Category - Heat Pumps
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Will Scholfield, Engineer

30 Jun : Updated 22 Apr ● 10 min read

Air source heat pumps: Everything you need to know

If you're on a mission to live a more eco-conscious lifestyle, or if you’re simply looking for alternative ways to heat your home, you may have heard of heat pumps. 

Air source heat pumps are just one of the types of heat pump available in the UK. But what are air source heat pumps, and how do they work? 

Whether you're looking to do your bit to help the environment or on the hunt for new methods of heating your home, we'll tell you everything you need to know about air source heat pumps in this guide.

What are air source heat pumps?

Air source heat pumps (ASHP) help transfer heat from outside air into your home. The air is compressed and used to generate more heat which can circulate around your central heating systems.

This low-carbon method comes in two forms: air-to-water and air-to-air.

  • Air-to-water refers to heat being generated to produce hot water for your radiators, showers, underfloor heating and any other appliance that uses water.
  • Air-to-air, on the other hand, refers to heat being directly transferred into the home via a fan or air conditioning system.

Air source pumps also come in types: monobloc and split. A monobloc is a bit like a combi boiler and is literally a ‘single block’ system, where the heat pump has all of its components (apart from the hot water cylinder which is installed in the home) located inside a heat pump unit situated outside the home. A split heat pump unit, however, has both an outside unit, which incorporates the heat exchanger and refrigerant, and an internal unit, which sits inside the property, usually in a utility or boiler room.  

How do air source heat pumps work?

Much like a refrigerator, air source heat pumps use electricity to absorb heat from the air and use it to generate heat for the home, but how does it all actually work?

1. Air blows into the heat pump. Inside the heat pump is a heat exchanger and a refrigerant which helps absorb heat from the air. This heat is warm enough to turn the refrigerant liquid into a gas. This gas is then compressed to increase the temperature.

2. This compressed gas is then transferred over to the cool air/water to make it warm. It will then circulate around your home, heating radiators and providing hot water.

3. Once enough heat has been transferred, the refrigerant will condense back to a cool liquid for the cycle to repeat again.

The pros and cons of air source heat pumps

If you're unsure about whether air source heat pumps are a valuable investment, here are a few advantages and disadvantages for having them help heat your home:

The pros of air source heat pumps

Air source heat pumps are able to provide homeowners several benefits. These include:

1. Environmentally-friendly heating

Since you'll be using outside air to generate heat for your home, air source heat pumps can help reduce your carbon footprint. In comparison to fossil fuels like oil and natural gas (and, in some instances, electrical energy that has been generated through unsustainable means), air is a fully renewable energy source.

2. Help with reducing energy bills

It’s not only your carbon footprint that air source heat pumps can reduce, though, they can also help to bring your home’s energy bills down. As the name suggests, air source heat pumps operate using the outside ambient air temperatures to meet your heating and cooling needs. This means you won’t be reliant on more traditional energy sources, many of which are becoming increasingly expensive. Whilst the upfront costs of getting an air source heat pump will be significantly higher than those of a boiler, it’s possible that it could save you money in the long run.

3. Government funding

In an effort to make homes more sustainable, the UK government has introduced a Boiler Upgrade Scheme. This allows participants to receive £5,000 towards the upfront costs of an air source heat pump. 

Just bear in mind that after applying for a voucher through this scheme, you must redeem it within three months or else it will expire. So, if you receive a voucher through the Boiler Upgrade Scheme at the beginning of May, you will need to have organised for your new air source heat pump to be installed by the beginning of August.

4. Ability to heat and cool your home

Air source heat pumps aren’t just used for heating your home, though, they can also be used to provide much-needed air conditioning during the summer months, too!

With temperatures reaching record-breaking highs in recent years (a trend that shows no signs of slowing), more and more of us are looking to install air conditioning systems in our homes.

Not all air source heat pumps are able to operate as cooling systems, though, so you’ll need to check your make and model carefully in order to be sure that it will be able to provide air conditioning. 

5. No fuel tanks

Since you're using outside air, there is no need for fuel tanks or storage. If you were using biofuels, for instance, you would need to have large stores of organic fuels sitting outside or close to your home in order to keep your central heating system operating properly.

The cons of an air source heat pump:

Despite their environmental benefits, air source heat pumps aren’t always a perfect solution to your home’s heating requirements. Let’s take a look at some of the disadvantages of getting a heat pump installed in your home.

1. Installation can be expensive

Air source heat pumps are considerably more expensive to install than traditional gas or oil boilers. On average, installation costs range from £8000 all the way to £18,000 - a great deal more than the £1000 to £2000 it typically costs to install a boiler.

This means that, for many homeowners, the cost of installing a heat pump is simply unaffordable, even with a government grant.

2. Low heat supply

Compared to oil and gas boilers, air source heat pumps don’t produce as much heat at the same rate. This means that the water running through your home’s radiators or underfloor heating won’t be as hot as if it were produced by a boiler.

In larger homes especially, the reduced heating capabilities of ASHP systems tend to mean that more or larger radiators are required.

3. Good insulation needed

In order to maximise the potential of your air source heat pump, you'll need to ensure your home is well-insulated. If heat can escape easily via windows and doors, you’ll end up using more energy than you need to in order to keep your home warm. This, in turn, will see your energy bills increase beyond what might otherwise be the estimated costs.

4. They lose efficiency in temperatures below 0°C

ASHPs can work at lower temperatures but they will lose efficiency as a result. This means that, if the ambient air temperature falls below freezing, an air source heat pump may struggle to provide enough heat for your home. 

Of course, this is a bigger problem in the winter months when the UK’s weather regularly drops below 0°C and could lead to homeowners relying on ASHPs needing to install additional heating methods to meet their hot water requirements.

5. They can sometimes be a tad noisy

This sound from an air source heat pump is produced by the fan moving air to the heat exchanger. It’s usually only the same volume as a fridge, however, if the fan is working extra hard, it can be noisier.

This issue, however, is something engineers are looking to improve upon in the coming years.

6. UK homes aren't designed for them

UK homes were not built for ASHPs. Since the vast majority of UK homes use a gas boiler, the air source heat pump installation process can be complex to ensure they can be used effectively to heat your home. 

You need to consider the amount of plumbing that will need to be replaced as well as having sufficient space to store your water tank.

Is it worth getting an air source heat pump?

Now you know the what, why and how of air source heat pumps, let’s weigh up whether or not getting one is the right choice for your home. 

Being such a big investment, there are a lot of factors you'll need to consider before installing an ASHP, including:

  • Cost: First and foremost for many of us will be the cost considerations of a new central heating system. Air source heat pumps certainly aren’t cheap, so you must do the maths before deciding to purchase one in order to work out whether it’s going to be worthwhile financially. In the table below, we’ve outlined the average costs of all the elements required for an ASHP heating system.
ItemCost rangeAverage cost
Supply air source heat pump: Air-to-water (5kw - 17kw)£4,000 - £8,000£6,000
Install air source heat pump: Air-to-water£5,000 - £10,000£7,500
Supply and install air-to-air air source heat pump (heating capacity 5kW)£1,600 - £3,100£2,350
Option - upgrade to larger radiators (assume 10 in property)£1,000 - £3,000£2,000
Option - underfloor heating throughout£5,000 - £15,000£10,000
Option - replace all heating system pipework (i.e. microbore to larger diameter)£2,000
Upgraded insulation - cavity wall£500 - £1,000£750
Upgraded insulation in roof (blanket roll)£500 - £1,000£750

Upgraded floor insulation

£1,000 - £5,000£3,000

With the Boiler Upgrade Scheme, however, 90,000 homes in the UK can save around £5,960. 

  • Insulation: You need to make sure your home is well-insulated, otherwise your home might not be able to retain the heat that your air source heat pump generates. Poor insulation can lead to higher energy bills if not addressed.
  • Size: Will your ASHP be able to provide enough heat and hot water for your home given its size? Smaller and more compact spaces will benefit from air source heat pumps much more than larger homes, with the latter typically needing to supplement the hot water generated by a heat pump with additional electric or gas-powered heaters.
  • Space: Air source heat pumps can be quite large pieces of kit, so you’ll need to assess whether you actually have enough outside space to fit the unit. As it’s usually smaller properties that are best suited to ASHPs, this issue becomes all the more acute since they will likely have smaller garden areas and smaller interior rooms, too. 

How can the Boiler Upgrade Scheme help with funding an air source heat pump?

In an effort to reduce carbon in our homes, the Boiler Upgrade Scheme (BUS) provides grants and funding for 90,000 homes in the UK to install environmentally friendly devices. 

Property owners can apply for a £5,000 grant to pay for the installation of an air source heat pump. 

If you’re looking for ways to save and want to reduce the threat of climate change, the BUS is a great service you should definitely consider using. 

Help keep your house warm with BOXT

If you’re looking for ways to make your home heating system more efficient, an air source heat pump working alongside a new boiler is a great investment. 

At BOXT we’re always here to look after our customers’ needs. Check out our boiler replacement services or book a repair and we could be at your home as quickly as the very next day.