Is That Smoke Coming from My Unit?


An odd characteristic of a heat pump in the winter season that causes concern is “smoke” rising out of the outdoor unit. I’ve known customers to call the fire department when they witness this. The “smoke” they see is really steam and is a byproduct of the defrost cycle a heat pump goes through on occasion during the heating cycle.

A complete defrosts cycle on a heat pump looks like this:

1) The outdoor fan will stop turning while the compressor down inside the heat pump continues to pump refrigerant.

2) The flow of the refrigerant will reverse direction resulting in a loud “SWOOOOOSH” coming from inside the heat pump… this is when the steam cloud starts to rise up out of the heat pump.

3) The frost will melt away while a thermostat down inside the heat pump monitors the progress.

4) Once all of the frost is gone, the thermostat will close and the fan will restart. The refrigerant flow reverses back to the heating cycle resulting in another loud “SWOOOOOSH.” This will complete the defrost cycle.

If your heat pump develops a solid sheet of ice that never seems to go away, the defrost cycle is probably not working correctly. This will increase your utility bills and possibly damage the heat pump. If you suspect your heat pump is not defrosting properly, call (757) 656-3023​​​​​​​ to schedule a service call and we will dispatch a technician to assist you.