Home All things HVAC, General Contracting, etc Why is my heat pump steaming??

Why is my heat pump steaming??

A common question from the residential sector. If you are experiencing or noticing periods where your heat pump (outdoor) is generating clouds or puffs of steam/vapor during the heating season you can relax. During periods of mechanical heating (heat pump operation during heating) your outdoor heat pump utilizes a defrost logic board. This board typically will go into a cycle called defrost if the defrost thermostat is closed and the required amount of time has been met. During this defrost cycle the outdoor fan will stop, the reversing valve returns to the cooling position and your aux heat is enabled to temper the air temperature indoors during the defrost cycle. This cycle will last until either the defrost thermostat has opened or a preset amount of time has expired. As your system exits the defrost cycle the outdoor fan will come on again and the reversing valve will return to the heating position (many times this can create a noticable “swishing” sound, and because the outdoor coil heats up during the defrost period to melt any ice build up many times it will create a vapor cloud during milder ambient temperatures due  the warm moisture from the freshly defrosted coil attempting to condense again once the fan pushes it into the cooler ambient air surrounding the heat pump.  Once outdoor temperatures reach lower temps (20-30) this occurance of “steam” occurs less often as colder air contains less moisture.

So relax and know that if your experiencing the above described “symptoms” it is only normal defrost cycling as needed. Units will vary in how they intiate and terminate defrost however the concept is the same across the board.


This article was submitted to us by Cardinal Air Services

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