Water heaters for radiant heat and hydronic air handler

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dangina

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installing radiant heat in my new house bungalow I'm building, I also want a hydronic air handler for the upstairs (my sons have severe eczema) had a calc BTU load done for the house, said system needs to be 74000, was looking at buying :
http://www.thewholesalewarehouse.ne...ent-stainless-steel-natural-gas-water-heater/
Its a htp phoenix light duty just rebranded at a cheaper price, was thinking about buying two of them, one for the heating of the house, one for DHW, figure if the one for my heat goes, I can just move the one over and get a cheap dhw heater until i get the unit fixed. I live in canada close to the border so these aren't available here. Just wondering if this is possible to do, I'm dont like the tankless units I have seen nothing but problems from those who have them, I do like the condensing hot water heaters and what they offer...
 

Dana

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That's got to be one gia-normous new bungalow to have a heat load of 74,000 BTU/hr! What is your 99% outside design temperature? Or is that 74,000 BTU/hr with some local code required minimum oversizing factor? Who performed the load calculations, and how?

For comparison, I live in a 2400' antique 1920s vintage bunglow with an additional 1500' of conditioned basement that has a heat load only a bit more than half that @ -15C. (My local 99% outside design temp). My house would still be well under that 74K number at -30C (which doesn't happen in my neighborhood.) In new construction with current code insulation and windows it would be lower still.

The Phoenix Light Duty would surely do it, and with the high water volume would be self-buffering for cutting it up into micro-zones. But it's probably still more expensive than HTP's UFT-080w wall hung boiler that probably more appropriate for the task. (The same boiler is also sold under a Westinghouse nameplate as the WBRUNG-080W.) This is not a tankless hot water heater- it's an inexpensive but still pretty nice modulating condensing boiler with a stainless steel fire-tube heat exchanger, with sufficiently low pumping head that it can easily be pumped direct rather than configured as primary/secondary making it pretty easy to design a system around. It can also modulate down to about 7500 BTU/hr out, so it doesn't take a whole lot of zone radiation to balance against it's minimum-fire output, even at condensing temperatures, yet can still deliver 75,000 BTU/hr out if/when needed.

I'm not sure how an air handler zone is suppose to help with eczema (my kid deals with it too). While air handlers have filters, moving air stirs up dust mites and other allergens that contribute to eczema. If air filtration is what you're after, an air filter that runs 24/365 is a better solution than a heating/cooling air handler that only runs in duty cycles in proportional to the heating or cooling load. Low temp panel radiators are definitely more comfortable (and stir up less dust ) than air handlers & ducts. Air handlers also pressurize/depressurize rooms relative to the outdoors, which drives air infiltration rates higher than the natural infiltration rates, which in turn makes wintertime air much drier than with radiators or radiant floor, which can be an aggravating factor for eczema.

What do you have in mind for air conditioning (if anything)? If ducted heating is a definite, a 1.5 ton Fujitsu mini-ducted mini-split is also good for about 19-20,000 BTU/hr in heating mode @ -15C. They make them smaller if need be to cover just one zone. Unlike the typical air handler + boiler configurations, a ducted minisplit modulates, and if right-sized for the load would run nearly continuously, varying it's speed with the load. From an air filtration point of view that is superior to say, a 1-2 speed First air handler with a hydronic coil and a split-system cooling coil. The mini-ducted versions only have a rated output down to -20C, but wall coil types may be sized for an individual bedroom's loads, and some have a rated output down to -25C or a bit cooler.
 

dangina

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WOW! Thanks Dana for responding! I'm still new to all of this and learning as I go by reading other peoples q&A on the forums. A few answers to your questions: My house Is a 2040sqft bungalow with a full 2040 of basement all with 9 ft walls and half of the upstairs has 12' walls. I live in lethbridge, AB canada and I had one of the local hydronics experts do the load calculations for my house, So I was hoping they would know what they were doing based on the build materials and local weather calcs. We can hit as low as -35C here, but I couldn't tell you my 99% design temp, it is pretty mild majority of the year due to the high winds and chinooks we get here.

I wanted to go with the PHLD as I will be using one in my shop as well, and if worse came to worse I could also switch it out for one of the house ones if they fail. Its still way cheaper buying these out of the states than anything we get up here, so price wise its not too bad.

the wife is still against rads in the house(I've tried and tried but still can't convince her) the hydronic air handler seemed liked the best option as we can run ac off of it and a humidifier, and if for some reason we don't like the system down the road, we can always go back to a furnace seeing how all the ducting is already in place. Not sure if it would help with eczema, but I'm willing to try anything as the house I'm in now has none of these things.

when you say run a air filter 24/7 which units are you talking about? Do they hook up to your furnace/air hadlers?

I'll look into ac mini split system, I'm hoping we can get away with an ac unit under a 3 ton. If you had to go with an air handler which ones would you choose? Right now I'm currently looking at the nu-air enerboss en7p with the built in HRV.
 

Dana

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The listed 99% outside design temp for the airport in Lethridge is -16F/-27C. A code minimum indoor design temp is 20C, so you're looking at a interior to exterior temperature delta of 47C.

HVAC contractors rarely use Manual-J methods, and even when they do they use ultra-conservative assumptions about air leakage and the quality/level of the insulation or using unrealistic indoor & outdoor design temperatures, which usually ends up oversizing the calculated level by ~1.3- 1.5x . They then multiply that by some other factor "just in case", often oversizing the equipment by 2x sometimes more, which is bad for both comfort & efficiency. That way they reliably avoid the 5AM call on the coldest night of the year from the shivering irate customer, but they're not really doing you a favor by oversizing (especially if you have it broken up into zones.)

Professional engineers and energy nerds run more aggressive numbers and are more likely to hit it right.

Rules of thumb are really crude and fraught with error but a decently tight 2x6 wall construction with code-min windows typically comes in at about 15 BTU/hr per square foot at -20C (a 40C delta) for the above grade portion, with neglible additional load for an insulated below grade basement. At a 47C delta that would extend to about (47/40) x 15 = ~18 BTU/hr per square foot, call it 20 BTU/ft due due to the 12' ceilings in part of the house (taller windows too?) so for a 2030' house you're looking at a likely design load in the 40,000 BTU/hr range, at most 50,000 BTU/hr (unless it's a walk-out basement with a lot of exposure.

ASHRAE's recommended or oversizing factor as the optimal compromise for comfort/efficiency is 1.4x so upsizing from 40K would put you in the 55,000 BTU/hr range.

With a ~40K-50K heat load the UFT-080W has plenty of burner to spare for running an indirect hot water heater as a separate zone. This will probably be substantially cheaper than a separate Phoenix Light Duty, or a pair of them. (The Westinghouse version runs less than USD$1700 from multiple online vendors. A 40-50 gallon indirect hot water heater would be under $1500. ) Operating the indirect as "priority zone" suppressing heating zone calls when the tank is calling for heat guarantees excellent HW performance, and the tank temp recovers quickly (2x as fast as traditional standalone tanks), well before the house begins to cool off.

A heat recovery ventilator (HRV) with a recirculation mode can filter air 24/365 running continuously at very modest air volumes. In your climate it's better to build the house super-tight and run active ventilation, and lower the ventilation rate in winter if it gets too dry rather than running a humidifier. Humidifiers often increase the mold spore counts, and amplify the rot-risk/mold hazards of any leaks in your vapor barrier. If you run a humidifier, keep it under 35% relative humidity in winter. In an air tight house you can usually control the humidity by dialing back the ventilation rate if it gets too dry. This works pretty well for folks who don't create a lot indoor air pollution, but people who smoke, use lots of aerosol sprays, or cleansers with volatile human hazard components shouldn't back off the ventilation rates that much.

Something like a middle of the road Venmar HRV with recirculation mode is on the order of USD$1200-1500, and the installed cost in my area would be USD$2500-3000 if done in new construction. The ducts are tiny compared to what's usually used for AC or heat. (6" hard piped trunks, 4" branches.)

By divorcing the ventilation function from the heating or cooling function you have complete control over the ventilation rates, since the duty cycle isn't dependent upon having a heating or cooling load, and you can crank it up for periods when it might be needed (say, when roasting a goat in an open charcoal barbeque in the middle of the family room or something. :) ), and dialing it up or down to whatever feels comfortable the rest of the time.

If radiators are out, would microzoning using thin profile hydronic wall coils be acceptable to the boss? (That would work with either a hot water heater or a low-modulating boiler like the UFT-080W.) The advantage of local wall coils is that they don't drive outdoor air infiltration, or spread indoor air pollution to other parts of the house. And, by micro-zoning it's dead-easy to tweak the room-to- room temperature balance.

Unless you're building the lousiest least insulated house in AB or have a huge amount of west facing window, your cooling load will come in under 2 tons for a house that size. There are multi-zone mini-splits that might cover that (and most of your heating load too), but I'd be reluctant to use mini-splits as the primary heat source in a location that regularly sees -35C unless it's a high-performance house, well beyond code. But cooling is a different animal. Point source cooling with 1-3 wall coil type mini-splits (no ducts) usually works just fine in 2000' houses. A 2 or 2.5 ton multi-split will typically support up to three zones on one compressor, and you can put the coolth exactly where it's needed most. Multi-splits are as a rule heat pumps too, and during milder weather (down to -10C to -15C or so) something like a Mitsubishi MXZ-3C30NAHZ would have sufficient capacity to run at very high efficiency, giving you some options, even though it doesn't have enough low-temp capacity fully to cover your heating load at -27C. (A mini-duct cassette can serve 2-4 nearby doored off rooms, if need be.)

As with heating, a room-by-room cooling load calculation by a competent third party (not an HVAC contractor) would be in order before fully specifying the equipment.
 

dangina

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55000 IS A LOT LOWER THAN THE 74000 I was quoted lol the windows of my house are fairly large and majority of them are facing south, put we will be getting some higher grade windows to combat the sun. No walkout in the basement. We will be running the house super air tight with the spray foam insulation, thats great info to know about the HRV vs having humidification. I was thinking of humidification only because our area is very dry due to the winds never stop blowing. I didn't know that the new ventilation systems worked that well. Seems like you can pick up the Venmar HRV at lowes so getting filter replacements will be easy.

The only reason the wife was against rads to begin with is that it limits furniture placement in the rooms, I wonder you could have furniture in front of the ultra thin wall coils? Do the wall coils provide cooling as well or does one have to rely on mini splits instead?

I appreciate the time and care you took to answer my questions Dana, hopefully this answers some questions others may have had thinking the same thing I was thinking! thanks again!!!
 

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Hydronic wall coils can work for cooling only if you have a hydronic chiller, but that's a whole other engineering project that's still pretty rare in N.America (though catching on a bit in Europe.) A 2 ton Chilltrix would probably cover your cooling load (and a large fraction of your heating load at -10C) , but getting design & system support could be a bit difficult. A mini-split/multi-split approach would be more straightforward, since it's a pre-engineered "system in a can", with fewer ways to screw up.

As long as you have a few cm of space under it you can back the chesterfield right up against the thin profile wall coils. They have a quiet blower that pulls air in at the bottom (or bottom grille, depending on model) , and directs the air up at the top. But the control panel is on the top- you would't want to place a tall bureau directly in front.

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It's common to place them under a window, which is where you might have a bed or chair, but probably not anything tall anyway.

With a lot of window area your peak heating & cooling loads go up, but your net heating energy use goes down. You might run your own room by room Manual-J using aggressive assumptions with an at least half-decent online Manual-J/Manual-S tool, see what you come up with. You could also download and run NRCAN's Hot 2000 tool on your design as a second opinion. Nailing down the room-by-room loads is important for figuring out how much heat emitter (be it radiator, radiant floor or ducts) is needed.

If you want to do it manually using pencil & paper or a computer spreadsheet tool, a 2x6 wall with a 25% framing fraction (typical 16" o.c. stud spacing) with 5.5" of half-pound density open cell foam, half inch plywood sheathing and half inch wallboard and vinyl siding typically comes in with a U-factor of about 0.065 BTU/hr per square foot per degree-F difference. With 24" o.c. framing that drops to ~U0.061. Using 20C (68F) interior design temp and and the ACCA's listed -16F that's an 84F delta-T, so every square foot of wall area contributes a design heat load of 0.065 x 84F = ~5.5 BTU/hr to the heat load.

A typical argon filled double-pane window with one low-E surface comes in at about U0.34 BTU/hr per square foot per degree-F. If it's something else a better description of the glazing is in order. (Canadian window rating systems reflect net heat gain (solar gains against overall losses, which doesn't directly translate into a U-factor the way US windows are rated.)

A typical solid exterior door runs about U0.5, insulated doors ~U0.25.

For the approximate ceiling or basement U-factors I'd need to know how those are insulated.

With more detail on the wall stackups & framing I could give you a more accurate U-factors. Mind you, with even an inch of exterior rigid rock wool or rigid EPS foam over the entire exterior of the sheathing the U-factor drops by quite a bit, from U0.065 down to U0.050, which is usually pretty easy to incorporate. That is a much larger performance improvement than bumping from half-pound foam to 2lb closed cell foam in the wall cavities (and a lot cheaper too.) Across the border in the US an inch of continuous EPS sheathing on an 2x6/R20 would still be ~R0.5 shy of code minimum for that region, but it's still pretty good, and easy enough to build.

With insulating sheathing thicker than 1" it gets a bit more complicated, but high performance builders in New England regularly put as much as 4" or more of rigid foam on the exterior of framed construction, using 1x4 furring through-screwed to the studs to clamp the foam in place, hanging the siding on the furring. At 1" you can usually just long-nail/long-screw the siding in place (except in hurricane zones), and probably wouldn't constitute a large design change.
 

dangina

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With a ~40K-50K heat load the UFT-080W has plenty of burner to spare for running an indirect hot water heater as a separate zone. This will probably be substantially cheaper than a separate Phoenix Light Duty, or a pair of them. (The Westinghouse version runs less than USD$1700 from multiple online vendors. A 40-50 gallon indirect hot water heater would be under $1500. ) Operating the indirect as "priority zone" suppressing heating zone calls when the tank is calling for heat guarantees excellent HW performance, and the tank temp recovers quickly (2x as fast as traditional standalone tanks), well before the house begins to cool off.

wouldn't it be cheaper to run the phoenix instead of the UFT-80 and buying a separate water heater? Is it possible to do everything I want with the uft-80 and a phoneix combined for the air handler and radiant and DHW? how do you pipe that together to make it work?
 

Jadnashua

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Had you considered hydronic in-floor radiant heat? No issues about where you place the furniture, and warm feet is always nice. If you have pets, they'll love it too. This would also allow comfortable use of tile or wooden floors verses carpeting (although that can be used if you engineer it properly), which is both environmentally better, less likely to generate dust, and usually last much longer while looking good verses carpeting. Boiler temps generally need to be lower, which helps with efficiency, too. A hydronic coil in an air handler would need the boiler to be fairly hot to provide comfortable outlet air temps (moving air tends to cool, so must be hotter) to be comfortable).
 

Dana

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Radiant floors (except for slabs) it quite a bit more expensive than panel radiators or hydronic coils. It isn't necessarily 10x as expensive, but it's more than 3x.

The wall coils don't blow directly on the humans for minimal wind chill, unlike poorly implemented ducted systems. With the right air handler even ducted systems have comfortable output at the registers using 50C water out of a water heater or boiler. Wall coils can be comfortable at even lower water temps. A 50C output water temp yields return water temps well into the condensing zone for condensing natural gas equipment. In most cases we're talking lesss than a 2% difference in average combustion efficiency, but a bigger increase in total power use when heating with air handlers or wall coils than an all-hydronic/no-air system.

A UFT-80 + indirect HW is usually less expensive up front and higher efficiency than a hot water heater based system, but not always. If you're not up to running the numbers for doing the hydronic heating system design, hire someone to do it for you in order to save you the expense & frustration of a major do-over when it doesn't quite work. Hydronic heating design is far more than a plumbing project, with lots of ways to screw it up. There is at least one competent resource posting on this site that will do custom hydonic system design via internet as a service familiar with HTP's equipment and designing hot water heater based systems, etc.
 

Tom Sawyer

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As it is he's going to have close to thirty thousand wrapped up in this if he continues down this path. IMO, that's just wasting money on a system that will never pay itself back especially considering the average life cycle of boilers today.
 

Dana

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Yep- spending USD$30K for a heating system on a new construction house is silly. For USD$20K you can usually upgrade the thermal performance of a new house to the point where it can be heated & cooled with less than $10K of ductless heat pump (with a tiny wood stove for backup) , and a solar array big enough to take it to Net Zero Energy would easily fit on the roof.
 
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