When a heat pump stops working in freezing weather, it usually means the coils are frozen, the system is low on refrigerant, or it has hit its lowest operational temperature threshold and needs backup heat.
Heat pumps don't necessarily "stop working" at specific temperatures, but their efficiency drops significantly as it gets colder.
If your heat pump isn't working, here's a quick list of steps to try before calling for help:
Most heat pumps should complete about two to three cycles per hour, with ten to twenty minutes of downtime between each cycle. If you notice your system cycling too frequently or not enough, it could indicate an underlying issue that needs attention.
The colder it is outside, the harder it is for a heat pump to effectively transfer heat from outside air into your home. Hence, the lower the outdoor temperature gets, the efficiency of the heat pump (presented as COP) drops.
No, You Should Not Turn off Your Heat Pump when It Gets Cold
When it's cold, they pull warm air into the house. Even on a cold day, the heat pump can draw some warmth out of the air, enabling it to generate three to four times the amount of heat as what would have been produced by the same amount of fuel consumed.
It takes time for your home to warm up and cool down. If you're not sure how long it takes, try turning the heating on about 30 minutes before you need it. You should turn it off 30 minutes before you'll stop needing it.
The reality is that it's usually not a good idea to simply keep a heat pump operating all through the night while you're asleep. Instead, you should make sure that you have a programmable thermostat and set it to have it lower the indoor temperatures by 8° to 10°F when people are asleep.
There are two entirely different HVAC concepts known as the "20-degree rule" for heat pumps. The first is a user guideline that suggests setting your thermostat no more than 20∘F above or below the outdoor temperature. The second is an equipment metric referring to the system's "temperature split" or output efficiency.
Your auxiliary heat, or secondary heat source, should come on when your heat pump is struggling to heat your home effectively. The thermostat will trigger auxiliary heat when: The outside temperature is below 40 degrees or a set aux heat trigger temperature. The heat pump is in defrost mode.
9 ways to get the most out of your heat pump all winter
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.
1. The most common signs of compressor failure
In outdoor temperatures above 30 degrees, the heat pump should cycle off and on like a normal furnace. Somewhere between 20 and 30 degrees outdoor temperature, the heat pump will reach a “balance point” where the heat needed by the home is equal to the heat supplied by the heat pump. So now it will run all the time.
This lack of airflow would make it almost impossible for the heat pump to work effectively and could cause it to overheat, break down, or suffer serious damage. Even with sufficient clearance, frost and ice will start to form inside a heat pump when it runs in cold weather.
Is 72 a good temperature for heat in the winter? While slightly higher than the typical energy-saving range of 68°F–70°F, 72°F still offers a reasonable balance between comfort and efficiency.
Is it bad if auxiliary heat comes on? No, it's normal during very cold weather or rapid temperature recovery. Frequent use in mild weather, however, may indicate a system issue.
To check if your heat pump has auxiliary heat, look for an "Aux Heat" or "Emergency Heat" (EM Heat) setting on your thermostat. You can also verify physical electric heat strips in the indoor air handler or look for a secondary furnace (gas/oil) connected to your system.
You don't have to give it a thought or switch anything over on your thermostat. Just leave your heat pump thermostat setting on Heat, and let it do its thing. You may have an aux heat indicator on your thermostat, which tells you when it's on and the electric heat strips or backup heating system are running.
In general, today's most efficient traditional heat pumps can provide 100% heating capacity down to around 32°F and then may start losing heating efficiency. If cold-weather performance is important to you, look for a higher Heating Seasonal Performance Factor (HSPF2) rating.
If your heat pump is unexpectedly expensive to run, the most common culprits are inefficient auxiliary/backup heat, high local electricity rates, or a system that isn't sized properly.
We would normally recom- mend 18–22°C for a com- fortable environment, but if you prefer your home on the warmer side then we suggest the 22°C mark. Setting a higher temperature is not rec- ommended as the heat pump will work hard to achieve this temperature potentially increasing power usage.
If temperatures are near or below freezing, the heat pump may need to run constantly to keep up with the demand. Energy Efficiency: Heat pumps operate more efficiently when they run continuously at lower speeds rather than cycling on and off.
For the most efficient winter operation, set your thermostat to a steady 68°F (20°C) while you are home. Unlike traditional furnaces, heat pumps work best when left alone rather than constantly adjusted. Avoid large temperature "setbacks" (lowering the temp drastically), as this forces the system to work harder to reheat the home.
Outdoor Heat Pump Unit Freezing
One common problem is the outdoor unit freezing when temperatures drop too low. Ice buildup can obstruct airflow, reducing the unit's ability to capture heat. Most heat pumps have a defrost cycle to handle this, which usually solves the problem.