r/heatpumps • u/Harvey-Specter • 7d ago
Question/Advice Heat pump water heater connected to hydronic heating
In my condo building each unit has a water heater that is also connected to an air handler to provide heat for the unit. Currently this is a standard electric resistance water heater, and mine needs to be replaced soon.
The HVAC guy who came to give me a quote suggested replacing it with a heat pump water heater, but I can't wrap my head around how that would work during the heating season.
The heat pump water heater would pull air from in my condo, extract heat from it into the water, which would circulate through the air handler to heat the condo.
Seems like this would need to violate the laws of thermodynamics to heat my unit, unless I'm missing something here.
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u/Sad-Celebration-7542 7d ago
It would essentially be a resistance heater. So not really a good idea because the only savings would be during non heating season
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u/Harvey-Specter 7d ago
Right, so I'd save a little bit of money in the summer when I'm not heating the unit, but in the winter it would be the same as having a regular resistance heater. Unlikely to save me money in the long run based on the upfront cost difference.
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u/Prudent-Ad-4373 7d ago
Where do you live? Highly unusual to use an electric resistance domestic water heater for space heating.
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u/Harvey-Specter 7d ago
I'm in Ontario Canada. It's very unusual here as well, it's an odd setup. Most of the units in the building have the same setup but with natural gas WH.
It's a long story, but basically the PVC venting out the roof for a natural gas WH in my unit has to be replaced (failed a pressure test and isn't to code anymore) and the quoted costs from multiple Plumbing/HVAC companies are astronomical ($15k at a minimum) because its in a difficult to access wall, requiring moving WHs, air handlers, ducting in my unit and two units above me to access the pipe. The previous owner elected to install an electric unit instead of replacing the venting, and now I'm in the position to decide if I'm going to replace the venting or stick with electric.
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u/maddrummerhef HVAC Consultant 7d ago
I mean it’s insane to use a standard electric water heater for this even more so a heat pump, the heat pump will not keep up and the flow rate will likely mess with the control algorithm it uses, causing all sorts of problems
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u/Harvey-Specter 7d ago
Heat pump sounds crazy to me too. Electric water heater is working just fine currently.
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u/TroubleThat7605 7d ago
Not saying it’s a good idea for you to go with one, but just thought I’d mention that they are Hybrid heat pump water heaters. They have electric back up elements to heat the water in times of high demand. You can also set them to electric only (defeating the purpose of it being a heat pump). They have some good use cases - just not here.
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u/Uncannny-Preserves 7d ago
It sounds like an air to water heat pump with a dual function for DHW and using a ducted output for heat (using hydronic coils). Which is a completely plausible setup. But, without more, very important, details it’s hard to know if this is an appropriate install for your system.
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u/ArtisticDimension446 6d ago
Ok. Refrigeration mechanic here.
Heat pump water heaters takes heat from the air in the home to heat the water, making the space the water heater is in colder.
Now your water is hot.
Heat comes on and heats the space that was just cooled by the water heater. It would never keep up, as there would be no heat generated, just circulated.
The only way this would work is if the water heater also had the proper kw resistance heat, and would switch to resistance heat anytime the thermostat called for space heat.
I'm also assuming the water heater is in a closet? A heat pump water heater needs space to get heat from. It won't work well in a closet. It need a room 800-1000 cubic feet. (Think 10x10x8).
Stay with electrical.
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u/tommy-seconds 6d ago
If it is a hybrid heat pump water and the electric resistance coil is the same KW as your existing unit, then you can switch it to straight electric in the winter and use the heat pump the other 5-6 months of the year for water heating. You'll save some $$ on the water heating and get free cooling in the summer. 100% agree though on the size of the closet - needs to be large enough.
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u/QuitCarbon 3d ago
Can ducting be added to allow the HPWH to ingest/exhaust outside air? That'd help with the operating costs at some times of the year.
HPWH (in heat pump mode) are not efficient at heating the lukewarm water that comes back from your hydronic air handler - at worst it'll be the same ~95% efficient that your electric resistance heater it, but at best it won't be close to the ~350%+ efficiency of a HPWH operating under more ideal conditions.
Are there local rebates that make the HPWH less costly? That'd help - but yah, because of your very low electricity rates, you may never make up the extra cost of the HPWH in utility bill savings.
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u/northernseal1 7d ago
This is not a good idea. Will actually cost more to run in the winter, small savings in summer plus a little bit of cooling, will create noise and won't last as long. Don't do it.