Protecting Heat Pumps from Rain and Snow – GWC Mag

Heat pumps need to be elevated to keep them from being blocked by snow and to allow meltwater produced during the defrost cycle to drain away. Without adequate drainage, the meltwater can refreeze, clogging or damaging the unit. In a previous article, I looked at mounting options, including wall brackets and ground-mounted pads and stands.

While most of the frost that forms on the heat pump’s outdoor coil comes from water vapor in the air, liquid water can also add to the moisture load. The heat pump’s design shelters the coils from vertical rain, but wind-driven rain, splattering raindrops, and blowing snow landing on the coil can increase the frequency and length of defrost cycles.

Under normal circumstances, the extra moisture added by precipitation is modest, as is the impact on performance. But roofs can concentrate runoff from rain and melting snow at drip lines below eaves. Placing a heat pump under an eave can lead to ice buildup on the coil. If the ice becomes too thick, the system may not be able to clear it during the defrost cycle. Airflow drops, as does heat output. If the buildup continues, the system may shut down completely.

Snow sliding off metal roofs also poses a risk. A large mass of snow can bury, dent, or knock a heat pump out of level. In one case I know of, sliding snow ripped linesets out of their fittings, leading to a complete loss of refrigerant.

The best way to avoid problems with sliding snow, concentrated rain, and snowmelt is to keep heat pumps away from eaves and roof valleys, placing them instead on gable ends or under deep overhangs. When this isn’t possible, a protective awning or shield may be needed.

A few years ago, it was difficult to…