Maintenance·5 min read
Steam, frost, and noise: what's normal and what isn't
A field guide to the alarming-but-fine behaviors of a heat pump in winter.
A field guide to the alarming-but-fine behaviors of a heat pump in winter.
A heat pump in cold weather does a handful of things that look like a malfunction to anyone used to a furnace, and don't understand the defrost cycle. Here's what's normal.
Steam or fog rising off the outdoor unit, sometimes dramatically, during a defrost cycle. As the outdoor coil absorbs heat from cold, humid air, moisture condenses and freezes on it. Periodically the system reverses briefly, running hot refrigerant through the outdoor coil to melt that frost, and the resulting steam is completely normal, usually lasting a few minutes every 30-90 minutes in cold, humid weather.
A light, even coating of frost on the outdoor coil between defrost cycles is expected and part of the cycle described above. What isn't normal: a thick, persistent buildup of ice that doesn't clear after a defrost cycle runs, or ice accumulating on the ground beneath the unit from a condensate drain that isn't clearing properly, either of which is worth a service call.
A change in sound when the system switches into or out of defrost, often a whooshing or a brief change in fan pitch as the reversing valve engages, is a normal, if noticeable, part of the cycle. A grinding, screeching, or banging sound is not, and warrants a call regardless of the weather.
