Wisdom of venting hybrid heat pump to interior space?
Looking at replacing a two decade old gas water heater with a new hybrid heat pump, to be installed in an insulated but not draft-proofed garage. (In the Seattle area, assume 40F-90F temp range in the garage, a bit less extreme than the outside temps.)
The garage backs onto the pantry, which during the summer is quite a bit warmer than we would like, since we do not have AC.
Is there any blocker on venting the chilled output air from the heat pump hot water heater through the wall directly into the pantry? It would keep that small space quite a bit cooler when it needs it most. The garage is clean, finished, and the hot water heater would be placed very near the garage door, where the ventilation is greatest.
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I see no reason why that wouldn't work, since the exhaust air doesn't have combustion byproducts, just cool, dry air. On a couple of projects I was able to have the back of the refrigerator open to the space with the HPWH, a similar idea that makes both appliances more efficient.
Be careful here. You must have an airtight fire separation between the garage and the house interior. If your HPWH draws its air from the garage and pumps it inside, this is a serious violation of that separation. Serious, because running a car in the garage WILL send carbon monoxide into the house. That can kill people. It's also a fire hazard because smoke and heat from a garage fire will also be pumped into the house, at least until something in the HPWH fails.
If the HPWH is located in a room that is made part of the "house" rather than the "garage," this can work, even if it is located in a closet accessed from the garage, but with air-sealed doors. You would also have to either pull the inlet air from inside the house or from outside, through fire-protected ductwork.
Thanks for the fire code thought, that's the kind of thing I was looking for. Since the garage is *ahem* currently being used for storage of not-car, car exhaust wasn't on my radar. I had considered general dust, possibly paint fumes during winter projects, etc, and had mentally added 'increased fume removal and cleaning'.
Good points, thanks.
(Although I'm curious about the air-sealed requirement, because I can guarantee you that the door from garage to pantry was *not* airtight when I moved in. Had to add the seals myself. Will definitely be looking up the codes for this unincorporated county location.)
Most states in the US have adopted the International Residential Code (IRC) in one form or another, though enforcement mechanisms vary dramatically, especially in unincorporated areas. Google your state's "residential building code" and start from there. You will achieve a state of enlightened boredom faster than you could imagine.
There are some codes regarding how far any building air intakes have to be from things that exhaust anything. Since the garage is a different kind of classification from the home in this regard, any airflow between the two is likely to be a problem. The one way around that might be if you put a fire damper on the vent duct, but I think you're best option is to NOT set anything up to bring air from the garage into the home. I would not prioritize energy efficiency over potential fire safety issues.
Bill