Learn About A Heat Pump’s Defrost Mode

Why Do I Need to Know About Defrost Mode?

During the colder months, heat pumps will perform a “defrost” cycle. Some owners worry that this is a fault because the heat pump suddenly shows some strange symptoms like cooler air coming from the indoor unit, boiling, popping, or snapping sounds, loss of remote control use, and more. However, defrosting is a normal part of the heating operation and is not a fault with the product.

What is Defrost Mode?

During the normal heating mode, the heat pump extracts heat from the air outside and transfers it inside through a coil to warm your home. When the temperature of the outdoor unit becomes too cold and the unit begins to freeze, the sensors on the outdoor unit can detect ice is forming and begin a defrost cycle to melt the frost away.

When this happens, the outdoor and indoor fans stop, but the compressor outside continues to run to help melt the ice away. This mode continues until the temperature of the outdoor unit rises and the ice is melting away.

Why does my heat pump have to do a defrost cycle?

Any ice building up on the outside unit will reduce the airflow across the heat exchanger, and this reduces the efficiency. Defrost mode helps ensure your heat pump runs as efficiently as possible!

How do I tell if my unit is in a defrost cycle?

Inside you will notice the unit will stop heating, the indoor fan will stop, and depending on the model there will be some form of visual indication such as a message on your wall control indicating heat standby or defrost. Some other common and perhaps alarming symptoms include:

How often will my unit go into defrost mode?

There are a number of factors that influence how often a unit will go into defrost mode. Some of these include, but are not limited to:

  • The outdoor temperature and humidity
  • The amount of heating required
  • The condition and cleanliness of the system


Defrost Mode is a completely normal cycle for your heat pump and ultimately ensures the highest level of efficiency.