A defrost cycle is a normal heat pump operation. In heating mode, the outdoor coil acts as the evaporator — extracting heat from outdoor air. When outdoor air is humid and cold (between about 25-45°F), frost builds up on the outdoor coil. The defrost cycle reverses the system briefly to melt that frost off.
What you’ll see during a defrost cycle
- Outdoor fan stops
- Compressor keeps running
- Steam rises from the outdoor unit (melting frost)
- Indoor air handler may briefly switch to backup electric heat to compensate
- Cycle lasts 2-10 minutes, then normal heating resumes
Defrost in Colorado mountain installs
In Evergreen, Conifer, or Bailey, defrost cycles are more frequent and longer because of cold humid conditions. Always elevate outdoor units 12-18 inches off the ground on a snow stand — snow accumulation around the unit can flood the base during defrost and freeze solid, damaging the unit.
Steam Rising From Your Outdoor Unit Isn’t a Fire
We get this call regularly: customer sees clouds of steam rising from their heat pump in winter and thinks it’s smoke. It’s just frost evaporating off the coil during defrost. Normal operation. No need to call.
Related: Heat Pump, Cold-Climate Heat Pump.
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Right Way Mechanical is a family-owned HVAC contractor serving Wheat Ridge, Arvada, west Denver, and the Colorado foothills.