I remember a rash of nuisance service calls rolling in on weekends like this, the snowfall being the key part. It is amazing how well prepared a Heat Pump is for cold weather; with safeties, defrost controls, and supplemental heat (in most). Unfortunately, they do not come with windshield wipers to keep the condensers clear of snow, and snow will decrease the airflow across the condenser to a breaking point.

For conventionally ducted heat pumps, a situation like this means either the supplemental heat turns on more frequent, or the homeowner must turn on the Emergency Heat to satisfy the thermostat. When covered with snow, a conventional heat pump will not be able to move air across the coil and will actually start to recycle the air increasing the defrost cycle times and frequency. I see this often on 'top discharge' condensing units that may have been off during the snowfall, allowing the top to be covered. If not serviced, this can start creating quite the ice sculpture.

For the ductless, mini-split heat pumps, this could create an uncomfortable home. This is because these systems do not incorporate any sort of supplemental heat into their equipment. During defrost cycles, becoming more frequent during times of snow and airflow restriction, the indoor coil fan actually shuts down to avoid blowing cold air into the home. More defrost cycles tend to impede the operation enough that it could not meet the heat loss of the house. Luckily for most of these homes, this is not the only source of heat. This would be the time to fire the boiler or furnace. Most of these systems will operate in defrost until a sensor in the condensing unit reaches at least 40F, taking much longer if snow is a restriction.

In order to avoid nuisance service calls, be sure to educate your customers on what to do during historic snowfall. If not, you could experience more than just a nuisance. Have you ever had to charge a condensing unit during a blizzard? You guessed it, I have! I looked a little ridiculous out there with my legs wrapped around a tank of R-22. I should have told the poor old woman to not clear the snow away from her condenser with a shovel - she did not realize there was soft copper pipes behind it! If concerned, you may want to recommend to turn on the back-up heat, turning off the heat pump, until after the storm. This way they can clear the snow away from the condenser without issue.

I hope that I learned the hard way so you don't have to!