Efficiency of Heat Pump Water Heater at 45°F
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HPHW in 40-45F basement
(I live in MA)
I’m slowly getting rid of all my gas appliances, and in removing our boiler and switching to a HP, the basement is now quite cold (typically about 40-45F). Yes, it is leaky, but we’re having insulation and air sealing done by MassSave in the few weeks.
I’d like to get rid of our aging gas HW heater and replace with Rheem Heat Pump Hot Water Heater (HPWH). Would a HPHW even be efficient at 45F?
We have 2 young kids… dont have a huge HW demand now, but will likely want as much capacity as we can in about 10 years.
Other options are pretty cost prohibitive: SANCO2/Sanden exterior HP with tank, HE Condensing Combi boiler, etc. If at all possible, I’d love to get rid of all things venting out the chimney.
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Replies
Mfg min operating temperature is 45F, but 40-45F seems unusually cold for a basement. It will probably be fine after insulation/airsealing basement.
Watch out for the height of the unit!
Very helpful-thank you. I'll hold off on installing until we've done the air sealing and such... crossing my fingers that the gas HW heater doesn't bow out before then.
The min temperature in the specs is for heat pump operation. Once it gets too cold, the unit switches to resistance heat and continues to run. I most cases this will only happen for a small percentage of the year, so overall, it is still the cheapest source of hot water.
I used to have a basement as cold as yours (100 year old house with 2' stone rubble foundation). Replacing all the leaky old windows and sealing up the rim joist area (especially under exterior doors on the main floor) made a huge difference. Now the basement is within two to three degrees of the main floor even with the uninsulated slab and foundation.
I would get the HPWH and work on getting the place tightened up down the road. If you are looking for extra capacity down the road, drain water heat recovery works quite well and pretty simple install if the showers are all on one stack.
The one nice side benefit of the air sealing work is the main floor is now much more comfortable since the floor is warmer.
I've noticed that rheem has a new 120 volt heat pump water heater that plugs into a 15 amp outlet and isn't a hybrid, there is no normal heating element, just the heat pump, and it is rated for use down to 37F. I could see getting the 65 or 80 gallon version of that, setting the water temp to 140, and using a mixing valve to adjust down to 110 or 120. Rheem's hyrbid versions are rated down to 40F for heat pump use but can also act like regular electric resistance water heaters is demand is higher or temps are lower. I'd try getting the basement temp up a bit even if not placing a heat pump down there. https://www.homedepot.com/p/Rheem-ProTerra-65-Gal-Tall-0-Watt-Element-Residential-Electric-Water-Heater-w-Leak-Detection-Auto-Shutoff-10-Year-Warranty-XE65T10HMS00U0/317100806
Yes, that 120v unit is the one I'm looking at. Other than electrical panel capacity and cost to install the line (which will be minimal in the grand scheme), is there any reason to not go with a 240v unit, though?