Move heat from outside to inside, with a heat pump!

Heat Pump Minimum Outside Temperature in the UK

Written-by

Janet Richardson

Reviewed-by

Richard Burdett

Updated on

Dec 31, 2025

Read Time : 4 Minutes

Heat Pump Minimum Outside Temperature in the UK

Investing in a heat pump could be one of the best decisions you ever make. After all, they are incredibly cost effective, energy efficient, and they produce far less emissions than conventional forms of heating. While the initial costs for purchase and installation can seem a little intimidating at first, there are some great government schemes available, and you are sure to make some great savings on your energy bills.

It is important to know as much as possible about heat pumps before you go to purchase them, and this page will take you through the minimum outside temperature in which they can operate efficiently.

Heat Pumps in Cold Weather: Myths vs Facts

Myth	Fact
Heat pumps don’t work in cold UK weather	Heat pumps are designed to work efficiently in the UK climate and can extract heat from the air, ground, or water even in freezing conditions.
Heat pumps stop working below 0°C	Most modern air source heat pumps operate effectively down to around -15°C, and some models continue to provide heat at -20°C to -25°C, though efficiency may reduce.
Heat pumps are only suitable for warm countries	Heat pumps are widely used in colder countries such as Norway, Sweden, and Finland, where winter temperatures are often far lower than in the UK.
Air source heat pumps freeze and fail in winter	Modern systems include automatic defrost cycles that prevent ice build-up and allow reliable winter operation.
You always need a separate backup heating system	Most UK heat pump systems include a built-in electric backup heater that only operates during very cold periods or high demand.
Ground source heat pumps are affected by cold weather	Ground temperatures remain relatively stable year-round, allowing ground source heat pumps to maintain consistent efficiency even in winter.
Heat pumps can’t heat older UK homes	Older homes can use heat pumps successfully if they are well insulated and correctly sized, sometimes with radiator upgrades or high-temperature models.
Heat pumps are inefficient in winter	While efficiency drops slightly in colder weather, heat pumps still typically deliver 2–4 units of heat for every unit of electricity used.

The Best Weather for Heat Pumps

It should be noted that the optimal climate for heat pumps are ones that are warm or moderate. This is because the pumps work by extracting the heat from the surrounding air and converting it into energy. However, heat pumps are specifically designed to operate efficiently in cooler climates such as the UK, where usable heat is still present in the air, ground, or water even at low temperatures. So, the warmer the climate, the more heat can be extracted. Of course, the fact that heat pumps can be used as forms of central heating and air conditioning also comes in pretty handy.

Some heat pumps are able to function better in colder climates than others, something which should be kept in mind. The air source heat pump is less likely to function efficiently in colder weather because of the exposed piping. That said, modern air source heat pumps are designed with advanced defrost cycles and inverter technology to maintain performance in winter conditions. As a result, the heat pump will need to work extra hard in order to remove any ice that has formed in or outside of the system. On the other hand, ground source heat pumps will tend to work effectively in cold weather because they have been buried underground where there is a constant supply of natural warmth.

If your heat pump system is not able to get enough warmth from the surrounding air, a supplementary system will need to be implemented to keep things going. In practice, many UK systems rely on built-in electric backup heaters rather than separate external heating systems. While this can lead to an increase in your energy bills for a short period of time, you will have a form of backup heating that can pick up the slack when the Air source heat pumps starts to lose efficiency. Air source heat pumps are much more at risk of inefficiency in cold weather due to the exposed piping, especially when compared to the concealed ground source heat pumps.

In the next section, the reason for the loss of efficiency found in air source heat pumps during cold weather will be further explained.

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Why Air Source Heat Pumps Lose Efficiency in Cold Weather

The amount of heat that an air source heat pump is able to transfer to your home is quite largely reliant on the outdoor temperature. As this starts to drop, the overall heat output of the air source heat pump does so with it. The heating capacity of the air source heat pump will also tend to decline as the outside temperature decreases.

The air source heat pump is typically sized to be able to provide heat for the majority (often around 85-95%) of a household’s annual heating demand, not necessarily peak demand on the coldest days. When the temperatures are above freezing, it should be able to fill most or all of the heating requirements for your household. As a result, it is highly recommended that you invest in a form of backup heating that is readily available for when the outside temperature drops. In most domestic systems, this backup is an integrated electric immersion or resistance heater rather than a separate fuel-based appliance. This way, it can pick up the slack when your air source heat pump starts to decline in power and efficiency.

If you don’t want your home hooked up to the gas mains, electric mains, or other forms of conventional heating, portable gas heaters or solid-fuel appliances may be used as occasional backup, but these are not commonly recommended as primary supplementary heating solutions due to safety, ventilation, and emissions considerations.

Minimum Operating Temperatures for Heat Pumps

This is not always a simple question to answer. The minimum temperature at which a heat pump can operate efficiently can vary according to the quality of the pump system you have installed. For brands and models that are at the lower end of this, the temperature at which the unit is no longer able to extract heat efficiently tends to be around -10°C to -15°C. For the brands and models that are towards the higher end, you can expect the efficiency to stop at around -18°C to -22°C.

You may even be lucky enough to find models that will remain efficient up to -25°C. However, with systems that fall into this category, it is important to note that they usually use an auxiliary heater to maintain output at very low temperatures, which can reduce overall system efficiency. So, while this allows the pump to continue working to heat your home, it is not always a cost-effective option. Of course, this is more in reference to air source heat pumps than ground source ones. This is because the former of the two is installed outside where it is exposed to the air and elements. The latter is fitted underground, where temperatures are more stable year-round, but also where it is surrounded by the natural warmth the ground produces.

Do Heat Pumps Work in Freezing UK Conditions?

Heat pumps are well suited to the UK’s climate and can operate efficiently even in freezing temperatures when correctly specified and installed. While air source systems may lose efficiency in extreme cold, modern designs and proper insulation ensure reliable performance year-round. Choosing the right system for your property is key to maximising efficiency and savings.

Want to Know More?

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