Boiler location in a basement closet?

[Nathan Davis]

I need a sanity check for my heating figures.

In the attached spreadsheet, you will notice the EDR and calculations on the Btu output and water volume for each of my hot water radiators. The Btu output and water volume look high to me. For instance, the “Entry” radiator has an EDR of 6.3 (it is 23” high and 5 tubes), and includes a total of 26 sections. I’m showing this will output 27846 Btu. Wow, that seems like a lot for a single radiator!

Moreover, if you look at the second page of the attachment, you will see that this same radiator should hold 25 gal of water. Again, that seems like a lot of water for one radiator. Are these calculations really right, or am I figuring something wrong?

If these calculations are right, then my existing system (see second page of attachment) holds 575 gallons. That seems incredible. It’s more than I can believe unless someone else can verify that I’m figuring things correctly.

I have four questions:

1. Since the capacity of my radiators seem over-sized for the Btu needed to heat the house, I notice that they never get fully hot before the house warms sufficiently to turn the thermostat off. Because there is so much water in the existing system, I need to set the thermostat to turn the boiler on at least 75 minutes before we get up in the morning. That is, there is so much water in the system that it still takes our 200K Btu boiler about 75 to 90 minutes to heat up all the water in the system. And even then, when I touch a radiator, it almost never seems too hot to touch. If my replacement boiler is 50% smaller than my existing boiler, then I wonder if it will take about twice as long to heat up all the water (2.5 hours)? Regardless, if I’m saving money due to a higher efficiency, that’s OK.

2. With the existing boiler, we usually turn the thermostat down about 3 degrees at night and while we are gone to work during the day. Since the replacement boiler will have a 10:1 turn-down ratio, I’m wondering if we will find it just as economical to keep the thermostat at full temperature, instead of turning it down 3 degrees?

3. The 100K Btu replacement boiler will still need to heat 550 gallons of water in the entire system. With such a large volume of water to heat, I wonder if I should consider adding a 50 gallon hot water storage tank for preheated water, constantly held at 180 degrees? Conceivably, I could even add a solar panel to keep that water preheated.

4. I’ve also noticed that the oxygen barrier coating for pex seems to rub off fairly easily. So I expect that some will get rubbed off as I install new lines. Is there any spray that I can use to reapply the barrier where rubbed off?

 

[Dana]

With a modulating boiler it's usually better to "set and forget" the thermostat, and fine-tune the outdoor reset temperature to the lowest temperature that still keeps up, but doesn't always satisfy the thermostat. That results in the most condensing efficiency, and there's no recovery ramp thermal lag from the high thermal mass of the radiation, since there's no recovery ramp needed. Operated that way the boiler is just putting heat into the water at the rate the radiators are removing the heat. It's not going to be heating 550 gallons of water from room temp up to 13oF or whatever the reset curve is calling for at the time- it's just maintaining temp.

With an indirect fired water heater given priority over the space heating calls for heat, a 50 gallon water heater with a 100K condensing burner will recover in about 1/3 the amount of time that a standalone 50 gallon heater would. At a net 90,000 BTU/hr (1500 BTU/minute) talking about 10-11 minutes to raise 400lbs of water (a 48 gallon tank) from a tepid 90F average water temp in the tank to over 125F. With the high thermal mass of the radiators the rads will still be delivering heat during that period, and when the tank is satisfied the boiler then resumes serving the heating zones that are calling for heat. During a single 2.5gpm shower the burn time for the tank recovery will be less than the time spent in the shower.

Bottom line: The house isn't going to lose even 1F in room temperature when giving the water heater priority unless you run 5-10 back-to-back 8 minute showers during the absolute coldest 2 hours of the year.

Using a PEX/aluminum/PEX oxygen barrier tubing eliminates damage to the aluminum barrier unless you really abuse the tubing. If using the exterior EVOH polymer oxygen barrier type of PEX you can probably just give a tight wrap of a temperature rated aluminum tape over any bigger scuffs if you're concerned. Transfer rates of gas diffusion is a vapor-pressure x area type of thing, and even a bunch of scuffs don't add up to more than a few square inches, miniscule compared to the total surface area of all the tubing in your house. If you flush the system every couple of years it probably adds more oxygen into the system that a few dings in the EVOH would deliver. I wouldn't sweat the small stuff. too much.

 

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[Nathan Davis]

By the way, Hello from sunny 76F Puerto Vallarta Mexico. I think that I've possibly found a better way to beat the cold than installing a new condensing boiler. But next week I'll have to face reality again.

And thanks for your input. You've answered some important questions, especially about the set-and-forget thermostat. It sounds like you are saying that I probably do NOT need to size the boiler to a larger size in consideration of raising the temperature of the water mass from 90F to 125F because the system will be simply maintaining the temp at all times. That's an important consideration since it means that I can get by with a smaller boiler.

In my location, the EVOH oxygen barrier PEX is cheaper than PEX-al-PEX, so I like your idea of simply applying aluminum tape to any scuffs on the PEX.

Air infiltration through my walls is almost nil because the walls are 1" real plaster over hollow clay tile. The plaster is fire-proof, water-proof, and almost infiltration-proof. I suspect that the air infiltration around the windows is about 100cfm for each of the 4 floors, for a total of about 400cfm. I don’t think there is much that I can do to reduce air infiltration around the windows other than to replace the window weights with tape balances and fill the weight cavities with foam insulation. Even if I do that work myself, it will still cost over $3000. And the $3000 fix might reduce the air infiltration by about 50%, which may not be worth the cost.

So, I feel almost ready to order a new boiler, valves, and start installing everything. But naturally, I'll wait another month until it's warm enough that I no longer need any heat.

This sounds fun.

 

[Nathan Davis]

I've noticed a Navien 110 boiler on sale with an 11:1 turn-down (10K to 110K), slightly higher than most other brands. How does their quality compare to Westinghouse or Lochinvar?

 

[Dana]

Navien's boilers have water-tube heat exchangers which have higher pumping head, and have to be plumbed primary/secondary in most heating systems (and DEFINITLY in yours.)

Kyung Dong Boiler/Navien is a first tier Korean boiler manufacturer, as is Kiturami (the manufacturer of the HTP & Westinghouse fire tube boilers.) Navien has spent the capital to develop their own north American distribution & support network, whereas Kiturami has opted to OEM the equipment to already established companies in this market. At home they compete head to head.

From a system design point of view the fire tube Kiturami units are a bit more forgiving, but this is still something that needs to be done by a pro to get right. Find somebody competent & capable of specifying every pump and valve in the system even if you are doing some or most of the installation. (I believe Morgan Audetat aka BadgerBoilerMN still does system design as a service.)

 

[Nathan Davis]

Today I finally returned home and looked up my "actual" NG heating costs for this year and last. I was surprised to discover that my actual NG heating cost for 2017 was only $720 after I discounted about $20/month that we spend for domestic hot water and cooking. So far this year (Jan and Feb) we have spent about 30% more due to a much colder winter and a slight rise in the cost of NG. If the coming Fall temperatures are also below normal, I project that my total NG heating cost for 2018 will probably be about $1000.

I am assuming that I can potentially save about 33% of my NG bill by using a smaller and a higher efficiency boiler, for a total savings of approximately $350/year. I also assume a total system replacement cost of $4500 to $5000. This would provide about a 13 to 14 year payback.

I also assume that the replacement system would provide a more comfortable temperature, and would enable me to raise the basement ceiling in a few places. However, I'm uncertain that a 13 year payback is cost-effective enough to balance the better comfort and basement ceiling height.

Am I missing something?

 

[Jadnashua]

NG pricing has been dropping, but that's not to say that it won't start going the other way.

Assuming you're comfortable with what you have, you could wait until it dies, then replace it. There may be some better opportunities available by then. There's also something to be said for a new unit with a warranty, that should be trouble-free.

I tend to replace things when they start to bug me, either from a reliability standpoint, or I just decide I want something new. In general, keeping things until they wear out saves overall. Spend some money to tighten up the house in other ways and your comfort level will rise, too. Budget to replace the system so it isn't as much of a financial shock. If it's not a shock at any time, your options are more flexible.

 

[Nathan Davis]

NG pricing has been dropping, but that's not to say that it won't start going the other way.

Assuming you're comfortable with what you have, you could wait until it dies, then replace it. There may be some better opportunities available by then. There's also something to be said for a new unit with a warranty, that should be trouble-free.

I tend to replace things when they start to bug me, either from a reliability standpoint, or I just decide I want something new. In general, keeping things until they wear out saves overall. Spend some money to tighten up the house in other ways and your comfort level will rise, too. Budget to replace the system so it isn't as much of a financial shock. If it's not a shock at any time, your options are more flexible.

One aspect that greatly "bugs" me is the 1928 vintage 3" iron pipe hanging about 12-14" below the basement ceiling. About 50' of the pipe is 3", the rest reduces to 2", and all of it hangs about 12" below the bottom of the joists. I'm bugged because it reduces the headroom in a basement that I want to finish, and frankly it looks ugly. The pipe exiting the 2008 vintage boiler is 2", so I wonder if I could replace all the 3" pipe with 2"? Of course, another problem is how to drill 2.5" holes in the middle of each joist, and then how to feed a 2" pipe through those holes? After all, every high-temperature pipe I know gets fairly rigid when the ID is 2".

 

[Dana]

Today I finally returned home and looked up my "actual" NG heating costs for this year and last. I was surprised to discover that my actual NG heating cost for 2017 was only $720 after I discounted about $20/month that we spend for domestic hot water and cooking. So far this year (Jan and Feb) we have spent about 30% more due to a much colder winter and a slight rise in the cost of NG. If the coming Fall temperatures are also below normal, I project that my total NG heating cost for 2018 will probably be about $1000.

I am assuming that I can potentially save about 33% of my NG bill by using a smaller and a higher efficiency boiler, for a total savings of approximately $350/year. I also assume a total system replacement cost of $4500 to $5000. This would provide about a 13 to 14 year payback.

I also assume that the replacement system would provide a more comfortable temperature, and would enable me to raise the basement ceiling in a few places. However, I'm uncertain that a 13 year payback is cost-effective enough to balance the better comfort and basement ceiling height.

Am I missing something?

Have you calculated the difference in cost in just moving the beastie-boiler and dealing with the makeup air & venting in the napkin financial analysis? This whole discussion started with whether and how to stuff the beast in a closet as part of the basement build out. This is really about the build-out of finishing up the basement space, not net present value of future energy cost savings.

A right-sized wall-hung low mass boiler doesn't take up as much physical space, and is more conducive to zoning for higher comfort and better floor-by-floor temperature control, and doesn't need make-up air, since it's direct-vented with the combustion air coming from outdoors. The size of the mechanical room can shrink.

 

[Nathan Davis]

Have you calculated the difference in cost in just moving the beastie-boiler and dealing with the makeup air & venting in the napkin financial analysis? This whole discussion started with whether and how to stuff the beast in a closet as part of the basement build out. This is really about the build-out of finishing up the basement space, not net present value of future energy cost savings.

A right-sized wall-hung low mass boiler doesn't take up as much physical space, and is more conducive to zoning for higher comfort and better floor-by-floor temperature control, and doesn't need make-up air, since it's direct-vented with the combustion air coming from outdoors. The size of the mechanical room can shrink.

Yes, in this case I could even eliminate the existing mechanical room because I can hang a condensing boiler almost anywhere, e.g. in the laundry room at the opposite corner of the house where there is more room for it. Unfortunately it's a tough choice because it's a $5000 option.

 

[Nathan Davis]

Yes, in this case I could even eliminate the existing mechanical room because I can hang a condensing boiler almost anywhere, e.g. in the laundry room at the opposite corner of the house where there is more room for it. Unfortunately it's a tough choice because it's a $5000 option.

I really don't know if my existing make-up air system is effective or not. When I installed the existing boiler in 2008, I also added a round 8" cold air duct that takes combustion air through a nearby basement window and routes it to the boiler air intake. At the boiler, the duct connects to a 20" x 20" x 8" plenum that sits about 3" away from the boiler intake. The 3" provides some space so the boiler can still use room air if the air duct somehow gets blocked. The air duct also contains a fan to force outside air to the boiler intake, and the fan and a duct shut-off valve are both triggered with a temperature switch located on the boiler exhaust. The fan speed is lowered significantly with a rheostat. Like I said above, I don't know if this really helps with the efficiency--I just found it fun to add when I installed the boiler, and it cost almost nothing to install since I already had most of the items at hand. I think the duct fan cost about $15 and the temperature switch was about $8. Everything else I already had. Oh yes, I forgot that I also slid some duct insulation around the duct, but I already had that, too. I have no clue if this reduces any air infiltration, or not--it's probably just another crazy idea of mine, but it was too easy not to try.

 

[Dana]

Force-feeding pressurized combustion air into an atmospheric drafted gas-burning appliance could lower the combustion efficiency if not properly proportioned. Hopefully this wasn't a big enough fan to pressurize the basement by very much. (Probably not, if you dialed back the speed of the fan.)

It's always a tough choice to retire a boiler that still has a decade or more of service life in it, even if it IS oversized. I scanned the thread for the model number- it's a Utica(?), but didn't find the model #. What is it?

Newer Utica gas boilers like the MGB series now come with heat purge controls as standard equipment, reducing the negative impact of oversizing by quite a bit. If you opt to keep this boiler, it's probably going to be worth adding a heat purging boiler control to minimize standby & distribution losses. With your high mass radiation there is probably sufficient thermal mass in the system to break it up into zones floor by floor with much risk short-cycling. With an outdoor reset mixing valve one can further reduce distribution losses, and use a "set & forget" approach to the thermostat and not have to deal with slow recovery ramps from setback. The combined cost of doing both modifications would probably come in on the order of a couple grand, including the zone controls, etc. The system would still have very short burn cycles when serving just the basement zone, but probably not a large number of those short cycles per hour, due to the low load and heat purge controller making maximum use of the thermal mass of the boiler itself.

 

[Nathan Davis]

That's a fascinating option with a lot of potential.
I remember that you mentioned it in an earlier post but I was too focused on replacing the entire system to follow up at that time. I just checked the boiler model and it is indeed a Utica MGB series, model MGB200HID. However, it has one of the older Aquastat relays (L8148E) for which the Aquastat 3200-plus is listed as a replacement. So it looks like this new heat purge control could offer a cost effective option that, although it doesn't offer the efficiency of a condensing boiler, would still offer an improvement to my existing system, especially if I also buy the outside sensor.

A side benefit is that it also offers the potential for installing a 3-zone system. And, installation of a 3-zone system means that I would need to install new plumbing from the boiler to the branches for each radiator. So, that enables me to get rid of that hideous 3" pipe hanging below the basement ceiling! When I checked the model number, I also looked more closely at the hot water pipe exiting the boiler, and noticed that it is a 1.25" pipe, not a 2" pipe like I earlier thought. So MAYBE I can feed each zone with 1.25" pex which I could possibly get to flex enough to install through the middle of the joists. I'm hoping that 1.25" pex for each loop along with 3/4" lines to each radiator would offer sufficient flow.

The biggest branch would go to the entry and one living room radiator (heating two 27,800 Btu radiators for a total of 55600 Btu). The other two living room radiators (one at 27,800 Btu and another at 8000 Btu) could be on the loop that includes the dining room (a total of 69000 Btu), and another loop could serve the radiators for the family room and kitchen (a total of 55000 Btu). The three loops could comprise zone 1 for the first floor.

I'm starting to get quite interested in this option. I am assuming that I would retain the existing boiler circulation motor and add 3 zone valves, one for each zone?

 

[Nathan Davis]

On a totally separate issue, I have noticed that my boiler system does NOT include a filter of any kind, and when refilling the system, I have NOT included any treatment. Since I'm going to either move the boiler and/or replace some of the lines, this would probably be a good time to address this. What do you recommend?

 

[Jadnashua]

Unless a boiler leaks, the water used to fill it fairly quickly becomes fairly neutral. A big problem with a leaky system is the continuous addition of fresh water that has some dissolved minerals and gasses...oxygen, in particular, is problematic as it causes rusting of the internal pipes and components. But, if there are no leaks, after a short while, all of that oxygen is bound to the iron as ferric oxide or rust and then things stabilize. Refilling any pipes can cause some of the surface scum to be released. A good, working air scoop in the system will help eliminate any trapped air and help prevent degradation of the system. Not sure if an actual filter would buy you much of anything, but I'm not positive either way.

 

[Nathan Davis]

I am getting fairly close to ordering parts to add an Aquastat 3200 and outside sensor to my Utica MGB boiler, and also to replace my SINGLE zone of 3" and 2" diameter hot water distribution pipes with a 3 zone system of 1-1/4 PEX pipe. This is a non-condensing boiler rated at 81% efficiency with a DOE rating of 165K Btu. The existing system heats the house fairly evenly and adequately. However, I'd like to finish my basement including getting rid of the 3" an 2" pipes that presently hang down about 12-14" below the ceiling. Before ordering all the new pex, fittings, and valves, I'd like to get inputs from others on considerations and potential mistakes that I may have missed for my replacement system.

As you can tell from the attachments, I've been having fun trying to figure out this new system.

Attachment 1 (Boiler Layout.pdf) includes a layout drawing of components that would be placed on a 3/4" plywood mounting board next to the boiler. I apologize for using the symbols normally used for a flow diagram instead of plumbing symbols, but my Excel spreadsheet only includes flow diagram symbols. Regardless, I have tried to label each symbol to clarify. The black dotted box at the bottom of the drawing includes components from my existing system, the red symbols represent the new hot water distribution side, and the blue symbols represent the new return side.

Attachment 2 (Zone Layout.pdf) includes a layout drawing of the potential replacement 3 zone circuits along with loads for each radiator and each branch line. The red lines indicate hot water distribution circuits and the blue lines indicate return lines.

I can think of at least 3 considerations:

1. You will notice that in this replacement design (see Zone Layout.pdf), the radiant heat lines under the first floor kitchen are fed from the basement zone. I am a little concerned about this. A month ago, however, I installed those new radiant lines on the existing single zone system and connected them about 12 feet upstream of the radiator labeled 27.8K Family Rm. Now, the radiator labeled 27.8K Family Rm barely gets warm and fails to adequately heat the family room. This has surprised me because my understanding is that the 120' of 1/2" pex under the kitchen floor should output only about 3K of heat. It seems that such a small Btu load would not affect the 27.8K radiator, but it has affected it greatly. So in the new design, I have put the under-floor kitchen radiant heat as part of the basement circuit. Naturally, this means that the kitchen floor heat would be controlled by the basement thermostat, not the best way to do this. Since the "zone 1 west branch" only pulls 61K of heat, it seems that adding the kitchen radiant heat to that branch should pose no problem. Unfortunately it has made somewhat of a problem for the existing single zone system. What do you think--should I put it on the "zone 1 west branch?"

2. I'm also feeling a little leery about replacing the existing 3" and 2" distribution lines with two lines of 1-1/4" pex, and reducing the flow into each radiator to a 3/4" line. Each 1-1/4" pex line has an ID of only .87", for a total of 1.74" for the two zones. And the fittings reduce the flow even more. Thus, the existing 3" and 2" lines provide more than double the flow. Most of the existing radiators are fed at the radiator with a 1" or 1-1/4" line, so I'm also concerned that the new 3/4" feed into each radiator may be too small. But from the zone layout diagram, you will note that the largest single radiator outputs only 33K Btu. From what I've been reading, a 3/4" line should easily output double that amount, and a 1-1/4" pex line should easily carry more than 150K Btu (the amount needed for the Zone 2 west branch). Am I seeing this correctly?

3. The existing boiler circulator does NOT include anything that indicates it's flow rate. However, it is a TACO 007-F5 circulator running at 3250 rpm. I would think that anything running at 3250 should output more than I need. Since it outputs enough for the existing system, it seems that it would be enough for the replacement, too. But the reduction to 1-1/4" pex has me somewhat worried. What do you think?

And most importantly, what have I missed?

 

[Nathan Davis]

And to the above considerations, I also add a 4th consideration:

4. I really dread trying to drill 1.5" holes and feed 1-1/4" pex through my basement ceiling joists-- I assume that it is fairly rigid. So I've thought of an alternative-- attach the pex to the bottom of the joists, and use 2 x 4's to frame out the ceiling around the pex. Since 2 x 4's are 1.5" thick, it will drop the ceiling by only 1.5", and even then, not the entire ceiling but just a 24" wide raceway for the pex. But I'm bothered by the possibility of a nail puncture in one of those long runs of pex. Maybe I'm just paranoid. After all, I can't imagine anyone trying to hang a picture from the ceiling. But in my house, Murphy is alive and well.

A bigger concern is that pex grows so much with heat, and I will have some "straight" 30' runs in those raceways.

 

[Dana]

The Taco 007 is a work horse of the industry, one of the most popular circulation pumps ever. The RPM aren't as important as the GPM at any given pumping head (the "friction" of the plumbing and boiler's heat exchanger.) The Taco 007e is a high efficiency version with a comparable pumping curve that will use about 1/4 the amount of power (sometimes less), which is important if installing an outdoor reset control, since it'll be running a much higher duty cycle. Either will deliver 8 gpm at a pumping head of 8-10 feet, but the 007e dials back the power when the pumping head is higher 10', say when using a valve to dial back the flow. Setting the flow as low as possible to achieve the needed heat transfer saves power.

Better yet are programmable pumps with similar pumping curves where you can set the GPM, or back pressure or delta-T etc.

Most systems with fat pipe and high volume radiators have much beefier pumps than the 007. The fact that the heating system still delivers the heat with that pump is a good sign, and likely indicates that reducing the pipe size probably won't be a real problem. But it's better to do the math on that.

If you're setting up home-runs to each radiator from a manifold you probably don't need PEX any fatter than half-inch between radiator & manifold, an you might be able to use 3/8" for most of them. But you have to do the math.

Like I've stated previously, spending a bit of money now on letting a competent hydronic design professional with the experience and design software spec every pump, valve, and new piping on the revised system will save you a lot of time money and frustration in the end. Hydronic design is not merely a plumbing exercise.

 

[Nathan Davis]

When I start to upgrade my boiler distribution system with new pex, I will need to connect to threaded connections at each of the existing registers. I've always used Rectorseal T+2 for threaded connections because it seals so well. However, I'm now wondering if the soft thread compound might tend to migrate back to the boiler and start to seal up some of the heat tubes? Should I use something different, like conventional plumber's putty?

 

[Dana]

You're worrying too much. There's plenty of turbulence created by flow at the heat exchangers to keep it from sticking inside the boiler.