With a cold spell headed our way tomorrow, I thought it would be a great time to talk about one of the most common concerns that we hear about this time of year: frost on heat pumps. Even though you may be alarmed if your outdoor unit appears to have frozen over, don’t panic!
Is it normal to have a frozen heat pump during the winter?
In one word, YES! Heat pumps can ice over during the winter. And it is normal for the entire coil to be covered in a white frost or even a thin layer of ice. When your heat pump is operating in heating mode, moisture from the air can build up on the coil and when temperatures are below freezing, can form some frost or ice. A properly functioning heat pump will then go into a defrost cycle to melt the ice. It is not normal, however, for your entire unit to be totally encased in ice for extended periods of time. If your condenser unit is entirely covered in ice (including the top and sides of the coil) call an HVAC technician.
What happens during the defrost cycle?
Heat pumps have different mechanisms to determine when it needs to go into defrost. Some use mechanical timers while newer systems use temperature sensors. When the system calls for defrost, the reversing valve switches the system into air conditioning mode. This increases the pressure and temperature of the refrigerant circulating through the outdoor coil, causing the ice to melt. During the defrost cycle, a backup heating cycle keeps your home warm until the system has thawed and is ready to operate normally. When the heat pump switches out of defrost you may hear a “whoosh” sound and see a cloud of water vapor rise out of the outdoor unit. The defrost cycle usually lasts between 2 and 10 minutes.
How can you prevent your heat pump from freezing?
One of the main reasons why your heat pump can freeze over when it shouldn’t is restricted air flow. To ensure proper air flow to your system change your air filters regularly and make sure your outdoor coil is not blocked with leaves or snow. Homeowners should also have their heating and air systems serviced twice a year by an HVAC contractor as part of preventative maintenance.