Contrary to popular belief, air source heat pumps work amazingly well in winter, even in very cold climates. But in winter, a heat pump works like an air conditioner in reverse. This means that the heat pump takes heat from the outside air and transfers it to your home. Heat pumps work in winter by extracting heat from outside air (via coolant) and pumping it into your home.
In doing so, they act like an air conditioner, but the other way around. When the refrigerant loses pressure and turns into steam, it is much colder than the outside temperature. Since thermal energy flows from hot to cold (Second Law of Thermodynamics), the coolant collects heat from the outside environment. After the refrigerant absorbs as much heat as possible, the outdoor compressor pressurizes the gas into a hot liquid.
Extremely hot coolant travels to the indoor coils and the blower helps release heat from the coolant to the duct system. Your heat pump will continue to work in cold weather, as long as you buy the right one. Every heat pump is different and you'll need the right equipment to make sure your home can be heated throughout the winter. For UK temperatures, this may not be as big a problem as it could be in some places, such as Canada or North America, where temperatures can drop to -30°C.
As a German manufacturer, Viessmann has tested its heat pumps in the harsh German winter and elsewhere in Europe. However, for five years, Marsik's heat pump kept his family warm even on the coldest days of the year. Inside this heat exchanger, heat is absorbed by a refrigerant, which evaporates and turns into gas. But what will happen to a heat pump if it's really cold outside? There's certainly not enough heat in the winter air, is there? Simply put, the heat pump could extract heat from the air, even when temperatures drop to 25 F or below.
In addition, outdoor temperatures don't usually drop below 32°F during the winter months, so heat pumps are usually able to comfortably heat your home on their own. In fact, the heat pump has a defrost cycle that pumps hot coolant back to the heat pump to melt frost and ice (similar to how the heat pump works in summer mode). For mini-splits, backup heat is usually a type of external heat, such as electric baseboard heaters. There are several different types of heat pumps, such as geothermal and air-to-water heat pumps, however, air source heat pumps are the most common.
When it is very cold outside, you may notice that the outdoor heat pump unit accumulates a layer of ice and frost. Many installers choose to downsize geothermal heat pumps to save on installation costs, which would require the occasional use of backup heat in very cold climates. Now that you know how a heat pump works, you may still be wondering how the system can absorb heat from the ground or air when it is below zero degrees. If you rely too much on backup heat (which can happen if your heat pump is too small), your heating bill will be more expensive than you planned, so it's important to research and find out how big your system should be and when you'll rely on backup heat.