Heat pump operation when cold question
When heating below 32 °F or 0 °C frost forms on the outdoor coils of a heat pump - and that can happen when the air temperature is above that point, if the coils are that cold to collect heat from cold air.
The controller has some logic which either detects or assumes frost formation and kicks into defrost mode to melt the frost so that airflow is restored. Depending on the unit it may engage resistance heating while doing that.
Water vapor (&quot;steam&quot;) would be an expected side effect from that process.