So my first experience of a frozen coil it was 0deg F out and wind-chill of -20deg F. The cold air from outside the house was back drafting through the exhaust/the coil. I added a backdraft attachment on the exhaust, the ice on the coil melted within a few hours and thought that would be the end of my freezing issues.

Yesterday it froze up again. However this time it was a high of 50 degrees outside but since my house is rather air tight the heat is rarely kicking on. I believe this lack of air movement in the basement helped the freezing of the coil BUT definitely was concerned that I made the wrong decision of getting a hybrid water heater. Anyways, I turned my furnace fan on along with 2-3min of a hair dryer on high heat to start to melt the coil.

I just called Rheem with my concern and they said that I have a faulty sensor and they are sending someone out to change it as part of the warranty.

I can hear my high school physics teacher scream just about now: “energy cannot be created!”

What I failed to mention in the above example, is the difference in efficiency. Both heat pump mode and the resistance mode will have to transfer 2.46 kWh of energy to water. Resistance mode will do it using about 2.6kWh of electric energy. Heat pump mode will need about 25-30% of that.

Peter, mine is the basement, and I try to avoid ever using resistance mode. In fact, in the last three years I think I switched it to hybrid one time when we had family over, including 2 teenagers.

Your basement heating system will need to make up a relatively small heat loss to the HPWH. In a cold climate, it might be equivalent to opening the back door for a couple of minutes. Is running the extra heat better than switching HPWH to resistance mode?

Let’s say your HPWH has a 4200Btu heat pump running for about 2 hours/24h. That’s about 2.46 kWh of energy transferred from basement air into water (giver or take) over 24h. To make up that heat energy in your air, your heating system will have to come up with 2.46kWh or 8400Btu in a 24hr period. In this example, that’s not a lot, but your mileage will vary.

To transfer the equivalent amount of energy to water by using resistance mode, your 4kW heat strip (assumption) would need to run for about 36 minutes. Let’s say the resistance mode is 95% efficient, so that’s about 2.6kWh electric energy you’d need to supply.

Thanks for all the responses. I am thinking maybe I’ll duct the exhaust to the return air with a damper and option to vent to the laundry room if it doesn’t work out in the winter months… And then if that doesn’t work I can always switch to resitance mode. I am interested to see what the latent load of air drying the laundry might do as well… This will be an interesting and exciting project thanks everyone.

Glad other minds are thinking about these things.
Wondered why there are not reasonably priced devices to control intake/exhaust from outside. As you say it would have to include humidity as well as temp, and dew point as Allison has taught, and measure both inside and outside values. Perhaps often the solution to indoor comfort is right outside. Seems so at my house.

Gene, with a LOT of HPWH usage, perhaps. Otherwise, its runs are far too sporadic to be a reliable dehumidifier, especially with all the extra laundry hanging around.

About basements: yes, in fact I left one wall in my utility room uninsulated. It’s completely underground, and the ground above is “covered” with the garage. For us in Atlanta, the ground 4ft below grade is always a heat source for the 45F air coming out of HPWH. It may not be the case in other places. Please see my comment above if you’re tempted to vent it to outside, though.

John, why don’t refrigerators have an outside condenser option for winter? I’ve been wondering about that for a while. Or, like you said, in Minnesota air, a little puff at a time through a 1-inch “straw”…

About exhausting air from a HPWH: you’d want to make sure that the energy (and moisture) balance works in your favor depending on outside conditions, because the make-up air is from outside. If it’s 50F and 95%RH outside, suddenly the 45F dry air from the HPWH isn’t so bad to keep. OK, that’s Atlanta winter. If it’s 20F and 25%RH outside… you get the point.