How Do Air Source Heat Pumps Work In Winter? Everything You Need to Know


Heat pumps are becoming a more effective way of heating your home, and a lot of people are looking to get them installed.

But if you're planning to install an air source heat pump, you might be wondering if it's going to work in colder climates because they work by drawing warmth from the air outside your house.

We've unpacked everything you need to know about how air-source heat pumps work in winter to help you make the most of your heating system.

What are air source heat pumps?

An air source heat pump is a heating system that converts air to water. The converted air is then heated using a heat exchanger and fed into a hot water tank for household use or to heat underfloor heating and radiators.

Heat pumps are a more energy-efficient and environmentally friendly central heating system when compared to your standard boiler central heating systems.

How does an air source heat pump work?

One way to describe an air source heat pump is to call it a reverse refrigerator.

Instead of keeping things cool inside and pumping the warm air outside, the air from outside is drawn in and used to warm water which in turn warms the home.

More accurately, the air is drawn over a set of tubes filled with refrigerant. This process causes the refrigerant to heat up and converts it from a liquid into a gas.

The gas is then sent through a compressor, increasing the pressure and generating more heat.

These heated gasses then enter a heat exchanger, surrounded by cool air or water. The gasses transfer their heat to this water or air, heating it. This is then circulated through your home, warming it up, or it gets stored in a water tank to be used later.

Through this process, the refrigerant gases cool, turning back to the water and beginning the cycle again.

Do air source heat pumps work in winter?

Do air source heat pumps work in winter

The short answer: yes!

The longer answer is that, while older heat pumps were significantly less efficient and effective in cold climates, the technology and design of new heat pumps have advanced greatly. More modern heat pumps work brilliantly in cold weather and are significantly more efficient than traditional heating methods.

The key improvement factor is the modernised compressors found in the new heat pumps. These compressors can automatically adjust to temperature changes, increasing their speed and energy consumption on particularly cold days and reducing it on warmer days.

Combined with all the improvements added to the other parts, you've got an excellent heat pump that will keep your home warm while saving you money and energy.

Common misconceptions about air source heat pumps

If you have been accustomed to oil and gas heating systems, you're likely used to a system that can work quickly and heat your house fast. Unfortunately, this is often due to the systems installed being bigger than necessary and thus quite inefficient in the long term.

A modern air source heat pump, if installed correctly and maintained properly, can heat a house at a slightly slower rate but then maintain an even heat for an extended period without costing you much.

When you want to heat the house faster, you'll push up the thermostat, which will cause electric heating to kick in, having a big impact on your electric bill. To avoid this problem, you can install a lockout thermostat and relay with the system to reduce any other electrical use.

Some systems are badly designed with poor ductwork, resulting in cold drafts and unwanted air noise.

Errors with the defrost system can cause a cold draft when the unit starts to defrost mode and can temporarily convert the system into a cooling system. This can be fixed with some basic maintenance.

Protecting your air source heat pump from harsh weather

Here are a few ways to prevent your air source heat pump from being negatively affected by the harsh winter storms:

Keeping a 2-foot (60cm) clearance around the unit will help to improve airflow and prevent extra snow build-up in colder climates. Be sure to turn the unit off when you clean around it. If you're clearing snow and ice, don't use sharp tools.

  • To give the unit extra protection in winter and summer, consider installing a shelter over the unit. Remember that it needs airflow to work properly, so don't smother the machine. There must also be a 2-foot (60cm) clearance above the machine.

  • Make sure to maintain any trees in the vicinity of the heat pump to prevent branches from falling onto and damaging the heat pump.

  • Add insulation to any pipes prone to freezing in cold weather, and educate yourself on how to prevent and thaw frozen pipes safely.

  • Inspect your condenser carefully to make sure that it is undamaged, clear of snow, and that the condensing fan has sufficient airflow.

  • If there is an ice build-up , use a hose or lukewarm water to remove it, rather than boiling water. Boiling water can cause more damage. It is also important not to melt the ice when the temperature is below freezing.

    How to defrost your heat pump

    How to defrost your heat pump

    While heat pumps are super efficient and have been designed to perform well in cold weather conditions, they are prone to frosting up in cold climates with very low temperatures. This requires them to initiate their defrost cycle.

    When this kicks in, you may notice that the temperature drops slightly. This isn't anything to worry about, and the temperature will return to normal shortly.

    Occasionally you'll find that your heat pump is not producing sufficient heat. This can be because it is still defrosting, but it can also mean that the defrosting cycle isn't switching on properly. Keep reading to find out how best to fix this issue.

    Give it time

    It is important to remember that the defrosting process takes time. It is possible that your defrosting system is working and just needs some more time.

    We suggest giving the pump 3-4 hours before making any calls. If your pump isn't working after waiting this long, there may be a bigger problem.

    Further steps if defrosting doesn't occur

    If your pump is still not operating normally after waiting 4+ hours to allow the defrosting system to work, then you'll need to call in a qualified technician.

    We also recommend having a regular service scheduled for your air source heat pump system to ensure it is in the best possible condition.

    More complex solutions for the confident DIY enthusiasts

    If you're in a pinch and unable to get a heat pump technician in to assist you, then there are a few things you can try that might solve the problem. However, this is only recommended if you are fully confident in your troubleshooting skills when it comes to complex equipment.

    It must be noted that if you're unsure what you're doing, you could easily worsen the problem or cause severe damage to your unit.

    So, proceed with immense caution and ensure you've given the air source heat pump at least 4 hours to potentially complete a defrost session.

    Turn on the fan

    Turn on the fan

    If your system has a fan setting, you can try turning the fan on. This can help the heat pump to defrost within 60 minutes. We recommend putting the fan onto the exhaust setting if the outside temperatures are particularly low.

    Unfortunately, this is only a short-term solution, and it is still important to get a technician in to service the machine and make sure that everything is in good working condition.

    Manually start the defrost cycle

    Some air source heat pumps have a manual switch for the defrost cycle. If your heat pump has this setting, you can give it a try. The defrost setting reverses the system, essentially turning the heat pump into an air conditioner for a short period, allowing the ice to melt and the refrigerant to warm up.

    On many machines, this cycle will start automatically. However, if there is a malfunction where the machine is not initiating the defrost cycle by itself, you may be able to activate it manually.

    Change the position of the sensor

    An air source heat pump requires a longer period to defrost in frost conditions. If the sensor (located on the exterior section of the unit) is positioned in a warm spot with sunlight, it could cause the machine to stop the defrost cycle before it has completed the cycle.

    When doing this, it is important to mark the original position of the thermostat so that you can replace it accurately later. This option is a last resort, and it would be better to call in a technician to avoid causing accidental damage to your unit.


    How efficient are air source heat pumps in winter?

    Modern air source heat pumps work very efficiently in winter; many are significantly more efficient than their competitors. Research shows that they can be three times more efficient.

    Can an air source heat pump work with existing radiators?

    Yes, they can! Most existing radiators are compatible with air source heat pumps and won't need to be replaced. All that needs to happen is that a low flow temperature needs to be used. This is usually no issue with bigger radiators, but you'll need to check your small radiators to make sure that a heat pump works with them.

    Find out more about heat pumps

    If you're looking for an alternative heating system to your gas boiler or oil boiler, an air-source heat pump could be a great option.

    At PlumbNation, we specialise in plumbing supplies for a range of heating solutions. For more information, explore our website or get in touch with our team.