Do Heat Pumps Work in Cold Weather, in the UK?

Written-by

Janet Richardson

Reviewed-by

Richard Burdett-Gardiner

Updated on

Sep 05, 2024

Do Heat Pumps Work in Cold Weather, in the UK?

The simple answer is yes, but there are many reasons why. Contrary to what many people believe heat can be extracted from the air outside, even on colder days. That said, it’s also true to say that heat pumps can struggle in extreme temperatures. it may surprise you to learn that the ideal temperature for an efficient heat pump system is cool or moderate.

The Law of Thermodynamics: Heat Pumps in Winter

Heat pumps work by taking advantage of a rule in physics that governs the transference of heat. This phenomenon means energy is neither created nor destroyed and instead energy only changes its state. In simple terms, the law says that energy can't come from nothing, it must come from something or somewhere else. The part that matters to heat pumps is something called heat transference. In nature, heat flows towards cold and vice versa. All heat pump systems need to do then is recreate these conditions and let the laws of thermodynamics do the rest. The heat these systems transfer always comes from one of three external sources.

• Air
• Ground
• Water

Even in the UK, all three of these external elements keep their natural heat radiated by the sun. Air, the least consistent of the trio retains heat even on days we would consider cold. The ground around us and standing water are more consistent as they lose less of their heat to other factors. This is why the temperature of the sea is often warmer than the air around it.

The question we’re asking today is whether the UK climate is suitable for heat pumps, but honestly we can get the answer by looking at another country. It may surprise you to learn that Norway has more heat pumps per home than anywhere else on the planet. With heat pumps providing heating for over six households out of ten, Norway leads the world in this renewable technology. Mind you, the rest of Scandinavia isn’t far behind.

So, if you were wondering whether the UK’s less-than-clement weather hampers heat pump technology, you can guess what we’re going to say.  The truth is heat pumps are more effective in cooler temperatures. As mentioned, residual heat exists in abundance in the UK’s cooler air, ground and water. All it takes is a little bit of electricity to extract, compress, and circulate it. 

Heat pumps are emission-free cost-effective alternatives to traditional central heating. Thanks to the way they work they reduce your impact on the environment because they don’t need combustion to function. Without the need to burn anything, heat pumps produce no emissions. This means less particulates in the atmosphere which is great for our health and our planet. Of course, it’s still possible that the small amount of electricity used to power the system came from a coal or wood-fired power station. However, these days, anyone can source that power from a renewable energy provider.

So, the environmental impact of your system is in your hands. Depending on the type of system, heat pumps can provide heating, hot water, or both. Therefore, how big a carbon footprint your heat pump has, is your call. Now, depending on your circumstances and your location, there may be better options and you may find solar is more efficient. That said, in the UK, heat pump technology is not only viable, but also greener, and can save you money over your old electric, gas, or oil-fired system. Of course, there are many variables to consider which is why we created this guide.  

The Best Conditions for Heat Pumps

The ideal condition for heat pump efficiency is neither too hot nor too cold. This is why they are so popular in Scandinavia and other northern territories. Now, every system has its limit. While most heat pumps work well below zero, their efficiency suffers in extreme cold. In general, when the temperature dips below 15 degrees, the efficiency of your heat pump lessens. At this temperature, your system will begin to match traditional central heating. Indeed, in colder countries, heat pumps are often paired with other heating systems. Teaming up with a gas-fired or electric heating system allows a heat pump to function as thermometers plummet.

When the temperature gets too high, heat pumps have an extra trick in their pipes. Thanks to the laws of thermodynamics some heat pumps can function in reverse and cool a house instead of providing heat.

When it comes to climate and weather the sole real issue heat pumps can struggle with is heating colder or poorly insulated houses. If your home is older or lacks decent insulation, most heat pumps will struggle to reach and maintain a comfortable temperature. In simple terms, heat pumps are better at reaching and maintaining a comfortable temperature than trying to heat a cold house fast.

If the property loses heat too fast, the system will struggle to reach the desired temperature. This is why northern countries like Norway, Denmark, and Finland invested so heavily in heat pumps. Their colder climates mean that good insulation is a must when building properties. In the UK climate though, insulation isn't such a high priority. This is the area heat pumps struggle with the most.

In general, most climates suit heat pumps, because it’s easy to extract the surrounding heat and turn it into central heating. They work well as heaters in cooler countries and air conditioners in hot countries. So, wherever you live, a heat pump is a sound investment.
Now, not all heat pumps are equal, some work better in colder climates than others. We’ll discuss this in the next section, but the reason often comes down to where they source their heat.

If you have an air source heat pump then during cold weather and the winter months the exposed piping may mean it needs to work harder to heat your home. As you’d expect though, even in situations like this there are options you can add to improve the efficiency of your system.

If the heat pump system struggles to find enough warmth from the air, then you can add a supplementary system. These 'hybrid heat pumps', are more expensive to install and run, and can lead to increased energy bills. They’re not the ideal solution for everyone as for most folks, saving money is often the key reason for getting a heat pump. However, even with higher bills, these systems can still lessen your carbon footprint and make a big environmental impact. It’s worth noting though, that hybrid heat pump systems using gas, oil, or LPG boilers won’t be eligible for the Government’s Boiler Upgrade Scheme. 

Any heat pumps with exposed piping tend to be much more at risk in colder weather. If your system has well-insulated pipework or, better yet, underground piping, there's less call for a hybrid system. In the next section, we’ll look at the best models for cold weather conditions.

Which Heat Pumps Work Best in Cold Weather?

In general, ground source (geothermal) heat pumps make the best cold-weather heat pumps. Ground source heat pumps work best because the ground heat protects their underground arrays from the elements. The ground has a natural and constant supply of warmth, which is how ground-source heat pumps work.  This residual heat also protects the pipes where it extracts its heat. There are two types of ground source heat pumps and although they work in the same way, one is better at coping with the cold than the other. The variants are:

• Horizontal matrix
• Deep bore

Horizontal matrix: as the name implies uses a horizontal network of pipes laid in the ground. This pipework lies a metre or so under the earth and can vary in size between a few square metres and the size of a football pitch. Buried just below the surface, these arrays are more prone to ground frost than their deep-bore cousins. Although, more likely to freeze than a deep bore system, it would take extreme weather conditions before the system stops working.

Deep bore: unlike their less expensive horizontal alternatives, deep bore heat pumps use a vertical pipe to extract heat. These holes and the pipes that fill them can be a hundred metres deep. Their depth protects them from ground frost, so deep bore heat pumps seldom freeze. b They are far more expensive to install, though, and God forbid something did go wrong they are much harder to repair.

Both ground source heat pumps offer some protection against freezing. So, while frozen pipes are not impossible, they're unlikely. This is because the ground generally holds heat longer than the air around it.

The upshot is, these systems won't lose much efficiency over a year. Air source heat pumps, by contrast, are prone to extreme weather conditions because their pipes live outside.

Why do Air Source Heat Pumps Lose Efficiency in Cold Weather

The amount of heat an air source heat pump can transfer to your home depends on the outdoor temperature. When the temperature outside drops below 0°C, it affects the overall heat output of the air source heat pump.

The heating capacity of air source heat pumps also drops as the outside temperature decreases. However, a typical system can provide 100% of the heat you need each year.  

Most air-source heat pumps have ratings that mean they work well until the outside temperature falls under -5 degrees Celsius. Below this point, they lose efficiency. Most modern air source heat pumps will be able to heat your home down to -15°C and some models can still provide some heat at temperatures below -22 degrees Celsius. You can check your rating with your manufacturer. 

If you live in an area where temperatures like this are common, it’s a good idea to have a backup heating source for those cold winter days and nights. This way, your backup system can carry you through those colder times and pick up the slack when your air source heat pump lets you down.

If your home isn’t hooked up to the gas mains, electric mains, or other forms of conventional heating, you can always opt for something like a wood burner. They offer a low-cost alternative to fitting a hybrid system and are more than capable of backing up your air source heat pump when needed.

Do Heat Pumps Work in Freezing Temperatures?

First up don’t panic. Any weather event capable of knocking out a heat pump would cause mayhem for any heating system. Air source heat pumps can suffer in extremely cold weather, and it is normal for the piping and pumps to freeze up. Most systems come with fail-safes in mind, and they should withstand most temperatures.

That said, should the worst occur there are some things you can do. Heat pump pipes are well insulated. If you think they need it, you can even add extra cladding to compensate for the freezing cold. It’s a good idea to make sure your system is well maintained too and the best time to do this is long before the weather turns. One thing you should never do is add antifreeze into frozen pipes, as it’s likely to make things worse.

Most decent heat pump systems have a ‘defrost setting’ designed to kick in when the temperature drops.  In this mode, the system changes how it uses energy and diverts most of it towards thawing the ice around the piping. These days, defrost mode should start automatically when it detects ice. However, if you’re unsure, it’s a good idea to consult the owner’s manual to see if this is something you’ll need to do yourself. If this doesn’t help for any reason, call the supplier of your heat pump and get their advice. Never try and fix the situation yourself, heat pumps are complex machines, and you should always seek professional advice.

So, can Heat Pumps Cope with the UK’s Cold Weather?

Heat pumps can effectively cope with the UK's cold weather. Modern heat pumps are designed to operate efficiently even in freezing temperatures, making them suitable for the UK's relatively mild winters. Ground-source heat pumps, which draw heat from the ground, maintain consistent performance through the year. Air-source heat pumps, while slightly less efficient in very cold conditions, have advanced significantly, with many models featuring enhanced defrost cycles and improved refrigerants to maintain efficiency.

The key to their effectiveness lies in proper installation and adequate insulation of homes. Well-insulated properties require less energy to heat, allowing heat pumps to operate more efficiently.