What Is an Air Source Heat Pump and does it work during the winter? Pros and Cons

If you’re researching systems to heat your house, you might have stumbled on air-source heat pumps. They cost less and can run for long periods. So, you might find yourself wondering, how do air-source heat pumps work?

While gas heating has served us for long decades, it’s about time till we replace it entirely with a cleaner alternative.


One possible candidate for the home heating systems is the air source heat pump or the ASHP. This is an alternative to heat pumps that use thermal energy (from under the ground).

An air-source heat pump is a device that uses ambient heat to warm up your house. Unlike most other heating systems that burn fuel, an air-source pump doesn’t produce heat per se.

The way it works, it absorbs heat from the air outside the house and transfers it to water. You can then use this water to heat the house or take a hot shower.

Not only can an air-source heat pump keep you warm during winter, but it can also keep you cool during summer. The device can control the amount of heat in the house. It’s usually installed outside the house, where there’s ample space and a direct line to ambient heat.

How Does an Air Source Heat Pump Work (during winter)?

An air-source heat pump (ASHP) has a main external unit that goes outside your home with piping that extends all over your house.

Instead of generating heat by combustion reactions, it simply transfers the energy from one place to others.

It works in two modes: summer operation and winter operation. One releases heat into your home while the other absorbs it.

To get a grasp of how air source heat pumps work during the winter, you need to imagine a reverse fridge.

Let’s take a closer look:

Heat Absorption from Latent Air

The external pump takes up heat from the air outside. Yes, even cool wind has some latent heat!

To speed things up, a fan circulates the air over the pump. This energy is then transferred to a liquid coolant.

This coolant has a relatively low boiling point, so it evaporates quickly to proceed to the next step.

Once you install and plug in your air-source heat pump, the fan will start running. This fan acts as a sort of funnel. It sucks the air into the main body of the air-source heat pump.

The air from the outside starts moving around and filling the main chamber. Inside the main chamber of the device, there is a network of tubes. These tubes are full of refrigerant, which is similar to the liquid that keeps your fridge cool. One of the properties of refrigerants is being able to transfer heat from one place to another.

Absorbing the Heat From the Air

After the air-source heat pump fills with air, it can start converting it into usable heat. The next step is absorbing all the heat from the air. As the air moves across the network of tubes in the main chamber, heat transfer occurs.

Usually, the air coming from the outside will be warmer than the refrigerant in the metal tubes.

So, as the air moves, some of its heat will transfer through the metal tubes to the refrigerant.

This causes a phase shift in the refrigerant, turning it from a liquid into a gas. This conversion is crucial for the operation of the pump. Once the refrigerant turns into a gas, you can use it to heat the rest of the house.

Vapor Compression

Moving on, the next step in heating your home is gas compression. The refrigerant gas moves from the main chamber straight into an air compressor. This compressor will increase the pressure of the gas.

This way, you can increase its pressure and temperature while making it easier to transport in small pipes. Increasing the gas pressure has more than one benefit. The second one is that at a higher pressure, the gas will be able to move for longer distances. This can be necessary if you have a large house.

Another benefit is extra heat. When you compress any fluid, liquid, or gas, you’re applying a force on it. Some of the energy of that force can transfer into heat energy. This energy can also go into warming up your house.

The only major issue with increasing the pressure of a fluid is storage. It’s difficult to store a liquid at high pressure, and it can also be quite expensive. Luckily, your air-source heat pump will use the gas straight away and not store it.

By the end of this step, the hot vapor should be flowing into the heating pipes in your walls.

Heat Exchange 

To supply hot water, the vapor goes through a heat exchanger that’s in your water-heating system.

The way this works is that the cold water is exposed to the hot pipes where the vapors flow. Since the pipes are good conductors of heat, the water comes out warm while the vapor cools down.

Generally, most heat exchangers will use water, or some sort of liquid, to transfer heat. There is a tank filled with a liquid that can absorb heat. What happens is that the hot, pressurized gas will move around the tank and start warming it up.

As this happens, the liquid will heat up, and the gas will cool down. Eventually, the gas will cool down enough to start turning back into a liquid. Once all the gas turns into a liquid, it’s collected and sent back to the main chamber. Then you can repeat this cycle as many times as you need.

Using the heat

Once the vapor’s heat is exhausted in heating systems all over the house, it’s channeled to a condenser.

Functionally, the condenser does more or less the opposite of what the compressor does. By reducing the pressure and temperature, it turns the vapor back to the liquid coolant form.

At the end of the cycle, you should have a liquid refrigerant and a hot tank of water. How hot the water is will depend on the size of the tank. It can also depend on how much refrigerant you use.

By then, the process is ready to be repeated all over again. This process can take quite a while. It’s not as simple as turning on a switch and having warm water. So, you need to turn it on in advance before you start using the air-source heat pump.

Keep in mind that all these processes are happening simultaneously, though!

Are Air Source Heat Pumps Efficient? Pros and cons

On a typical ASHP winter operation, you get heat energy that’s threefolds your electricity consumption. That’s 300% efficiency, right there!

This is considerably more efficient when compared to fuel-powered heaters that work on combustion. For instance, a high-efficiency gas furnace comes short at 95%.

Besides saving on your electric bill, you’ll also be helping the environment by making the switch to an ASHP.

Since no burning takes place inside the pump, it produces no carbon emissions, making it a low-carbon heating system.

However, we still can’t call it a zero-carbon process unless you’re using a clean energy source to power the pump. Heat pumps require a lot of electricity and this is a big drawback of this system.

How to Make the Most Out of Your Air Source Heat Pump

While it’s already pretty efficient, you might want to give your air source pump a boost.

Here are some tips and tricks that can help boost the heat exchange process:

Insulate Your Home

There’s only so much the air source heating pump can do for your home if you don’t have the proper infrastructure.

The more cold air is getting inside, the harder it is for the heat exchange to show you a significant difference.

Consider the Noise

While ASHP is efficient energy-wise, nothing’s perfect. The external unit is usually pretty noisy.

So, when you’re planning for the installation, make sure you pick a spot where the sound will affect you the least.

The technology is still evolving though so we can expect that it will improve in the coming years as there are still some challenges.

Don’t Neglect the Maintenance

With proper maintenance, your air source heat pump can keep going for a whopping 30 years before serious issues pop up.

This longevity adds to its energy-efficient character. So, put in a little effort to make sure that the pump is in tip-top shape.

Here are some of the most important routine check-ups to consider:

  • Dusting the foils, fans, and filters
  • Clearing the system supply of any blockages
  • Do airflow intensity check-ups
  • Lubricate the electric engine and all moving parts periodically
  • Replace worn-out belts
  • Check the insulation of electrical cords

Which Type of Air Source Heat Pumps Works Best?

Air source heat pumps come in two main types depending on where and how they release their heat: air-to-water and air-to-air.

Before you commit to one of those, let’s take a quick look at both types:


Air-to-water heat pumps are hybrid systems that pull heat from the outside air and pass it into the wet central heating system.

The main perks of this type are that it works on your radiators, underfloor heating, and water faucets.

On the other hand, it takes invasive (and expensive) pipping to install the system.

Even if you already have piping from an old fuel system, you might have to replace it. That’s because the temperature exchange is different here.

With ASHP, you need pipes with a larger surface area since you’ll be working at a lower average temperature.


The air-to-air heat pump releases the heat to your home through fans and vents.

They’re also referred to as air condition systems that are entirely separated from the wet central heating system.

In other words, it won’t provide you with hot water. You’ll have to get a standalone immersion heater for that.

However, you can still use the pump for both winter and summer operations. As a plus, the installment process is usually much easier than the air-to-water counterpart.

There is also geothermal energy that gets heat from under the ground. This option has become very popular in the past few years.

Pros and Cons of Using an Air Source Heat Pump

As with any device, the air-source heat pump comes with its own set of pros and cons. So, let’s take a look at what some of them could be.


-Low carbon usage, since the device doesn’t burn any fuel

-Uses much less energy than standard heating systems

-Operating this device comes at a lower cost

-You can use the device for heating and cooling

-The device is easy to install and maintain

-You don’t need to buy or store any extra fuel for emergencies


-The device can’t reach the same temperatures as boilers

-You may need to install additional pipes to transfer the heat everywhere

-Some models of the air-source heat pump are noisy

-Your home has to be fully insulated for the pump to work efficiently

Final Thoughts

So, what is an air source heat pump?

The ASHP is a clean alternative to gas heating with a low carbon footprint and high efficiency.

It works by transferring the heat either from or into your home, depending on the season and mode of operation.

All in all, although it requires wet central heating system modifications, it could be well worth the switch!

Geothermal heat pumps are often used as well. A hole is drilled and heat from the earth is used. This works great but can be harder to install. This is why some communities work together and connect their heating systems. We will have to see how these technologies evolve in the coming years.