The cold snap playbook: your heat pump in an arctic blast

What normal looks like in deep cold

In a hard freeze a heat pump behaves differently than it does at 45°F, and most of the differences are by design. It runs much longer cycles — possibly close to continuously — because it's sized for our normal climate, not the rare extreme. Supply air feels warm rather than hot, since heat pumps deliver lower supply temperatures than a furnace. Frost forms on the outdoor coil, and every so often the unit pauses heating, may hiss or whoosh, and sends up a plume of steam as it melts that frost off. All of this is normal. What's not normal: no heat at all, ice encasing the whole unit for hours, or grinding sounds from the fan.

The ice rules

A frost coating that comes and goes with defrost cycles needs nothing from you. Solid ice that keeps building is worth a service call — but never take matters into your own hands with an ice scraper, screwdriver, or kettle of hot water. The aluminum fins bend with almost no force, the refrigerant tubing behind them punctures, and hot water refreezes into a worse problem. What you can safely do: brush snow off the top of the unit with a broom, keep the area around it clear so defrost meltwater drains away, and check that snow hasn't drifted against the coil. If the unit sits under a roof edge, watch for dripping that refreezes onto it.

Backup heat: what it is and when to let it work

Most ducted heat pumps here carry backup heat — electric heat strips, or a gas furnace in a dual-fuel setup. The system stages it in automatically when the heat pump alone can't hold setpoint, and during a genuine arctic blast, that's exactly what it's for. You may see a thermostat indicator like 'aux heat' — that's information, not an alarm. Electric backup costs more to run than the heat pump, which is one more reason not to crank the setpoint: a big jump tells many thermostats to skip straight to backup. If your system has no backup and can't hold temperature in an extreme event, space-heat one room, close doors, and call us.

Thermostat habits for the duration

Set it and leave it. Pick a livable temperature and hold it day and night until the cold passes — this is the one week of the year when overnight setbacks genuinely backfire, because recovering from a setback in extreme cold leans hard on backup heat. Avoid 'emergency heat' mode unless the heat pump has actually failed; it's a manual override that runs backup only, at backup prices. Help the system out around the edges: keep interior doors open so air circulates, close curtains at night, and let warm-side rooms share with cold-side rooms. The house may sit a degree or two below setpoint at the coldest hour — that's a sized-for-our-climate system meeting a not-our-climate day, and it recovers.

Common questions