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Heat Pumps Perform Well During Deep Freeze

By Angela Kantola

As a volunteer with the Metro Denver Green Homes Tour, I often interview prospective homeowners for the tour. After the nearly week-long "deep freeze" of sub-zero temperatures in metro Denver in mid-January, I asked five of our heat-pump homeowners from the 2023 tour how their heat pumps had performed. Four homeowners were completely satisfied with how their heat pumps had performed. One (new to Denver and in their first winter here) learned they needed to use their wood stove backup in an upper level great room for extremely cold weather. Here's what the homeowners said:

"Comfy!!! During the recent several days of zero or below temperatures our heat pump system kept our home warm and comfortable. We have a ducted unit and one mini-split head. An auxiliary resistance strip in the ducted unit kicked in more than usual (and "usual" is really very infrequent).

"My heat pump did fine. I tend to keep my house on the cool side (about 67), and I did notice for a bit the thermostat was reading ambient temp at 65. (I didn't turn on the ceiling cassette at all, so that was the whole-house unit only.) used a space heater in the living room one evening for a little extra warmth, but was otherwise fine. Once I upgrade insulation, I'm sure that will help. (Right now the heat pump is working with original 1960 insulation and doors.)"

"My heat pump performed well. Upon waking, the house temperature was 3-8 degrees below the set point of 68 in both zones (ducted cold climate heat pump that serves two zones). I was prepared for this as these temperatures are the rare 1% of coldest nights. I could either get a strip heater for my heat pump for these situations or use a supplemental heating source. This year I used my gas fireplace as a backup during the day and a space heater in one room on occasion."

"I still have my [19-year-old] dual system with the heat pump working until it dips below 30 degrees and then the gas furnace portion kicks in. However, I had extensive insulation and air sealing work performed this fall and it made a significant difference during this Arctic Blast."

"During the cold snap the heat pumps could not deliver 69 degrees in the big room we have. It got to 61 degrees at best and we needed to bundle up or get the wood stove going. It was not comfortable. If it is only one or two days a year it is survivable but if we were to start again we would certainly want the design to include a back up for these days. The heat pump cassettes in smaller-volume downstairs rooms performed well."

Heat pumps are more efficient than gas furnaces and are an important component in "electrifying everything" to reduce our dependence on fossil fuels.  Our informal survey confirmed that:

1)  "BIG INSULATION" is vital, so improve your home's envelope as best you can before installing a heat pump system.

2) In metro Denver, 3 degrees Fahrenheit is considered a reasonable “heating design temperature” (where ~1% of annual heating hours fall below that level). When outside temperatures go well below zero – especially over several days – a typical home heating system isn't expected to maintain a thermostat’s set point. Most everyone (heat pump users and those with older heating systems) needed a little auxiliary heat to get through our recent extreme cold event.  

If you're considering a heat pump, we hope these homeowners' experiences will help you determine how a heat pump can best work in your home.     


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