If you’re asking this question, this is probably the first winter you’ve spent with a heat pump providing comfort for your home. You made a change in spring or winter to your HVAC system and replaced it with a heat pump. This is a great choice—heat pumps are able to deliver excellent cooling in hot weather and energy efficient heating in winter. Thanks to advances in heat pump technology, heat pumps operate in cold temperatures better than ever before.
But making the change to a heat pump brings with it a few adjustments. When you see what looks like smoke coming off the outside cabinet of the heat pump, please don’t panic—this is actually how the heat pump is supposed to run, as we’ll explain below.
The Defrost Cycle of the Heat Pump
First, let’s go into how a heat pump runs. It’s similar to an air conditioner (technically, an air conditioner is a type of heat pump, except it can only provide cooling). It circulates refrigerant between two sets of coils, one indoors and one outdoors. The refrigerant evaporates in one of the coils to absorb heat, and the condenses in the other coil to release heat. In cooling mode, heat in absorb inside and release outside. In heating mode, the process reverses.
This means the outdoor coil absorbs heat during the winter. (Yes, there is always some heat available for the heat pump, no matter the cold.) As the refrigerant evaporates in the outdoor coil, it causes moisture in the air to form along the coil. Do you know the sound of water dripping inside the air conditioner during the summer? That’s the result of the water forming along the indoor coil, then dripping off it. But what happens when moisture forms along the outdoor coil?
If you said, “it freezes,” you’re right. And this presents a problem for the heat pump, since a layer of ice over the outdoor coil will make it harder for the heat pump to draw heat from the air. But a heat pump is built with this problem in mind. Periodically when it is running in heating mode, the heat pump will switch to a defrost cycle. Temporarily, it will reverse the direction of its operation to release heat through the outdoor coil and melt away the ice. It then switches back to heating mode.
It’s Not Smoke, It’s Steam
As the ice melts off the outside coils of the heat pump, it creates steam. This is what you’re seeing coming off the outside cabinet of the heat pump. It may look like smoke, but go outside and put your hand in it and you’ll discover it’s simply water vapor. Your heat pump is working just the way it should.
Is it possible for the heat pump to give off smoke? Yes, but it’s rare. It may indicate a motor burning out. If you discover actual smoke from the heat pump, call a Burlington, VT, HVAC contractor to repair it. We have technicians available for emergency service.
