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Community and Q&A

How is your heat pump working?

Steve Vigoren | Posted in General Questions on

Just wondering how folks with heat pumps are making out. The last half of December – first half of January have been real winter here in MN. I am in CZ 7, Northern MN, we just had the coldest night of the year at -33F. I have a Hyper Heat MUZFH15NA outside unit and a MSZFH15NA indoor unit heating a one story 1344 square foot home. (18K btu/hr heating capacity) Thermostat set at 72F. At 2AM I got up to check on things and the heat pump was shut down. My baseboard electric comes on at 67F and was just coming on. At 7AM it was -33F and the house was 66F. By 8AM the sun came up and started its job of warming the Southern exposure house. By 9AM the baseboard thermostat turned it off. At 9:15 (-28F -Weather Channel) the heat pump started its defrost cycle and a few minutes later started putting out heat. The outdoor unit is in the sun in the morning so that may have warmed it up some. As can be expected, I am very happy so far with my set up. I got the heat pump fired up Dec. 20, and it has been heating the home on its own since, with the coldest previous low temp was -25F. By 11AM it was -13F and we are expecting a nice warmup into the +25F range within the next couple days :-). I did turn off the HRV before bed last night, and I had a little condensation on the windows at the bottom of the top pane in my double hung outie windows, even got some ice in the corners, I turned the HRV back on at -18F and the windows are drying up.

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  1. GBA Editor
    Martin Holladay | | #1

    Thanks for sharing your experience. Good to hear everything's working. In most cases, the coldest nights are usually followed by sunny days -- which is a good thing.

  2. Stephen Sheehy | | #2

    Here in semi-tropical Maine, it hasn't been colder than about -10°F since we moved in, but our Fujitsu RLS3H minisplits have been fine. I think any well insulated and well airsealed house can coast through the occasional really cold nights.
    Our power was out for about 18 hours recently, with temps in the 20s and 30s, but inside didn't go below 68°.
    Side note: Our usual insurance company refused to insure our new house because they were convinced that heat pumps can't work in our winters.

  3. Expert Member
    Dana Dorsett | | #3

    The Mitsubishi mini-splits are designed to turn themselves off at some temperature below -18F, but it's apparently not a precision number, just a maximum (warmest) temperature at which it might turn off.

    Fujitsus don't do that, and may be preferable in locations where temps cooler than -18F are a regular wintertime occurrence. But if it's only a few 10s of hours per year it would be hard to see in the power bill, since, the difference in efficiency between a mini-split at temps cooler than -20F and a baseboard heater isn't really huge, a COP of 1.1 - 1.5 vs. a COP of 1.0.

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