Air to water heat pump setup
Hello. I am looking for advice on the best setup for my hvac system for an addition on my home in the Hamilton Ontario area. My permits included a gas (LPG) boiler as the main heat source but I'm considering a heat pump system instead and getting mixed advice from local contractors. The main issue is most are recommending to avoid air to water heating for my hydronics. But I'll get back to that after describing my system layout.
My existing house is 1000sqft plus the basement and heated by forced air propane furnace. The "addition" is 2400sqft plus a 2400sqft basement. My garage is attached 1400sqft and a 1200sqft loft overtop. Now my approved plans have hydronic in floor heating for the new basement, garage and loft, and forced air hydronic air handler for the new main floor. Plans call for a 150mbtu Lochinvar Knight boiler which will also heat an indirect hot water tank and a 50gal buffmax. Sourcing a contractor for the job has made me question the complexity of my setup especially when I try and get away from propane and switch to heat pumps as LP is quite expensive. There doesn't seem to be a lot on the market for air to water heat pumps. I know there are lots when you google them but finding local skilled installers and people to service them down the road is a different story. These are the recommendations from contractors:
- Use air to air heat pump for the main floor and smaller boiler for the hydronic heating.
- Stick with the original planned system and avoid heat pumps altogether
- Use Air to water heat pump for hydronics, gas for main floor furnace and DHW.
- Two heat pumps, one for water and one for air (pretty expensive option)
So which option do you think is best? What heat pumps do you recommend that are easily sourced (including parts and warranty) in Ontario? Is there a single heat pump that can do it all? I would need up to about 160f on the air handler and 95f for my hydronics. What kind of setup do you run when you need different hydronic temperatures?
Anyway any help and guidance would be appreciated. Sorry for the long write up.
Comments
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Have you done a heat loss calculation? Everything starts with that.
Will you have air conditioning?
In Ontario, I'd guess that your cooling load is a lot less than your heating load. If you size a heat pump to your cooling load, it will be undersized for heating. Then make up the difference with the underfloor heating. Set the thermostat for the underfloor slightly higher than for the heat pump, so in the winter the heat pump only comes on when the underfloor can't keep up.
I would recommend a ducted minisplit like the Mitsubishi M-Series or Fujitsu Airstage.
A tank water heater is going to be simpler and cheaper to install.
Now you can do a head-to-head comparison of propane vs all heat pump: propane boiler and propane tank water heater vs air to water heat pump and heat pump water heater.
In your climate, I would look carefully at the cold weather capacity of air to water heat pumps. This is their real Achilles heel, it drops much faster than cold weather air-to-air heat pumps.
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You may be able to find an air to water heat pump to handle the 95 F water for the hydronics. It's not going to be cheap. You will really struggle to find one for the high temperature air handler. And that certainly won't be cheap. You may find a big enough air to air heat pump for that heating zone, however.
You won't find one which can do both.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Whenever I read "forced air hydronic air handler" my immediate thought is just use a ducted mini-split instead. You're completely losing all of the benefits of air-to-water by just sending the water to an air handler. The minisplit (air to air) is going to cost half as much and just about anyone can install them.
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As has been asked, has a heat loss calc been done? 150mbtu seems like a lot of heat for 2400sq ft of new construction. I would design a structure that could be heated with a fart if it were me. Insulation and air sealing is cheap when you're building. Equipment is expensive to purchase, install, power/fuel, and maintain in comparison.
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Outside of the garage, why not just duct the whole thing? You get heating and cooling, which you might not think you need now, but things change.
Otherwise, an air to water heat pump + low end boiler would be a great pair too. You could set it up such that the heat pump runs all winter, and is just supplemented as needed by the boiler.0 -
There are two Canadian companies that sell air to water heat pumps. Arctic in Manitoba and Nordic in NB.
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Yes. My heating load is 98kbtu and 57kbtu cooling load. Yes I will have AC. The current plan was to remove the existing furnace and connect new ducts to the old and heat and cool off one new system. An option I have (which I am leaning towards) is to keep the existing HVAC and run the new build seperate and have it split in 2 zones side to side. This would reduce my heating load for new build to about 67kbtu. The boiler was oversized a bit to run the indirect.
Im also considering not using an indirect and installing a tankless.
A lot of your sentiments are similar to what I have been hearing locally, so thats reassuring. Im going to do away with the air2water and consider the much more affordable minisplit system for the main floor.
I had convinced myself that somehow the air handler idea was more efficient or at least a more comfortable heat.
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I could do this. I have spent many hours debating this exact thing. I think at this point I mostly just like the idea of in floor heating. If it werent too complicated to convert my existing dwelling I would have run it on the main floor as well. I could save even more money and just put a overheat heater in the garage and forget the infloor all together. But I think this is a luxury Id like to make work. I do have ducting in the basement for the AC in the summer if needed; they will be shut off in the winter. I will also have a ductless miniplit for cooling the loft.
If I ran ducting up to the loft the runs would be crazy long and I dont care how good someone claims to be at balancing, there is no way the temp would be right if controlled from main floor thermostat. So whatever I do, the loft will be on its own zone.
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The entire build will be spray foamed and a 1" R5 wrap around the exterior. It will be as tight as it can get short of ICF construction. Im pretty sure my heat loss guy over estimated my heat load as he put 'average' for insulation and air tightness. I think these guys just have a standard worksheet and plug a few basic numbers in for each build. Perhaps someone else would have done a better job but you live and learn. As mensioned in my other post, the boiler was oversized for the indirect. I know technically thats not required or even advisable but my heat loss guy put it on the design. It seems these designs are just to satisfy the permit application and you can change anything at any time provided you meet the heat loss calc. My city inspector is pretty cool about this.
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Thank you everyone for your input. It has at the least made me simplify things a little. One thing I didnt mention to avoid biasing your responces is I am a licensed gas tech. This is only to say that I can service all my own gas equipment and also I have local dealer connections to purchase equipment at wholsale. Since I dont do AC work, I would be at the mercy of local contractors for install, service and repair of heat pump systems. So Id like some input on heat pump (mini split) brands and your experience with reliability. Especially after about the 10 year mark. I very much want to make the most energy efficient home but there is a certain comfort in installing what I know and am used to. If I was lucky enough to have nat gas I dont think Id be considering heat pumps at all to be honest. But LP gets stupid expensive in the winter. What would you do in my shoes?
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These loads seem crazy high for 3400 sf of basically new construction.
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avoid a tankless. No sense compromising, you have the space.
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The heat load is for the 3400sf home plus the 3400sf basement and the 1200sqft loft. The garage is not included and its heat loss is about 17kbtu. Total sf on the design is 7765+1400 for the garage. total heating according to my engineer is actually 115kbtu when including the garage. I know thats rediculous but its what the city approved and what I will have to design my system to. Attached is the summary of the heat loss from my designer.
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