Let’s talk more about heat pumps. Last time, I explained when to switch to your emergency heat. This time, I want to talk about the defrost cycle.
Heat Pumps
Remember that with a heat pump, we take heat from the outside. The indoor coil becomes the hot coil because the flow of refrigerant is reversed. The outside coil becomes the cold coil.
Cold Coils
If the coil is cold, and it’s cold outside, it will start to frost. When this happens the unit will have a period of defrost time. This doesn’t happen often, and when it does happen it’s usually at night. You might never notice it.
Defrost Cycle
But when it’s snowy or we have freezing rain and it’s really, really cold during the day, we will get calls from customers saying, “Hey, my outdoor unit is making noise and there’s smoke coming off the top! What’s going on?” That’s the defrost cycle in action!
What Happens During This Cycle
When the defrost cycle kicks in the outdoor fan stops, and the flow of refrigerant reverses. Essentially it goes back into air conditioning mode for a brief period of time to get the outside coil hot enough to melt the ice. The “smoke” that you see coming off the top is just vapor, or steam. It’s not smoke, and your unit is doing exactly what it is supposed to do.
Noises You May Hear
It will make some noises you’re not used to hearing, and you’ll see that steam, but there’s nothing wrong with your unit! It’s startling because you don’t normally see or hear this happen. It doesn’t happen often. In fact, it’s possible that your unit hasn’t run a defrost cycle since 2021.
Your Next Step
So if your heat pump starts making strange noises and making steam when it’s really cold out, don’t panic! But any time you have a question or want us to take a look at your system, we are happy to help.