We have had air source heat pumps for house heating and cooling since 2014. For the most part, they’ve performed well, or, at least, there’s nothing inherent in the technology which has made the experience sound and enjoyable. If you hear hesitancy in that, you are correct.

We did this relatively early through an independent prime contractor, then called Next Step Living who sized and recommended the units, and subcontracted the installation, both physical and electric. Essentially, we were on the bleeding edge. That’s a bit of an exaggeration, but at least it was true in Massachusetts at the time.

It’s not quite clear what was the root cause of our problems. It’s possible that the design and the contractor ran a line at the extreme limit of capability of the Fujitsu ASU12RLF/AUU12RLF combination, or perhaps the installation or subsequent maintenance was done poorly. We actually have another ASU12RLF/AUU12RLF combination for elsewhere in the home, and its performance has been rock steady. The problematic ASU12RLF/AUU12RLF combination shut down in Winter several times, having lost all its refrigerant (which is really bad from a greenhouse gas perspective), and the contractor we had for maintenance basically kept refilling it, blaming the problems on essentially ghosts. They charged us a few thousand dollars in fees through the services. We eventually fired them and went instead with GassCo.

In the end even though Fujitsu worked with them to diagnose, essentially replacing the entire compressor with another ASU12RLF at no cost to us, in consultation we called it a loss, and decided to switch to Mitsubishi on GassCo’s recommendation. This was 3 years ago. It’s interesting that in the time between 2014 and then, and Fujitsu to Mitsubishi, we got a more powerful unit for less cost than the original ASU12RLF/AUU12RLF.

So, I’d recommend Mitsubishi to anyone considering this path. But that’s not what I wanted to talk about.

Air source heat pumps have limits. If it got to -22°C the Fujitsu heat pumps shut down, because they are working too hard. We’ve not had a cold spell like that, so I don’t know where the Mitsubishi’s limits are. We have an oil furnace backup in case of power outages that we’d rely upon in case this happened, with the idea that this is a really infrequent event. In fact, on average, we probably use more oil testing the furnace monthly to make sure it is sound than actually using it. (We get our hot water through an electric water heater that uses an air source heat pump in warm months.) But here’s the point.

It’s a safe bet that Winter temperatures will, on average be getting warmer. Accordingly, going into the future, air source heat pumps should be bigger wins economically than they are now.

So, consider that when you are looking at upgrading your heating system.

Also, the original reason we looked at heat pumps was because our electricity consumption for the previous central A/C we had was outrageously high, typically peaking in July. Jettisoning that and replacing with heat pumps was a huge win. Energy required and cost per unit time is roughly proportional to the difference between outside temperature and set point inside. It’s a lot easier to cool from 35°C to 21°C than it is to heat from -30°C to 21°C.