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Defrost

Defrost is the cycle in which a heat pump briefly reverses to melt frost off its outdoor coil.

Editorial staffEdited by heatpumpwiki

History 1

Defrost is how an air-source heat pump clears frost from its outdoor coil in heating mode. NRCan: "the reversing valve switches the device to the cooling mode. This sends hot gas to the outdoor coil to melt the frost. At the same time the outdoor fan... is shut off."Source 1

Controls start defrost on a timer ("every 30, 60 or 90 minutes") or on demand when sensors detect frost.Source 1 Lennox describes cycles "lasting 5 to 15 minutes," and says steam from the outdoor unit "is a normal occurrence."Source 2 See Heat pump defrost cycles.

Sources

  1. 1.Heating and cooling with a heat pump. Natural Resources Canada. Accessed Oct 25, 2026
  2. 2.Heat Pump System Information, User Guide (507657-01). Lennox. Accessed Oct 25, 2026

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