this post best represents what you describe as "a commoned buffer in series plumbed on the return manifold"?

Thanks, I appreciate all of your help!

Dana
04-06-2011, 03:46 PM
All prior schematic were variations on buffer-as-hydraulic seperator, none were a simple series-return diagram a partial schematic would look like this:




|boiler return input|<============<[buffer tank]<====<|zone1 return|<|zone 2 return|<|zone 3 return|

indirect return Tees in here-^

The returns from the zones all come together and feed into the cold input of your buffer tank or elec. HW heater, and the output of the buffer then feeds the return input to the boiler. If running an indirect HW heater as a seperate zone it needs to Tee in between the buffer tank and the boiler's radiation return.

Cast iron or high mass radiators aren't essential, but generally provide more comfort than fin-tube, since you can feel the direct radiation on exposed skin, whereas fin-tube is primarily just heating the air. Since you'll need a buffer to deal with your existing zones to run at low-temp, using the same buffer for all zones means you don't have to use some monster-sized radiators in the basement just to raise the thermal mass of that zone.

The fact that the hysteresis on the Alpine is programmable up to 10F means that you can indeed use a 20-25 gallon buffer rather than a 40-50 gallon buffer without short cycling on your 40' baseboard zone, as per the last paragraph of my prior post. If you run at least 40' of baseboard in your basement it'll be pretty similar to the setup for the other zones as far as buffer sizing. If left at the hysteresis programmed to the 2F default you'd still run into sub-5 minute burns, which would be bad for the boiler maintenance & efficiency. At 5F or less you'd need 40gallons or more to really stretch it out with that type of radiation.

Whatever you put for radiation in the basement zone, make sure it's output @ 120F water temps is at least that of your other zones, but in the same ballpark. Read the specs carefully. (If you're up for it, radiant ceiling is pretty nice, but that's a whole 'nuther design issue.)

danboston
04-06-2011, 04:50 PM
Dana:

That helps a lot. However, if you have an example of a simple-series return schematic that would be really great since I am having a hard time picturing that.

Yes, we plan to add a 50-gallon indirect water heater (Burnham Alliance stone-lined). One of the Burnham contractors said that the water in New England is not good and that a stainless steel IWH would not last as long as a stone-lined one. Do you agree with that?

On a side note I was able to download the free Slant/Fin Hydronic Explorer Heat Loss program. It is the same program that a previous contractor used to calculate a heat loss of 90 K btu/hr for my house. In addition to using an outdoor design temp of -10 F for my area (about 20 miles north of Boston), there were also some omissions they made for insulation. I plugged in an outdoor design temp of 0 F and added the appropriate insulation factors and came up with about 56 K btu/hr. That is still more than 1.5- times greater than the rate that I calculated using the NORA Fuel Savings calculator (~30- 35 K btu/hr), but I guess as long as it is less than the net I-B-R for the Alpine 80 (which is 63 K btu/hr) it should make the contractor feel good about the sizing. Do you know what the ASHRAE Outdoor Design Bin Temp is for: Boston , MA and Concord, NH ? If not, do you know where I can find those?

Dana
04-07-2011, 07:40 AM
The ASHRAE 97.5% design temp for Lawrence MA next door is 0F, the 99% number will be something like -3F or -5F. If the boiler's output is even 15% oversized for the heat load at the 97.5% number it'll keep up at -10F. For a listing of some ASHRAE 97.5% numbers see:

http://www.crownboiler.com/educate/heatloss.asp

For some 99% numbers see:


http://www.chromalox.com/resource-center/design-guide-pages/dg-comfort-heat.aspx (http://www.chromalox.com/resource-center/design-guide-pages/dg-comfort-heat.aspx)

Note, Boston's numbers are +9 F and +6F, due to the moderating effect of being on the coast. Figure on Lawrence/Andover's 99% number will be about -3F or -4F, not -10F.

Whenever I've used the Slantfin tool it's come out 35-40% ahead of measured reality. Other Manual-J or IBR type tools tend to hit in the 15-25% overage. If you use fuel use and degree-day data carefully to calculate the K-factor and parameterize the boiler carefully the NORA tool tends to hit within 10%, but can sometimes hit 10% low. The NORA tool tends to use some 99.9% number for design or somethingfor the cities on their pull-down menus. If the Slantfin tool is telling you your 0F load is 56K, measured reality will be no more than 45K. If the NORA tool is telling you 32K, it could be as high as 36K, but it's probably 32K. Unlike heat loss calculators, the NORA tool is using the boiler to MEASURE the heat load.

I suspect the Slantfin tool assumes an unrealistically high infiltration rate compared to that of tighter homes built in New England generally have, and pads out the result a bit from there. Better tools allow you to play around with air-leakage factors a bit more.

I have no opinion of stainless vs. stone lined. A generalized characterization of New England water is pretty bogus though- town water differs widely depending on source and treatment, but most towns don't have water hardness issues the way they do in the midwest. Call your town water department or if online, look up the water quality reports and see the average grains of hardness. Worcester uses primarily surface water from reservoirs, and I ran a tankless HW heater (notoriously sensitive for liming) for 15 years without ever having to de-scale the sucker, and retired it fully functional when I replaced it with a reverse-indirect buffering the heating system (necessary due to micro-zoning.)

To clarify in my previous post, "Whatever you put for radiation in the basement zone, make sure it's output @ 120F water temps is at least that of your other zones, but in the same ballpark." , I really meant to say "...at least that of your other zones relative to the calculated heat load for that zone..." The heat load of the basement will be much lower than the upper floors due to less above-grade exposure and less glazed area.

A series connection means that it's one pipe in , one pipe out, no Tees. Think of the tank as a fat spot in the pipe between where the heating returns come together and the boiler. All heating returns dump into the tank, not the boiler, only the tank's output feeds the boiler.

But IIRC from a recent thread on the boiler forum on this site the Alpine's min-flow requirements are such that it REQUIRES a primary/secondary configuration, so using the buffer (rather than closely spaced tees) as the hydraulic seperator is the right way to go, if that's you're boiler. (The Solo 60 could probably be done in series though.) See TK03's comments about P/S requirements for the Alpines here:

http://www.terrylove.com/forums/showthread.php?39849-Modcon-with-IHW-Tweaking/page4

You may want to read that entire thread- it's essentially the same design and setup issues that you'll have to address.

The LAST thing you'd want to do is up-size it to the Alpine 105, since it's min-mod output is probably going to be over half of your design-day heat load. The 73K DOE heating output of the -80 is well over even the Slantfin calc. The IBR number shouldn't be used here, since that's essentially a ~15% allowance for pipe & boiler losses when the boiler & distribution piping are outside of conditioned space, such as an unconditioned attics or crawl spaces, etc. Even if the boiler is installed in your basement, it's a conditioned basement inside the insulation, not a ventilated/uninsulated crawlspace. You very likely have 80-100% more burner than you need on the high-end even using the -80, but the fuel efficiency is dependent on how low you can go on the minimum. If your true 0F heat load is 35K, the -80 would nearly continuously (mostly in condensing mode) whenever the the outdoor temps drop below 40-45F once you have the flows & reset curves tweaked in. If you upsized the boiler to a higher min-mod, you'll experience more cycling losses when it's 30F or above (unless you added even more buffer), which is MOST of the heating season.

danboston
04-07-2011, 08:08 AM
The hardness of Town water has been consistent for years at 2 grains per gallon or 34 milligrams per liter. Is this enough to cause scaling problems?

As provided in the Chromalox web-site, the 99.9% ODT values for the following cities are: Boston [6 F], Worcester [0 F], Concord, NH [-8 F].
I re-ran the Slant/Fin Hydronic Explorer Heat Loss using -4 F for Lawrence as the ODT (average of the 99.9% ODT for Worcester [0 F] and Concord, NH [-8 F]) and that gives me 63.5 btu/hr. As I mentioned, based on oil consumption, the NORA calculator gives me about 35 K btu/hr.

After reading TKO3's thread, do variable speed pumps help with reducing short cycling by increasing the delta T?

As far as the size of the buffer, I just double-checked the pipe diameter associated with the smallest (40-ft) zone and it actually is only 3/4-inch copper pipe (the other zone is conveyed with 1.5-inch pipe). Apparently this smaller zone was added as part of an addition that was put on before we bought the house and they used smaller pipe for that zone. Therefore, we have a little less than 1 gallon in that zone. So, is a 20-25 gallon buffer still appropriate? Also, looking at the room-by-room Heat Loss numbers that I calculated using Hydronic Explorer, I added up the Heat Loss for the smallest zone on the ground floor and it is roughly equal (slightly less) than the predicted heat loss for the entire basement (insulated).

So you think the Alpine 80 with a 25-30-gallon insulated buffer and 50-gallon IDW heater is appropriate? The low end of the Alpine 80 is 16K btu/hr and the high end (DOE value) is 73 K btu/hr? Do you think that is still too much boiler and maybe a smaller combi-unit might be the better way to go? Do combi units provide a lower output (< 16 K btu/hr) than the Alpine 80?

jadnashua
04-07-2011, 02:12 PM
Combi units (those with a built-in HW coil) aren't the best idea when considering efficiency - the output is limited, and you have to maintain the boiler hot 24/7. An indirect, especially on a mod-con, means on a warm summer day, it may only fire once to bring the WH up to temp after the morning rush.

On a boiler plumbed with p/s, except for a few situations (heating the indirect may be one), the heated output goes in one loop back to the input. On that loop, there are some T's where there is a takeoff for your heating zones. It inserts the cooler return water on another T. So that there is actually flow in the secondary loop, the placement of the T's in the primary loop is somewhat critical. There would be one circulator pump for the primary and other(s) for the secondary loop(s). On mine, it pulls off the primary loop for the indirect, but that is not always done that way.

danboston
04-07-2011, 02:50 PM
The water piping diagram for the Alpine is shown here (see attachment):

12767

Where would the buffer go?

I looked at the HTP VERSA, which has a modulating burner that appears to range from 100 K btu/hr to a low of ___? Not sure what the low end is although they say it has a 5 to1 turndown ratio on the main combustion unit and a 10 to 1 turn down ratio for space heating - does that mean it will go as low as 10 btu/hr? It does appear to have built-in coil. So this does not act like a Indirect hot water heater and the storage temp of the combi must be maintained hot 24/7? Is'nt that how an indirect water tank works - it must be kept hot all the time?

See http://www.htproducts.com/versa-hydro.html

I am also considering having a solar hot water panel installed in my backyard. Massachusetts is offering a significant ($3,500) rebate program in addition to some Federal tax credits. I assume that would save the boiler from generating any hot water at least 9 months of the year. Of course I would need a larger IDWH (80 gall) and it would need to have two coils (one bottom coil for the solar heated fluid and the top one for the boiler). The other issue with the panel is location - it would be about about 80 feet from the house and another 50 feet to the tank in a conditioned space. The vendor stated that the piping would be installed in a trench 1.5' below grade and would be well-insulated. Not sure what the heat loss would be over that distance but have a feeling it would be pretty bad in the winter-time?

jadnashua
04-07-2011, 04:36 PM
That's a hybrid, similar (I think) to an older designed Trianco HeatMaker (Which I owned, but eventually threw out). Not in a position to evaluate it at the moment.

Dana
04-11-2011, 08:04 AM
The hardness of Town water has been consistent for years at 2 grains per gallon or 34 milligrams per liter. Is this enough to cause scaling problems?

As provided in the Chromalox web-site, the 99.9% ODT values for the following cities are: Boston [6 F], Worcester [0 F], Concord, NH [-8 F].
I re-ran the Slant/Fin Hydronic Explorer Heat Loss using -4 F for Lawrence as the ODT (average of the 99.9% ODT for Worcester [0 F] and Concord, NH [-8 F]) and that gives me 63.5 btu/hr. As I mentioned, based on oil consumption, the NORA calculator gives me about 35 K btu/hr.

After reading TKO3's thread, do variable speed pumps help with reducing short cycling by increasing the delta T?

As far as the size of the buffer, I just double-checked the pipe diameter associated with the smallest (40-ft) zone and it actually is only 3/4-inch copper pipe (the other zone is conveyed with 1.5-inch pipe). Apparently this smaller zone was added as part of an addition that was put on before we bought the house and they used smaller pipe for that zone. Therefore, we have a little less than 1 gallon in that zone. So, is a 20-25 gallon buffer still appropriate? Also, looking at the room-by-room Heat Loss numbers that I calculated using Hydronic Explorer, I added up the Heat Loss for the smallest zone on the ground floor and it is roughly equal (slightly less) than the predicted heat loss for the entire basement (insulated).

So you think the Alpine 80 with a 25-30-gallon insulated buffer and 50-gallon IDW heater is appropriate? The low end of the Alpine 80 is 16K btu/hr and the high end (DOE value) is 73 K btu/hr? Do you think that is still too much boiler and maybe a smaller combi-unit might be the better way to go? Do combi units provide a lower output (< 16 K btu/hr) than the Alpine 80?

Maybe I was too wordy in my response on that thread but simply put:

No, variable speed pumps do not and cannot reduce short cycling. It doesn't change the minimum modulated output of the boiler, or the rate at which the baseboards emit the heat into the room.

The lower the water temp, the lower the heating rate of the baseboard. When the boiler's output is many times that of the heat emitted the water temp rises rapidly and the burner kicks off.

To eliminate short cycling at condensing temps you either need more baseboard, or add mass to the heating zone, or increase the hysteresis of the boiler temp to use the thermal mass of the water in that loop.

From a practical point of view with 50 ' of baseboard at 120F you're looking at 1000BTU/hour, or about 7% of the boiler's ~15K output. Putting in 750' of baseboard won't cut it.

Raising the hysteresis of the boiler for 10minute min-burns on a sub-5 gallon loop takes it well out of the condensing zone for most of the burn.

Adding thermal mass to buffer the heat is the only real solution.

An Alpine 80 + indirect + buffer tank could be an appropriate solution. In that scenario, place the buffer at the point of hydraulic seperation to the heating zones, but not the indirect (I think you can eliminate P3 if you plumb it tight & right):


http://www.radiantandhydronics.com/Plumbing/Home/Images/1107-portal-GF-Fix-lg-edit.jpg

The HTP Versa is also an appropriate solution, and will run as efficiently as the Alpine 80 if usng fin-tube as the heat emitters. With radiant floors and/or panel radiatorsit's possible for a good designer to squeak 3-4% more efficiency out of an Alpine 80, since you could then run the heating zones at temps much lower than domestic hot water for high combustion efficiency. The Versa is inherently self-buffered, and making the system design & implementation comparatively simpler- you'd have to work at it to really screw it up (but I'm sure there are installers up to the task. :-) ) Unlike Trianco or Bradford-White combis, the Versa is fully modulating & condensing, with a 5/1 turndown ratio to (same as the Alpine 80's high/low ratio)- they're not really in the same class. Even though the smaller-burner Versa only cranks down to ~25K of outuput compared to ~15K for the Alpine 80, the 55 gallons of water in the smallest Versa is more than 2x the minimum buffer we were talking for the Alpine-80 solution with 10F of hysteresis, for less than 2x the min-mod burner output. There's literally no way to short-cycle it, and it'll average better than 90% efficiency at your anticipated fuel-use derived heat load using your given lengths of baseboard, since you won't need to it up above typical DHW storage temps- it'll ALWAYS be firing in condensing mode.

The heat loss out of a trenched-in solar loop isn't as bad as you might think. Heat loss is all about the total surface area, delta-T and R values. The surface area of the pipe is around 1/3 of a square foot per running foot, so at 80 feet out, 80 feet back you're looking at about 50 square feet. Assuming an average water temp of 90F and an wintertime soil temp average of 40F at that depth, and R10 of insulation (2" of closed cell foam) that's 50F x 50sq-ft/R10=250BTU/hr. That's the order of magnitude, and likely overstated by 34x, since the temps are only significantly elevated during mid-day sunny hours, which are less than 1/4 of all winter-hours, so the average delta-T may in fact be far less than 60F. Any losses to the conditioned space portion comes directly off the heating load, and can be ignored. Insulating underground flat-panel solar plumbing to a reasonably high-R can be done by sheathing the pipe in an R4 high-temp pipe insulation then strapping it to a strip of 2" of XPS and spraying 1.5-2" of closed cell polyurethane foam over that. If using evacuated tubes you may run into higher temps than XPS or SPF are rated for- let the solar designer spec the insulation.

The heat loss in summer would actually be higher, since the soil temps wouldn't be more than 20F higher, but the average water temps would be substantially higher due to lower panel losses and a greater fraction of sunny hours.

danboston
04-11-2011, 09:27 AM
Dana:

Great. I really appreciate your help.

So, if I decide to add solar hot water, I should stick with the Alpine 80 and a 30-gallon buffer tank. Under the solar scenario, for the IDHW tank I would need an 80-gall IDHW heater with two coils.

If I decide NOT to go with solar hot water, then the 55-gal HTP Versa sounds like a better option than the Alpine 80 with a 30-gall buffer. It would essentially be one unit, versus three; easier installation; roughly equivalent efficiencies, etc.

For the Versa-Hydro, would not a 10:1 turn-down ration on the space heating module result in an output of 13.5 to 135 K btus/hr? The Main Combustion System has a turn-down ratio of 5:1.

However, if I did want to go with Solar Hot Water, I do see on the HTP web-site that they offer an 80-gallon Phoenix Solar Hot Water tank (with 2 coils) that apparently can be used in conjunction with the Versa-Hydro.

Dana
04-11-2011, 11:48 AM
If going solar price out a Versa Hydro Solar (http://www.htproducts.com/versa-hydro-solar.html) solution before commiting to an Alpine 80 + solar solution. The Versa Solar is a fully integrated single tank system, with very little difference between the 80 gallon Versa and an 80 gallon Versa Solar, beyond the extra coil for the solar loop and some extra controls. With 80 gallons of buffe it would guarantees even longer minimum burns in space-heating mode.

Even if you never install the solar end it's efficiency would be as-good. It's a matter of the up-front costs of an 80 gallon Versa Hydro Solar with an as-yet unimplemented solar loop relative to the proposed non-solar solutions up front. An 80 gallon solar tank by itself is a pricey piece of hardware, and adding that to an Alpine-80 + buffer solution would mak for a more expensive total package.

Not to mention, with either a solar or standard version of the Versa most of the system-integration is pre-engineered, whereas with the Alpine 80 you're at the mercy of the system desginers/installers, and the quality of the design & commissioning a full-custom system will vary. It's pretty hard to screw up with a pre-packaged pre-engineered system.

danboston
04-11-2011, 02:19 PM
Dana:

I called HTP and they gave me more information about the Versa-Hydro. They offer three different-sized Hot Water Storage units (50-, 80-, 119-gal), but they all have the same burner. The Main Combustion Unit modulates from 26 - 130 K btus/hr, whereas, the Space Heating component modulates from 13 - 130 K btus/hr. Apparently they use a variable speed pump to convey hot water from the hot water storage tank to the heating elements and that is how they achieve the wide modulating range for the space heating. But to compare apples to apples, the Alpine has a lower modulating range (16 - 73 btu/s/hr) than the Versa-Hydro (26 - 130 K btus/hr) for the main burner. The smallest Versa-Hydro Solar unit comes with a minimum 80-gal dual-coil tank. As you said, an 80-gallon tank will provide plenty of mass and it will never short cycle. It is all one unit - no need for a separate buffer tank or separate IDHW tank. We also have the option of connecting solar hot water now or at a later date.

It does not appear that the Versa-Hydro tank or heat exchanger is made of stainless steel. Apparently, the heat exchanger is a 90/10 cupronickel alloy. Not sure if a cupronickel alloy heat exchanger is reliable?? The lack of a stainless steel tank and cupronickel heat exchanger makes me hesitate....

The Warranty on the Versa-Hydro is as follows:

Residential Use Warranty (1 year – Parts, 12 years – Tank)
COVERAGE
A. HTP warrants that it will repair or replace, at its option, any defective Versa-Hydro™ Combined Hydronic Appliance or malfunctioning component thereof that is found to have failed due to manufacturer’s defect during the first year after installation.
B. 1. Residential Use - During the second through seventh year after the date of installation, HTP will repair or replace, at its option, any defective Versa-Hydro™ found to have failed due to leaking heat exchanger, tank, or brazed plate exchanger.
C. Residential Use ONLY - During the eighth through twelfth year after the date of installation, HTP will repair or replace, at its option, any defective Versa-Hydro™ found to have failed due to leaking heat exchanger, tank, or brazed plate exchanger, at a cost to the purchaser equal to the following percentages of the manufacturer’s list price in effect at the date of replacement.
Year of Claim:
8 & 9 (25% to be paid by purchaser)
10 & 11 (50% to be paid by purchaser)
12 (75% to be paid by purchaser)

Here is the Warranty information on the Burnham Alpine:

ONE YEAR LIMITED WARRANTY ON RESIDENTIAL GRADE BOILERS
AND PARTS / ACCESSORIES SUPPLIED BY U.S. BOILER COMPANY, INC.
U.S. Boiler Company, Inc. warrants to the original owner that its residential grade
water and steam boilers and parts/accessories comply at the time of manufacture with
recognized hydronic industry standards and requirements then in effect and will be
free of defects in material and workmanship under normal usage for a period of one
year from the date of original installation. If any part of a residential grade boiler or
any part or accessory provided by U.S. Boiler Company, Inc. is found to be defective
in material or workmanship during this one year period, U.S. Boiler Company, Inc.
will, at its option, repair or replace the defective part.
HEAT EXCHANGER WARRANTIES
U.S. Boiler Company, Inc. warrants to the original owner that the heat exchanger of its
residential grade boilers will remain free from defects in material and workmanship
under normal usage for time period specified in the chart below of the original owner at
the original place of installation. If a claim is made under this warranty during the “No
Charge” period from the date of original installation, U.S. Boiler Company, Inc. will, at its
option, repair or replace the heat exchanger. If a claim is made under this warranty after
the expiration of the “No Charge” period from the date of original installation, U.S. Boiler
Company, Inc. will, at its option and upon payment of the pro-rated service charge set
forth below, repair or replace the heat exchanger. The service charge applicable to a
heat exchanger warranty claim is based upon the number of years the heat exchanger
has been in service and will be determined as a percentage of the retail price of the heat
exchanger model involved at the time the warranty claim is made as follows:

Year 8 (30% to be paid by purchaser)
Year 9 (40% to be paid by purchaser)
Year 10 (50% to be paid by purchaser)
Year 11 (60% to be paid by purchaser)
Year 12 (70% to be paid by purchaser)

Both of these warranties look pretty similiar.

Although it apparently does not appear in the Warranty description above, I saw in the Alpine brochure that US Boiler offers a free 5-year warranty on all parts and labor for the first 5 years from the date of installation. What are the chances that something will go wrong in the first 5 years with the Alpine?

Thoughts?

Dana
04-12-2011, 02:52 PM
Boilers & HW heaters are all pretty reliable for the first 5 years- even the crummy ones, and these aren't crummy ones. Both HTP and Burnham make quality goods that hold up when installed correctly, but a bad install can kill any piece of equipment. HTP also sells some low-end mod-cons (MC series) that DIYers seemed to manage to screw up the installations on, but work pretty well when done right. People have done combis based on their Phoenix condensing hot water heaters for something like a decade(?) without running into reliability issues.

On the heat-exchanger front, as long as you don't have leaks in the heating system or gross materials incompatiblity with sub components, the water side of the heat exchangers will last pretty much forever. Aluminum heat exchangers on boilers-past have had issues on both the fire side & water side, but SFAIK there aren't any generic or widespread issues with cupronickel alloys.

For the sub-flooring, even pressure-treated ply is overkill in a basement that NEVER floods. The XPS is an excellent capillary break against wicking up ground moisture, and at 1.5" it's only semi-permeable to water vapor. The only time you'd need anything other than a standard ply or OSB subfloor over an XPS-on-slab situation, is for flooding events. Structurally it's fully supported by the XPS & slab- it doesn't even need to be as thick as in a joist-mount but IIRC you need at least 1/2" of wood between the room and the foam as an ignition barrier. As long you don't have wood in direct contact with the concrete (pay attention at the edges) and don't put down a vapor-barrier type of flooring such as asphalt tile or vinyl-linoleum it'll have the same moisture content of any other piece of wood in the room. (Hardwood, bamboo, or carpet are all fine.)

Dana
04-12-2011, 03:13 PM
Ultimately, the quality of the system depends more on the quality of the system-design and how well it's implemented. Going with something that both installer & manufacturer back up with local support is more important than any warranty clauses. What this thread has given you is the basic education by which you can disuss the pros/cons of different approaches with the contractor better than the average homeowner/buyer would, and also gives you a handle on their competence or lack thereof. At the very least you're more likely to end up paying too much for something 4-5x oversized guaranteed to short-cycle itself into an early grave, expiring 10 minutes after the warranty does. Most residential boiler installations in MA are oversized relative even for the heat-load calculation software numbers, which are as a rule oversized to begin with. Modulating burners can mask some oversizing issues, but getting it right-sized (or adequately buffered) for the loads is always a better way to go.

danboston
04-13-2011, 05:26 AM
Dana:

Great. Your knowledge of boiler systems and the ability to convey that information is unbelievable and you have been of immense help. I really do appreciate it!

I will price out the HTP Versa-Hydro Solar. Looks like a great system and hopefully dummy-proof installation.

P.S., What about the 2x4 plates that need to be installed near the base of the interior foundation wall for the new framed wall? Those really cannot be "floated"? I plan to use pressure-treated 2x4s for the foundation wall plates that would be nailed into the concrete using a concrete nail gun. I should put a moisture barrier down between the concrete and the PT-2x4 plate? Are there any other options or steps I missed?

For the partition walls in the basement, I was planning to use 2x3's and float them on top of the 1/2"-plywood (which overlies the 1.5" XPS foam boards). They would be glued and nailed to the plywood - however, am not sure that would be sturdy enough. Should I nail them to floor like the 2x4's (I would have to rip PT-2x4s down to 2x3s but that is easy enough).

Finally, I wanted to use OSB sheets to float over the insulation since they come with a tongue and groove system - that way, I would not have the edges potentially buckling up/down where they butt up against each other. Home Depot has some T&G OSB product made by Home Advantage. The Advantech OSB boards are nice but are about 40% more expensive than "Home Advantage" boards.

Dana
04-13-2011, 08:58 AM
The studwalls aren't load-bearing, so putting the bottom plate above the XPS tapconned into the slab or just nailed/screwed to the subfloor is just fine.

T & G OSB is fine. It just has to meet a minimum fire rating (typically a 15 minute barrier per ASTM E 119 test ) to be used as the ignition barrier for the foam, unless you're putting down a wood, ceramic, or other substantial flooring that would add to the fire-rating of the floor assembly. IIRC most 7/16" & 1/2" goods and all 5/8" or thicker OSB out there meets spec on their own. The Home Advantage t &g subfloor goods are nearly 3/4" thick (and probably overkill, since it doesn't have to span between joists, and is 100% supported by the XPS + slab), so the fire-rating would be a non-issue.

danboston
04-14-2011, 05:24 AM
The HTP Versa is also an appropriate solution, and will run as efficiently as the Alpine 80 if usng fin-tube as the heat emitters. With radiant floors and/or panel radiatorsit's possible for a good designer to squeak 3-4% more efficiency out of an Alpine 80, since you could then run the heating zones at temps much lower than domestic hot water for high combustion efficiency. The Versa is inherently self-buffered, and making the system design & implementation comparatively simpler- you'd have to work at it to really screw it up (but I'm sure there are installers up to the task. :-) ) Unlike Trianco or Bradford-White combis, the Versa is fully modulating & condensing, with a 5/1 turndown ratio to (same as the Alpine 80's high/low ratio)- they're not really in the same class. Even though the smaller-burner Versa only cranks down to ~25K of outuput compared to ~15K for the Alpine 80, the 55 gallons of water in the smallest Versa is more than 2x the minimum buffer we were talking for the Alpine-80 solution with 10F of hysteresis, for less than 2x the min-mod burner output. There's literally no way to short-cycle it, and it'll average better than 90% efficiency at your anticipated fuel-use derived heat load using your given lengths of baseboard, since you won't need to it up above typical DHW storage temps- it'll ALWAYS be firing in condensing mode.


Dana:

When you say the Versa-Hydro will ALWAYS be firing in condensing mode, does that ssume that the return water needs to be 110 F or lower? Or is it the Delta-T needs to be at a certain threshold value? I had a contractor tell me that it is the delta-T, not the actual return water temperature that determines whether the boiler will enter into and stay in condensing mode. Also, as an FYI, the highest output T that the Versa-Hydro Solar unit (PHE130-80S) can generate is 160 F.

jadnashua
04-14-2011, 09:10 AM
A burner condenses when it's exhaust gasses are cool enough. To get that, the return water must be cool enough to drop those temperatures down. This is a function of the design of the heat exchanger, the exhaust path, the burn rate, and the return water temp...the return water temp must be low enough. Once it gets too hot, it can't condense. Now, if your supply temp was 130, the return would be low enough, but it is still a function of the return water temp.

Dana
04-14-2011, 11:24 AM
Depending on the exact mix of combusion air & fuel the dew point of natural gas exhaust in a mod-con is between 120-125F. The heat exchangers are thin & refractory for the lowest possible delta-T from the fire side to the water side, but in practical terms it won't be condensing much at all with return water temps much above 120F. If the contractor believes otherwise, he's saying the laws of physics are violable, and his statements on all matters technical need to be treated with great skepticicm.

The 160F high-temp limit on the Versa isn't a problem- with 145' of fin tube that would deliver ~60KBTU/hr for a sub-40K load. At 140F you'd be looking at ~45KBTU/hr out of the same fin tube, and with flows low enough for a 20-25F delta-T you'd be in the 88-90% range. At 130F the 145' of fin tube would deliver ~30-35K, bringing the return water temps down to ~110F, at which point your efficiency would hit the 92-93% range. Getting better than 92-93% is unlikely with any fin-tube system (of any length) because the abilty to get heat into the room with boiler water under 120F/return under 100F gets very limited and hard to model or design for, but with panel radiator or radiant floor/ceiling it's possible by carefully tweaking outdoor-reset control schemes. The Versa uses an outdoor reset curve for the heating system (which has to be programmed- the setup instructions are on page 60. (http://www.htproducts.com/literature/lp-314.pdf)), but since you'd probably never want the heating system output to go under ~120F (the fin-tube emittance modeling issue- it's not linear like the curve is) and your design-day heat load would likely never need more than 135F even at -5F outdoors, yours will be a very flat curve. But it's tweakable- and you SHOULD tweak it to as low a temp that still allows all zones to keep up as the outdoor temps fall. (It'll probably do OK at the default settings, but you can probably get another 2-3% percent out of it with some adjustments that costs you nothing but your tweaking & observation time.)

danboston
04-21-2011, 08:24 AM
Dana:

With Federal Tax Credits, State and local utility rebates, the HTP Versa-Hydro Solar system is by far the best deal. It's like getting the solar hot water system for free! I have posted a new Thread under "Water Heaters - Solar and Geothermal" pertaining to inquiries about Solar Evacuated Tube Panels...

Dana
04-21-2011, 02:15 PM
Thanks for the feedback!

I've not seen a Versa Solar installation in person- post pics (or pm me) of the installation details as it comes together, if that's the route you end up taking!

Shelly Brawn
10-20-2011, 10:16 AM
Dan,

Did you have any luck installing the Versa Solar Hydro system? I want to install one in my home, but I haven't been able to find anyone to take me seriously. I'm not a licenced plumber, and my town won't let me do it myself. I live off Rt 3, north of Boston.

danboston
10-24-2011, 06:53 AM
Shelly:

Yes I did have the HTP Versa Hydro Solar system installed. The contractor was great and is local. I had a hard time finding someone who would do it. He is relatively young and new to the business and is not tainted with oversizing boilers like most of the old school guys are. Send me an email to dfolan@yahoo.com and I will give you his contact information.

Tx, Dan