Changing the way we heat our homes: air source heat pumps

Our previous post looked at ground source heat pumps as an alternative to gas boilers.
:arrow_forward: Next up: air source heat pumps. :arrow_backward:

Air source heat pumps have become popular with domestic setups in the UK, with 87% of people choosing this kind of heat pump. :open_mouth:

An air source heat pump absorbs heat from the air outside to heat your home. They do this by blowing air over a series of tubes filled with a liquid refrigerant. This liquid absorbs heat from the air and turns into a gas. The pump uses electricity to compress this gas and raise its temperature - warmth which is then transferred into heat or water, depending on which kind of system you opt for. This heat can be used in your home’s radiators, underfloor heating and hot water systems. Like a ground source heat pump, they use electricity to run, but the heat output is greater than the electricity input, so they are energy efficient. If you put 1 kWh of energy in, you’ll get around 4 kWh out.


There are two main types of air source heat pumps: air to water and air to air.

Air to water pumps can heat your home and your hot water through pipes and radiators. They work particularly well with an underfloor heating system. You can see some case studies on the Energy Saving Trust’s website. Air to water pumps are eligible for the government’s Renewable Heat Incentive (RHI) scheme, which can contribute towards the cost of installing them in the first place.

Air to air pumps heat or cool air in your home, but they won’t heat your water as they only work in air conditioning systems. They’re also not eligible for the government’s RHI scheme, which is something to bear in mind when looking into which system works best for you.

To install an air source heat pump at home, you’ll need some outdoor space with good ventilation around it. They can be placed on the wall or on the floor, and they need less space than ground source heat pumps, which might account for their popularity. Installation costs between £6,000 and £18,000. So marginally cheaper than a ground source pump, but still a fair penny. :money_with_wings:

I can see why ground source heat pumps aren’t as popular, because you have to have quite a specific set up (including enough space in your garden) and there can be lots of installation work. Personally, I would sway towards an air to water heat pump. :potable_water:

Now we’ve looked at both, which one seems more appealing to you and why?

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Some great info on what’s likely going to be the future of heating most UK homes!

If I had the space and money, I would go for ground source any day - More efficient and consistent in winter times, and also immune to snow, which air source pumps are not.

Also worth noting that some Air to water heat pumps (namely the mitsubishi ecodan line) can cool your homes, but you’ll need underfloor heating (which would then be underfloor cooling) or special fan assisted radiators like the mitsubishi I-Life2 .

Might also be worth talking about the the CoP (in short, how efficient the pump is) can vary wildly based on outdoor temperature with heat pumps.

It does seem like space and money are the biggest blockers for installing ground source heat pumps @izzyhunt. Hopefully as the years wear on we’ll see both of these shrink. I think many are waiting and watching this space.

I also didn’t know that air source heat pumps couldn’t function in snow. Would be another obstacle the roll out in Britain. Looks as though seasonal performance fluctuates over a year but most domestic ASHPs don’t dip below 2.5 output so would still be putting out 2.5x more than they’re taking in which should be sufficient…

With snow it depends on placement, if its on the floor exposed and we have a foot of snow then oh no, they can be elevated onto walls, but even then they like to suck in the snow and clog the coils, meaning it has to run a defrost cycle. It doesn’t stop them working, just makes them less efficient. Even if the heatpump was totally taken out of action by snow, they would still be able to use the emergency heating elements to heat your home.

That’s interesting and goes some way towards supporting the claim that they can still extract heat when air temperatures are as low as -15°C :thermometer:

How do you find the maintenance of your ASHP @izzyhunt ?