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Frost or ice on your heat pump: normal or a problem?
On a cold, damp morning a heat pump's outdoor coil turns white with frost, then steams and clears. That is the system working. When the frost turns into a solid block of ice that does not clear, something is wrong.
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NBy Nell Bradshaw, HVAC Guides Editor · Updated September 2026
Quick answerLight frost on a heat pump that clears every 30 to 90 minutes during defrost is normal in a Spokane winter. Solid ice that covers the coil and does not clear, ice building up from the base, or a fan that will not spin means a defrost, airflow, drainage or refrigerant problem. Switch to emergency heat and call.
How defrost works
In heating mode, the outdoor coil runs colder than the outside air so it can pull heat from it. Moisture in the air freezes on that cold coil. Every so often, the control board reverses the heat pump for a few minutes: the outdoor coil warms, the frost melts, and you may see a cloud of steam. The outdoor fan stops during defrost, and backup heat may come on briefly inside. Then it switches back.
That cycle can happen once an hour or more on cold, humid days and much less often on dry, very cold days.
Normal frost versus a problem
Use these as a rough guide:
- Normal: a thin white layer of frost that clears with steam and dripping water.
- Normal: brief whooshing sounds as the valve switches for defrost.
- Problem: solid ice covering the coil, the top or the fan.
- Problem: ice building up from the bottom of the unit.
- Problem: the outdoor fan not spinning while the compressor runs.
- Problem: backup or emergency heat showing on the thermostat all the time.
What causes ice that will not clear
The usual causes are a failed defrost sensor or control board, a reversing valve that will not switch, a failed outdoor fan motor, low refrigerant from a leak, or water that cannot drain away. Melt water that refreezes around the base eventually encases the coil. Gutter water pouring onto the unit and drifted snow blocking airflow cause the same result. A heat pump repair visit tests each of these.
Heat pump stuck in a block of ice?
Call (509) 404-0016Snow, stands and placement
Spokane gets most of its precipitation as winter snow, and severe winters can reach minus 10. A heat pump sitting on a low pad gets buried by drifts and cannot drain its defrost water. Raising it on a stand, keeping it out from under roof edges and clearing snow from around it solves most placement problems. A cold-climate unit installed correctly handles the weather; a poorly placed one fights it all winter.
What to do right now
If the unit is encased in ice, switch the thermostat to Emergency Heat. That runs only the backup heat and protects the heat pump. Do not chip at the ice with a tool, which easily punctures the coil, and do not pour boiling water on it. Clear snow from around the base, check that gutter water is not falling on the unit, and call for service. Our guide on no heat at night covers keeping the house warm while you wait.
Preventing it next winter
A fall heat pump maintenance visit forces a defrost cycle and times it, tests the defrost sensor, cleans the coil and checks drainage under the unit. It also confirms the thermostat's backup heat lockout, which matters for both comfort and the electric bill. For a comparison of heat pump and furnace heat in this climate, see heat pump or gas furnace.
More Spokane heating and cooling guides
Heat pump ice questions
How often should a heat pump defrost?
It varies with weather, often every 30 to 90 minutes on cold, damp days.
Is steam from the outdoor unit normal?
Yes. It is frost melting during defrost.
Can I pour hot water on the ice?
No. It can damage the coil and refreezes quickly. Use emergency heat and call.
Why is emergency heat so expensive?
It runs electric resistance heat only, which costs more per hour than the heat pump.
Should my heat pump be on a stand?
In Spokane, yes. It keeps the unit above snow and lets defrost water drain.
Ice that will not clear? call.
Heat pump repair in Spokane, WA, answered 24/7.
