On a damp, chilly day in Schomberg, a little frost on an air-source heat pump’s outdoor coil can look alarming. Often, it is part of normal heating operation. The useful question is whether the frost clears and the house stays comfortable.
Why does the outdoor unit frost up?
In heating mode, an air-source heat pump takes heat from outdoor air. Moisture can freeze on its outdoor coil when conditions are cold and damp. Frost reduces heat transfer, so the equipment periodically runs a defrost cycle to clear it. Natural Resources Canada explains that the cycle temporarily directs heat to the outdoor coil. The outdoor fan may pause, and some systems use supplemental heat indoors during that period.
What can be normal?
- A light coating of frost appears and later clears.
- The outdoor fan briefly stops during defrost, then resumes.
- Meltwater drips beneath the outdoor unit. Keep an eye on where it drains so it does not refreeze on a walkway.
- The indoor airflow or temperature changes briefly, then your home returns to its usual comfort level.
Defrost behaviour varies by system and weather. Your equipment manual is the best reference for what its controls and indicator lights mean.
When should you call for help?
Arrange a professional assessment if heavy ice remains on the outdoor unit, the unit appears stuck in defrost, the house cannot reach the thermostat setting, or unusual noise develops. The U.S. Department of Energy’s homeowner heat pump guide lists persistent ice and failure to maintain the set temperature among signs that need a qualified technician. If the system is your main heat source and the house is becoming too cold, call promptly.
Do not chip ice from the coil or open electrical panels. Those steps can damage equipment or expose you to hazards. A technician can check airflow, controls and the unit’s operation safely.
What to check before you call
- Confirm the thermostat is set to heat and note the room temperature and setting.
- From a safe position, note whether the frost clears after the unit runs. A short video can help describe what you saw.
- Look for loose leaves or snow blocking the space around the unit. Follow your manufacturer’s guidance for keeping its airflow clear; leave ice on the equipment to a professional.
- Tell the service team when the problem began, whether heating recovered, and any error code shown on the thermostat or indoor unit.
For an assessment, see our heating and cooling services or call (905) 939-2350. Please call rather than relying on the website form while its email delivery is being restored.
Sources: Natural Resources Canada: Heating and cooling with a heat pump; Natural Resources Canada: Air-source heat pumps; U.S. Department of Energy: You Installed an Air Source Heat Pump. Now What?