Heat Pump. Brochure annual COP 2.4 (no idea what it is at 0F). Single stage pump, variable speed air handler. 7.5kW heat strips.
I finally did what I was terrified to do, and logged into my electric account to see what our usage was during that window.
Nothing. Or at least, that's what the system logged. It shows zero usage 12/22-12/25. So something must be broken on their end.
In any case, ours is an entry level unit. In my anecdotal observations, 20F seems to be the threshold where it will be able to maintain the house at ~63F and only turn on the heat strips to defrost the coils. The air it produces is solidly warm but not piping hot at those temperatures.
Below 20F, and especially when the windchills are so low, most of the time the system was running in Aux heat mode. It solidly met my expectations, although (and I chalk this up to the thermostat and where it's located) there were times when it cycles every 15-30 minutes.
We don't have any burnable hat sources in our house. It's 100% electric save for a fireplace that needs to have the top two clay tiles and the entire cap re-done. The fireplace was almost never used by the previous owners, some of the grout is still the original color! To supplement our heat pump, we have in-ceiling resistive heat* and baseboard heaters in a couple rooms. We try to rely on the heat pump as much as possible, but it's also a retrofit system and so the duct trunks run through the attic, with the vents and returns all right near the ceiling. The unit is also installed over the garage which is insulated but unconditioned. We do keep a oil radiator space heater in the living room to keep DW&kids comfortable at closer to 68F.
In other words, there's room for improvement.
When we were shopping for a new system earlier this year, it was hit or miss whether we would be able to get our hands on anything other than an entry level unit. We may not have been able to get anything other than the system we have at all, at least in our area. If we did, we were going to pay a big premium too - all in ours was $9750, but something like a 16SEER/9HSPF was going to be $12k, and anything higher was creeping up into the $14k+ range. It's also important to remember that what's entry level today would have been a mid-tier or higher system just 5 or 6 years ago.
The pump it replaced definitely was not working. With the old system, when the average daily temp was ~32F, we were using ~120kWh a day. Yes. That's correct. With this system, it's about 65-70kWh a day. The utility notes that we used 2,216 kWh in the same period over Dec. 2021 vs. 1,284 kWh this year.
The best part is that it's enough of an incentive to look into getting more insulation blown into the attic. What we have is Circa 1982 when the HVAC was first put in and the addition to the house was built, but it's nowhere near enough compared to today's standards. I'm hoping that we'll see at least a 25% improvement on the energy efficiency, along with the air sealing that needs to happen with that. I've been following the DIY insulation thread and I'm torn on whether to DIY or to hire someone.
I, too, have plans to have backup wood heat. I'm hoping I'll be able to repoint and recap the chimney this year. My neighbor has all the tools, I just need to find the time. I also am strongly considering putting a pellet stove in the basement and having that tied into the other side of the chimney (we have two flues, one of which doesn't even connect to the fireplace). That's a longer term project but one which would produce some very potent radiant heat for the super cold days.
Regardless,
This (heat pumps) is the future for climates which don't get downright frigid. Governments at varying levels are slowly disallowing installation of fuel based heat/hot water in new residences. It takes some getting used to, having the air from the register at ~90F vs piping hot. Some people aren't going to enjoy it, but our family has gotten used to it. The technology is only going to get better, and higher performing units are going to continue to fall in price. I wouldn't be surprised if 10 years from now, the entry level models are ones which can operate at a COP of >2 below 0F.
*Yes that's a thing