What Size Air Source Heat Pump Do You Need?

heat pumps with an engineer

A 5kW heat pump will suit the average three-bed home

If you have a large house, a 12kW or 16kW model is best

Buying a heat pump could save you £3,900 over the machine’s lifetime


Air source heat pumps can save you thousands of pounds, tonnes of CO2, and reliably keep your home warm for the next two decades.

And they’re on the rise. From April 2022, the government’s Boiler Upgrade Scheme can save you £5,000 on a new air source heat pump – as well as £6,000 on a ground source heat pump.

But you don’t just want any heat pump. You want the best heat pump, the one that will suit your home perfectly, and provide the greatest value for money. We’ve got you covered.

heat pumps with an engineer

How big is an air source heat pump?

Air source heat pumps generally range from 5kW to 16kW. The bigger your home, the higher the number of kilowatts you’ll need.

Typically, a 100m² property with three bedrooms will require a 5kW air source heat pump, while a 200m² home will need a 10kW machine.

A poorly insulated house that’s 250m² or bigger may require a 12kW or even 16kW system.

In terms of physical size, your new air source heat pump will generally stand between 1 and 1.5 metres high, and between 0.5 and 1 metre wide, which is roughly the size of a standard washing machine.

They usually weigh between 60 and 100kg, which is more or less the same as the average UK adult.

grant aerona3 air source heat pump

How big is a ground source heat pump?

A ground source heat pump is usually between 5kW and 16kW, and stands at 1.1m high by 0.6m wide.

However, you can usually opt for a slightly smaller model – a 4kW model instead of a 5kW model for a 100m² home, for instance – because ground source heat pumps reliably provide a constant level of heat, whatever the season.

When the air temperature drops in winter, air source heat pumps require more electricity to provide the same amount of warmth.

Ground source heat pumps have no such problems, as the ground stays between 10°C and 13°C throughout the year, meaning they don’t need to have that extra capacity.

The heat pump itself isn’t particularly large – at 1.1m by 0.6m, it’s the height and width of the average six-year-old child – but the area you’ll need for the attached pipes may be.

If you opt for a horizontal system, it’ll be cheaper, but it’ll require around 700m² – 7m by 100m – of space for pipes to be laid about a metre under the ground.

You can use a vertical system, in which one or two boreholes between 90m and 160m deep are drilled into your garden, but this is considerably more expensive than the horizontal option.

How to work out what size heat pump you need

If you have a new-build property, just follow the handy table below to get the perfect size of heat pump for your home.

House sizeNumber of bedroomsAir source heat pump sizeGround source heat pump size
100m²35kW4kW
200m²410kW9kW
300m²5-616kW15kW

If your home isn’t completely new, you should get a heat pump company to provide you with a free heat loss assessment before they give you a quote for one of their products.

They’ll perform a calculation based on the age of the property, its size, the number and size of its rooms and radiators, and whether it has single or double glazing.

The company will also check your insulation level and whether you’ve installed underfloor heating pipes.

If you have poor insulation and/or no underfloor system, you can still use a heat pump to warm your home – it’ll just need to be bigger to make up for these shortfalls.

How can you prepare your home for a heat pump?

If you want to cut your heating bills and turn your home into one that only needs a small, cheap heat pump, there are a few ways to save:

  • Loft insulation
  • Wall insulation
  • Double glazing
  • Underfloor heating, if possible
  • Draught-proof your doors
  • Make sure you have room outside
  • Clear a 1m by 1m space for a hot water cylinder inside

Pros and cons of a large heat pump

ProsCons
Can reliably heat your home in almost any weatherMore expensive than a smaller model
More efficientHigher energy bills
Offers more protection against blackoutsRequires more space
You can use all the electricity your solar panels generate
More eco-friendly

The best large heat pump on the market

The Grant Aerona³ R32 is the best large heat pump around, hands-down.

This 17kW air source model will comfortably heat practically any house with an incredible efficiency rating of 479% – meaning it’ll create 4.79 units of heat for every unit of electricity it absorbs.

At 120kg, it’s below average weight for its power, and you can even get a seven-year guarantee if it’s installed by one of Grant’s approved G1 tradespeople – though considering it works at temperatures as low as -20°C, it probably won’t let you down anyway.

The Aerona³ R32 can be picked up for an extremely reasonable £5,400, plus installation.

The best small heat pump on the market

The 5kW edition of the Samsung R32 Monobloc air source heat pump is your best bet if you’re looking to heat a house of around 100m².

For a relatively low initial price of £3,500, you can get an efficiency rating of 485% – that is, 4.85 units of heat for every unit of electricity. Now that’s efficient.

Its sound level is just 45dB, which is equivalent to light rain, and it’s a small unit, weighing in at a svelte 58.5kg.

And its slight frame belies its durability, as it’s able to keep working even if the mercury drops to -25°C. It also comes with a seven-year warranty when set up by an approved installer.

Next steps

You’re now ready to begin saving money and energy with a new heat pump.

All you need to do is ask for a free heat loss assessment for your home, make any necessary improvements, and then purchase the perfect heat pump for you.

And what’s more, with the government’s Boiler Upgrade Scheme (starting April 2022), you could save £3,900 over the machine’s lifetime – and reduce your emissions by more than two tonnes of CO2 per year. That’s one-third of your carbon footprint, gone.

Josh Jackman Senior Writer

Josh has written about eco-friendly home improvements and climate change for the past three years. His work has featured on the front page of the Financial Times; he’s been interviewed by BBC Radio; and he was the resident expert in BT’s smart home tech initiative.

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