Short answer: No. Leave your heat pump on when it snows. Turning it off can actually cause more problems than the snow ever will.
Here’s what’s really happening when your heat pump looks like it’s fighting the weather — and the very short list of times you should actually shut it down.
Why the myth exists
Someone at some point looked at a heat pump in January, saw ice on the coil, saw steam rolling off the top, heard the fan stop and the compressor keep running, and thought “that thing is broken, I’d better turn it off before it dies.”
None of that is broken. That’s the machine doing its job.
What you’re actually seeing
Your heat pump has a built-in cycle called defrost mode. Here’s what defrost mode looks like from the outside:
- The outdoor fan stops
- The compressor keeps running
- Steam or vapor rises off the coil
- You might hear a “whoosh” or a hiss from the reversing valve
- The whole cycle lasts about 5 to 15 minutes
- Inside the house, you’ll notice cooler air from the vents for a few minutes
That’s not a malfunction. That’s the system briefly running in air-conditioning mode to melt the frost off the outdoor coil. Once the coil is clean, the system flips back to heating and everything goes back to normal.
If you turn the system off during defrost, you’re stopping it in the middle of solving its own problem. Now you have an iced-over coil and no way to melt it, and when you turn the system back on it will struggle even more.
When you should actually shut it down
There are exactly three situations where turning the heat pump off during snow makes sense:
1. Snow is drifting so deep it’s covering the top of the outdoor unit. The unit needs to pull air through the coil to work. If snow is packed on top of the fan grille, brush it off (gently — don’t shovel into the fins). If you can’t keep up with the drifting, shut the system off at the thermostat and let your auxiliary heat carry the house until you can clear it.
2. The system is running constantly and not making the house any warmer. This means either the auxiliary heat isn’t kicking in when it should, or something’s actually broken. Shut it off, run whatever backup you have (space heaters, fireplace, aux heat if it’s a separate switch), and call us.
3. You hear a metallic grinding or scraping. A fan blade hitting ice, a bearing going out, or something worse. Shut it off at the breaker and call.
That’s the whole list. Cold weather itself, even single-digit weather, is not on the list.
What defrost actually does (and why your heat pump needs it)
A heat pump works by pulling heat out of the outdoor air and moving it indoors. Even at 20 degrees outside, there’s enough heat energy in the air for the system to work — it’s just working harder.
But when the outdoor coil is colder than the air, and the air is humid, water vapor freezes onto the coil. A little frost is fine. A thick layer of ice blocks airflow through the coil, and now the system can’t transfer heat at all.
Defrost mode is how the system melts the ice off. It briefly reverses the flow of refrigerant so the outdoor coil gets hot instead of cold. The ice melts. The fan comes back on. Heating resumes. In our climate, a properly-running heat pump defrosts every 30 to 90 minutes when it’s below about 40 degrees and humid.
What “auxiliary heat” is doing during defrost
If you have auxiliary electric strip heat (most residential heat pumps do), it should kick on during defrost so you don’t feel cold air from the vents. That’s what those strips are for.
Two things to check inside the house:
- On the thermostat, does it say “AUX HEAT” or “EM HEAT” during defrost? AUX is what you want — that means the strip heat is helping. EM (emergency) means the compressor is off entirely and the strip heat is doing all the work. EM should only run if you selected it manually or if the system is throwing an error.
- Is the air coming from your vents warm during defrost? Should be at least room temperature, ideally warmer. If it’s cold air, the strip heat isn’t coming on, and that’s a real problem worth a service call.
The one time cold weather matters
Below about 20°F, a heat pump loses efficiency to the point where the strip heat is doing most of the work anyway. If you have a properly-sized system, this is fine — it was designed for this. If you have an under-sized or old system, you might see your electric bill climb hard during cold snaps.
If you live in a foam-insulated house, this math is different — we wrote about that here.
If your system is over 12 years old and struggling in the cold, it’s worth having someone look at it in September or October rather than during the January cold snap.
Quick FAQ
My heat pump has ice on the outdoor coil. Is it broken? Probably not. Watch it for 15 minutes. If defrost kicks in and the ice melts, it’s working correctly.
The outdoor fan stopped but the compressor is still running. Is it broken? No. That’s defrost mode. Give it 5 to 15 minutes.
Should I put a cover over my heat pump in winter? No. Never. It needs airflow. Manufacturer’s warranties often exclude damage from covered units.
My upstairs stays cold even when the heat pump is running. Should I turn it off and use space heaters? Turn off the heat pump only if you can’t afford the electricity — but call us first, because that pattern usually means duct leakage or an under-sized system, and either is fixable.
How much does it cost to fix a heat pump stuck in defrost? Usually $150–$400 for a reversing valve or defrost board issue. Compressor problems run more. We give the number before we do the work.
Bottom line
Heat pumps are designed for cold weather. What looks like the system fighting the snow is usually the system doing exactly what it’s supposed to do. Leave it running, brush deep snow off the top when needed, and if something looks or sounds genuinely wrong, call us at (423) 637-1846.