Every winter, we receive calls from customers wanting to know how to tell if their heat pump is functioning properly.

First, let's talk about how your heat pump works:

A heat pump has two stages of heat. The first stage is the heat pump itself. The heat pump provides heating for a space by absorbing heat from the outside air and transferring it to the indoor coil where the indoor blower blows the warm air through the duct system into your living space. If the wall-thermostat sees that the heat pump alone is not sufficient to maintain the set temperature it will activate the second stage of heat, which is generally resistance electric heaters. This is also referred to as "Auxiliary Heat". Most newer thermostats will give some indication when the system is using auxiliary heat.

However, a heat pump that is not operating properly may have a lower-than-normal heat output and depend more heavily on the auxiliary heaters to maintain the desired temperature.

Many customers only become aware that their heat pump is malfunctioning when they receive a high electric bill.

The best way to determine if your heat pump is functioning properly is to test the temperature of the air it is producing:

In normal conditions (approx. 25 degrees and above), a heat pump operating without the assistance of electric heaters should create somewhere around a 15 degree temperature-rise across the indoor coil. For example, if the temperature entering the indoor unit is 68 degrees, the leaving air temperature should be around 83 deg.

You can test this with a simple thermometer. You will need to check the return air temperature and the supply air temperature when the unit is running without auxiliary heat activated.

* If it is possible, it is best to get a comparison of the return air temperature in the house, and the return air temperature at the unit (at the filter). A drastic difference between the two may indicate open ductwork drawing cold air from either an attic or crawlspace.

If the difference between the return and supply air temperature is between 13-20 degrees, that would indicate that the heat pump is operating normally.

If the temperature difference is less than 13 degrees, that would indicate that heat pump is not producing the proper amount of heat and should be checked by a qualified technician.

If the temperature difference is higher than 20 degrees, that would normally indicate low airflow across the indoor coil which could be caused by a clogged air filter, dirty indoor coil or restricted ductwork.