Why is my heat pump not working in extreme cold weather?

Author: Myrtice Miller  |  Last update: Thursday, January 29, 2026

If you aren't getting enough heat from your heat pump, you should check the outdoor unit first and foremost. Is the outside of the unit casing covered in ice? If so, you may have a broken defrost cycle. As the outdoor unit leeches heat from the air, it creates condensation that then freezes on the outside of the unit.

Is it normal for a heat pump to not keep up in extreme cold?

There are several reasons why your heat pump could be doing this. It could be that your heat pump unit is covered in ice or that it can't endure the freezing outdoor temperature. It could also be that your heat pump is struggling to turn on. Your heat pump not keeping up is an issue you need to resolve ASAP.

Why is my heat pump not working when it's cold?

If the temperature is too low, ice may have gathered on the device. This obstructs airflow and prevents heat absorption. Usually, heat pumps have defrosters which help alleviate this problem. If the defrosters are active, this should be enough to fix the problem.

How cold is too cold for a heat pump to work?

Below 40° f or 5° C the heat pump will frost up and need to turn off to allow the exterior unit to melt. The thing is though, about 10 years ago or longer, heat pumps started to have four-way valves that would switch between cooling and heating.

How can I help my heat pump in extreme cold?

7 Tips for Maximizing Heat Pump Performance in the Winter
  1. Stop cranking up the temperature. ...
  2. Don't rely on emergency heat. ...
  3. Keep your filter clean. ...
  4. Keep leaves and debris clear of your outdoor unit. ...
  5. Do NOT cover your system. ...
  6. Don't worry about the defrost mode. ...
  7. Follow a regular maintenance schedule.

Top 3 Heat Pump ISSUES in Winter!

How to unfreeze a heat pump in winter?

Use a garden hose to spray water over the frozen heat pump components and melt ice. Do not use tools or sharp objects in attempts to chip away ice from coils, as serious damage can be caused. Look for causes of excess ice on your heat pump. Check the air filter and replace it if it is dirty.

Should I turn my heat pump to emergency heat in extreme cold?

Short answer: No. Switching your thermostat to emergency heat or “em heat” just because it's cold outside will just raise your energy bills like crazy. Don't use emergency heat mode unless your heat pump stops heating your home altogether. If that happens, contact a professional heat pump repairman for help.

Can a heat pump be damaged in extreme cold?

As long as your house is properly air-sealed and insulated, an air-source heat pump can perform well beyond temperatures of -13 degrees Fahrenheit!

What is the lockout temperature for a heat pump?

It states that the control for the lockout temperature shall have a maximum setting of 40 degrees F, and set for 32 degrees or less at final inspection.

At what temperature does a heat pump switch to auxiliary heat?

Auixiliary Heat will turn on automatically when heat can no longer efficiently transfer heat from the outside air to heat pump. This is when the outside is around 35-40 degrees and the indoor temperature is around three degrees cooler than the thermostat setting.

How do I know if my heat pump is frozen?

Examine your heat pump to see where ice has formed. Usually, ice will form around the coil but can also form inside the heat pump itself. Judging by the location of the ice, you'll be able to determine some causes of your heat pump freezing.

At what outside temperature does a heat pump stop working?

Some heat pumps lose efficiency when outdoor temperatures dip below 32°F, but they won't completely stop working. Like other heating systems, a heat pump's efficiency depends on your thermostat settings. If you want to keep your home toasty during sub-zero temperatures, you'll lose performance capabilities.

How do I protect my heat pump from ice?

If possible, keep a 2-foot space around the unit clear. Install a cover: Look for a heat pump cover that's durable, weather-resistant, and breathable. This will help protect your unit from snow, ice, dirt, debris, and animals. This cover also provides shade in summer, thereby increasing energy efficiency.

At what temperature is a heat pump useless?

Heat pumps do not operate as efficiently when temperatures drop to between 25 and 40 degrees Fahrenheit for most systems. A heat pump works best when the temperature is above 40. Once outdoor temperatures drop to 40 degrees, heat pumps start losing efficiency, and they consume more energy to do their jobs.

How to tell if a heat pump is low on refrigerant in winter?

Keep reading to learn how to identify this issue in your system.
  1. Gurgling and Hissing Sounds. ...
  2. Not Enough Heating. ...
  3. Frozen Evaporator Coil. ...
  4. Leaking Heat Pump. ...
  5. Uneven Home Temperatures. ...
  6. Ice-covered Heat Pump. ...
  7. Short Cycling. ...
  8. Indoor Parts Won't be Warm Enough.

How to force defrost a carrier heat pump?

If you remove the service panel there is a circuit board. On that circuit board there will be a set of pins labeled forced defrost. By Placing A Jumper Across The Forced Defrost Terminals For 5 Seconds, Or Longer, And Then Removing The Jumper The Unit Will Initate A Defrost Cycle Regardless Of Coil Temperature.

At what temperature does a heat pump go into defrost mode?

When the outdoor coil temperature drops to around 32° F, the thermostat closes the circuit and makes the system respond. This causes an internal timer to start. Many heat pumps have a generic timer that energizes the defrost relays at certain intervals of time.

What causes a heat pump compressor to lock up?

What Can Cause a Frozen Compressor? A clogged air filter that's limiting the amount of air that's moving over the cooling coil. Insufficient refrigerant or too much refrigerant that are causing icy buildup while destroying your compressor.

What temperature should a heat pump set back be?

It means making use of 'setback' temperatures. That is to say, rather than your heating being 'off', the target temperature is just lowered slightly. So at night, you might drop to 18 or 19°C, rather than being 'off'.

Why is my heat pump not heating in extreme cold weather?

If your heat pump is on but not blowing hot air, it could be due to a dirty air filter, low refrigerant levels, or a malfunctioning thermostat. The outdoor unit may also be iced over, or the reversing valve may not be working properly. Contact a professional for further inspection.

How cold is too cold for a heat pump?

Most standard heat pumps will function at 100% efficiency until the outside temperature reaches about 40° F. However, when the temperature dips below this, most heat pumps are not able to maintain efficiency. They become much less effective at temperatures between 20° F to 30° F.

How to unfreeze a heat pump?

How to Defrost a Heat Pump
  1. Turn the heat pump off at the circuit breaker. ...
  2. Next, grab a garden hose and spray the heat pump with water until the ice melts. ...
  3. If it's warm enough, you can reactivate the heat pump and run it on “fan” mode until the ice melts.

What to do with a heat pump in extreme cold?

Most cold-climate heat pumps can run at total capacity until the outdoor temperature gets to about 5 F or below. It will still heat your home at those lower temperatures, but not necessarily keep it as warm as you may typically like. That's where backup heat sources come in.

Will emergency heat defrost a heat pump?

– Will Emergency Heat Defrost Heat Pump? Emergency heat mode bypasses the heat pump, using auxiliary heat sources instead. It does not actively defrost the heat pump but can provide heating if the pump is not functioning correctly due to excessive frost.

Should you turn off your heat pump in extreme cold weather?

Air source heat pumps work efficiently in heating and cooling modes, making them a versatile choice for year-round comfort. Unlike boilers or furnaces, which cycle on and off to maintain a comfortable temperature, heat pumps can run continuously without wasting energy.

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