Do Air Source Heat Pumps Work in Winter in the UK?

Yes, air source heat pumps continue to work in winter and in cold temperatures in the UK. Even when the temperatures drop, these systems are designed to keep working and provide warmth for your home.

While their efficiency generally does decrease as the temperature declines, they remain a reliable source of heating during the winter months. In fact, air source heat pumps are able to work at temperatures as low as -25°C (which is much colder than anything the UK is likely to experience).

That said, you should be aware that your energy bills may rise slightly in the coldest periods, as the system works overtime to maintain a comfortable indoor temperature. In this article, we’ll break down exactly how air source heat pumps work during winter and in colder conditions, so you can get the best performance from your investment.

Want to jump straight ahead? Complete the form below to receive a free air source heat pump quote today:

Do Air Source Heat Pumps Work in Cold Weather?

As we touched on earlier, air source heat pumps are fully capable of operating throughout the winter and in colder weather. In fact, many modern heat pumps can function in temperatures as low as -25°C which is far colder than anything you’re likely to see here in the UK. This means that even during a very chilly British winter, you can rely on your heat pump to keep your home warm and comfortable.

That said, it’s important to understand that the efficiency of an air source heat pump does drop when outside temperatures fall. This happens because the pump has to work harder to extract heat from the colder air. The colder it gets outside, the less heat there is available for the pump to absorb, so it uses more energy to maintain the same level of warmth inside your home.

Despite this decrease in efficiency, air source heat pumps remain a reliable heating option even during cold snaps. They’re also growing in popularity as more people take advantage of the Boiler Upgrade Scheme which offers a £7,500 grant towards the cost of installation, making air source heat pumps much more affordable.

How Does an Air Source Heat Pump Work in Winter?

The way an air source heat pump works in winter is actually pretty straightforward. It pulls in outdoor air and uses a special refrigerant that can absorb heat at low temperatures. This refrigerant is then compressed, which makes it even hotter, and the heat is released inside your home.

The system also has built-in features like a defrost cycle (more on this shortly) to prevent ice build-up and an electric heating element to stop water from freezing inside the unit, so it keeps running smoothly.

For ease, here’s how an air source heat pump works in cold weather:

• Pulls in cold outdoor air and absorbs its heat using a refrigerant.

• Compresses the refrigerant to increase its temperature and releases the heat inside your home.

• Uses a defrost cycle to melt any ice that forms on the outdoor unit, keeping it efficient.

• Activates an electric heating element if needed to prevent freezing inside the system.

• Continues to operate even in subzero temperatures, though it may use a bit more electricity to keep your home warm

What is a Defrost Cycle?

When your air source heat pump is running in winter, you might notice that frost or ice sometimes builds up on the outdoor unit. This is completely normal and happens because the pump is pulling heat from cold, damp air. To keep things running smoothly, the heat pump has a built-in feature called the defrost cycle. This cycle automatically kicks in when the system senses that ice is forming, melting away the frost so your heat pump can keep working efficiently.

The defrost cycle works by briefly switching the heat pump from heating mode to cooling mode. During this time, the flow of refrigerant is reversed, sending warmth to the outdoor unit to melt the ice. The outdoor fan usually stops to help the process along and you might see a cloud of steam as the ice melts away. This is perfectly normal. The whole process only takes a few minutes, and once the ice is gone, your heat pump goes back to heating your home as usual.

Alongside the defrost cycle, your heat pump also uses an electric heating element to prevent water from freezing inside the unit during very cold weather. This heating element automatically turns on when temperatures drop low enough, helping to keep any condensation or water in the base tray from turning to ice. Both the defrost cycle and the electric heating element work together to protect your air source heat pump and keep it running efficiently.

How Efficient is a Heat Pump in Winter?

As we’ve discussed, air source heat pumps do lose some efficiency in winter, but how much they lose can vary. There isn’t a single answer that applies to every heat pump, as performance depends on the model, the outdoor temperature and how well your system is maintained. Generally, as it gets colder, your heat pump needs to work harder to extract heat from the air, which means it uses more electricity and its efficiency drops.

To get a clear idea of a heat pump’s efficiency, you should look at its Seasonal Coefficient of Performance (SCOP). The SCOP is a measure of how efficiently a heat pump operates over an entire heating season, taking into account all the temperature changes between warmer and colder months. A higher SCOP means the heat pump provides more heat for each unit of electricity it uses, giving you a better sense of its real-world performance throughout the year.

For example, the Vaillant aroTHERM plus, which we offer, has a high SCOP, up to 5.03. This means that, on average, it can deliver just over five units of heat for every one unit of electricity consumed over the heating season. In practical terms, this level of efficiency means lower running costs and less energy wasted.

What is the Best Temperature for a Heat Pump?

Air source heat pumps perform at their best when the weather is mild or warm, simply because there’s more heat available in the air for them to extract. The warmer it is outside, the less effort your heat pump needs to put in to bring that heat indoors. This means the system runs more efficiently and uses less electricity to keep your home comfortable.

Since the UK generally has a mild climate, and with our summers becoming noticeably warmer each year, it’s an ideal place for an air source heat pump.

However, while temperature is important, it’s not the only thing you should think about when considering a heat pump for your home. It’s just as crucial to make sure your home is actually suitable for an air source heat pump. Factors like available outdoor space, insulation and planning permission requirements all play a part in determining if a heat pump will work for you.

What Problems Could an Air Source Heat Pump Face in Cold Weather?

As we've established, while air source heat pumps are designed to handle cooler temperatures, there are a few common issues that can occur during the colder months. Understanding these potential challenges can help you keep your heat pump running smoothly and avoid any surprises when winter arrives:

You might notice your electricity usage goes up

When the temperature drops, your air source heat pump has to work harder to pull heat from the cold air outside. As a result, you may see your electricity bills rise during the winter months. This is normal, but it’s something to keep in mind when budgeting for your home’s heating costs.

Your heat pump can become less efficient in the cold

Air source heat pumps are most efficient in milder weather. When it gets really cold, the system has to put in extra effort to extract heat, which means it won’t run as efficiently as it does in warmer conditions. While it will still heat your home, you may notice it takes a bit longer or uses more energy.

The outdoor unit could get blocked

Snow, ice or even fallen leaves can sometimes block the outdoor unit of your heat pump. If the airflow is restricted, your system won’t be able to work properly and could even shut down to protect itself. It’s a good idea to check the unit regularly and clear away anything that might be in the way.

Frost can build up on the outdoor unit

On especially cold or damp days, you might see frost or ice forming on the outside part of your heat pump. While a little frost is normal, too much can stop your system from working efficiently. While most heat pumps have built-in features to deal with this, such as the defrost cycle, it’s still something to watch out for.

You may notice the defrost cycle running more often

When frost or ice does build up, your heat pump will automatically switch into a defrost cycle to melt it away. In colder weather, this can happen more frequently. While it’s a normal part of how your system works, you might notice a brief pause in heating while the defrost cycle is running.

Your system might blow cool air instead of warm (for air-to-air heat pumps)

If you have an air-to-air heat pump, you might occasionally feel cool air coming from your vents during the winter. This usually happens when the system is in defrost mode as it temporarily stops heating your home to clear away ice from the outdoor unit. The warm air will return as soon as the defrost cycle is finished.

Your radiators might not feel hot enough

With air source heat pumps, especially air-to-water systems, your radiators may not get as hot as they would with a traditional gas or oil boiler. If your heat pump is sized and set up correctly, and rooms aren’t warming up as expected, it could be due to closed radiator valves, incorrect thermostat settings or needing to adjust your heating schedule for longer, gentler heating periods.

At Glow Green, we are proud to install the Vaillant aroTHERM plus range, a popular and reliable air-to-water heat pump.

What is the Best Air Source Heat Pump for Cold Climates?

As we’ve discussed, the UK’s climate is generally well-suited for air source heat pumps. Most modern models are built to operate efficiently even in extremely low temperatures, much colder than what we actually experience here. So, for most people, there’s little need to worry about whether a heat pump can handle a typical British winter.

However, if you live in a particularly chilly part of the UK, like the North or rural Scotland, or you’re especially concerned about cold weather performance, it’s worth considering the Daikin Altherma 3H HT. It’s been ranked as the best air source heat pump for cooler climates in our guide.

Though, it’s worth noting that if you’re comparing different types of heat pumps, ground source heat pumps actually perform best in winter. That’s because the temperature underground stays steady all year round, providing a consistent source of heat.

The downside to ground source heat pumps is that installation can be expensive and often isn’t practical for many UK homes, especially if you don’t have enough outdoor space. For most people, an air source heat pump remains the more accessible and cost-effective choice.

Top Tips to Keep Heat Pump Operating Efficiently in Winter

Here are some top tips to help you keep your air source heat pump running efficiently throughout the winter:

• Keep the outdoor unit clear of debris: Make sure there’s nothing blocking your heat pump’s outdoor unit. Remove leaves, snow, ice or dirt regularly to maintain good airflow and prevent the system from working harder than it needs to.

• Clean or replace filters regularly: Dirty filters restrict airflow and reduce efficiency. Check your filters every 1 to 3 months and clean or replace them as needed to keep your heat pump performing well.

• Set a steady, comfortable temperature: Avoid constantly changing your thermostat. Instead, keep it at a consistent temperature to reduce strain on the system and save energy. Using a smart thermostat can help you manage this easily.

• Monitor and manage frost or ice buildup: Keep an eye on your outdoor unit for frost or ice. Most heat pumps have automatic defrost cycles, but if you notice excessive ice or the system isn’t defrosting properly, it’s best to call a professional.

• Check and seal any ductwork or pipe insulation: Ensure your ducts and pipes are properly sealed and insulated to prevent heat loss which helps your heat pump work more efficiently during cold weather.

• Schedule an annual professional service: Having a qualified technician inspect your heat pump each year can catch small issues before they become costly problems. You can read our guide on air source heat pump maintenance for more information.

• Clear snow and ice promptly: If there is heavy snowfall, gently brush away snow or ice from the outdoor unit to keep it clear and functioning properly. Avoid using sharp tools that could damage the unit.

Key Takeaways

✔ Air source heat pumps keep working reliably throughout the UK winter, even when temperatures drop below freezing.

✔ You may notice your heat pump becomes less efficient as it gets colder outside, since it has to work harder to extract heat from the air.

✔ Most modern heat pumps are designed to handle much lower temperatures than you’ll typically see in the UK so you don’t need to worry about them stopping in cold weather.

✔ During winter, you might see a slight increase in your electricity usage, as the system uses more energy to keep your home warm.

✔ Features like defrost cycles and electric heating elements help your heat pump run smoothly and prevent issues like frost buildup, even on the coldest days.

✔ For the best results, make sure your system is well-maintained and your home is properly insulated. This helps your heat pump stay efficient all season long.

✔ The UK’s mild climate makes it an ideal place for an air source heat pump. If you’re considering one, it’s a good idea to reach out to a trusted heat pump installer, such as Glow Green, for expert advice and installation.

Do Air Source Heat Pumps Work in Winter FAQs