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Do Heat Pumps Work in Cold Weather?

heat pump on wall in the snow

Air source heat pumps work at temperatures as low as -25°C

Ground source heat pumps provide consistent heat in all weather

Heat pumps are still three times more efficient than boilers when it’s below 0°C


Heat pumps are a gloriously effective way of heating your home, able to turn electricity into three times as much heat.

But air source heat pumps work by drawing warmth from the air just outside your house – so what happens when winter hits and the temperature takes a dive?

In this guide, we’ll explain how heat pumps keep going through the cold weather, when you should and shouldn’t worry, and what you can do to avoid your heat pump freezing in the winter months.

Want to skip the reading? You can find the best heat pumps for your home by using our custom-built comparison tool. Simply enter a few details, and our professional installers will be in touch with free quotes.

heat pump on wall in the snow

Can an air source heat pump work in cold weather?

Air source heat pumps continue to function when it gets cold outside, and in some cases all the way down to -25°C.

They absorb the warmth that is generated when atoms and molecules move quickly through the air, and that warmth still exists even when the temperature drops below freezing.

Warmth is actually present in all air that has a higher temperature than absolute zero (-273.15 °C), because atoms and molecules continue moving through the air until that point.

Heat pump technology hasn’t quite made it that far – but when you consider that the coldest permanently inhabited place on the planet, Oymyakon in Russia, is -47°C at time of writing, maybe absolute zero isn’t a worthwhile target.

Are heat pumps less efficient when it’s cold?

Air source heat pumps usually lose efficiency as it gets colder, as they have to use more energy to draw warmth from the air.

That’s because these machines need to take in enough warmth to consistently heat up the refrigerant – a liquid with a very low boiling point – until it turns into a gas.

This process requires more power when there’s less warmth in the air. It’s like searching a big, new supermarket for the one item you want – you’ll find it, but it’ll take more effort than usual.

Air source heat pumps start at a high bar though, with the average model producing three units of heat for every unit of electricity it uses – which is three times better than a gas boiler.

This rate falls to around two units when the temperature drops below zero – which is still around two times as much as a gas boiler will produce, per unit of electricity.

You can make your heat pump more efficient with regular maintenance, and by ensuring it has no exposed pipework.

What is the best weather for a heat pump?

Air source heat pumps work best when the weather is hot, as that means there’s an abundance of heat in the air that can be absorbed and used to heat your home.

In hotter locations, you’d generally rather have an air source model than a ground source heat pump, as you’ll be able to take full advantage of temperatures above 20°C.

Under the ground, however, the temperature is always about 10°C lower than that, with very little variation.

This consistency is welcome in cold winters, but less useful when it’s scorching outside.

The best heat pumps for cold climates

If you live in an especially chilly place, your primary concern will be getting a heat pump that can still work effectively all year round.

The answer is to get a ground source heat pump, which is impervious to cold weather, due to its position under the Earth’s surface.

Even when your garden is frozen over, the layers of soil underneath will still be somewhere between 10°C and 13°C, which your heat pump can use to provide your home with plenty of warmth.

If a ground source heat pump isn’t possible for you, don’t worry: the great majority of air source heat pumps are also designed to work in freezing conditions, down to at least -10°C.

That’s more than sufficient for most customers in the UK.

Several heat pumps can even supply your home with warmth when the mercury plummets as low as -25°C.

The best machines with this level of endurance are the LG Therma V, Samsung EHS, Mitsubishi Ecodan R410a PUHZ, and Hitachi Yutaki M RASM-4VNE. You can read more about our recommended models in our annual summary of the Best Air Source Heat Pumps.

The UK has only ever experienced temperatures lower than -25°C on four occasions, and not since 1995, so any of these models should suit you just fine.

And yes, we also wish heat pump manufacturers gave their machines catchier names.

Are heat pumps popular in cold countries?

Heat pumps are extremely popular in cold countries.

In fact, the top four European nations with the most heat pumps per person – Norway, Sweden, Finland, and Estonia, respectively – are some of the chilliest places on Earth.

In Norway, where the average winter temperature is -6.8°C, an incredible one in four people own heat pumps.

And the European countries moving the quickest to adopt heat pumps are Lithuania and Poland – which are also among the coldest, with temperatures often falling below freezing.

Can your heat pump freeze in winter?

Your heat pump can freeze in winter, though if this starts to happen, its defrost mode should automatically activate and stop the spread of ice through its system.

If this doesn’t happen, it means something’s gone wrong.

Possible explanations include broken sensors, low levels of refrigerant, or even that leaves and other debris are blocking the heat pump’s vents.

Top up the refrigerant, make sure the vents are clear and check the sensors. If the machine is still frozen a couple of hours later, contact your heat pump’s manufacturer.

Make sure that the heat pump is truly frozen though – if it’s just covered with snow and ice, that’s normal, and shouldn’t affect its inner workings.

Summary

Your air source heat pump should keep working just fine in cold weather.

However, you’ll probably receive higher energy bills when the temperature drops, as your pump works harder to bring you the same amount of heat.

Ground source heat pumps don’t experience this problem, though they also aren’t as efficient as their air-based counterparts during warm weather.

But in either case, both types of heat pump are at least three times more efficient than gas boilers, all year round.

If you want to take advantage of this higher efficiency, just use our easy-to-use comparison tool. Simply provide a few details about your home, and we’ll pass them on to our expert installers, who be in touch with free quotes.

josh jackman
Josh Jackman Senior Writer

Josh has written about eco-friendly home improvements and climate change for the past three years. His work has featured on the front page of the Financial Times; he’s been interviewed by BBC Radio; and he was the resident expert in BT’s smart home tech initiative.

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