What size air source heat pump does my home need?

27 May 2024 | OVO

Air source heat pumps are the greener alternative to traditional gas boilers. They can help reduce your energy bills, and, with government grants of up to £7,500 available, now could be a great time to invest. Looking into air source heat pumps? Here’s how to get the right size for your home.

Why does heat pump size matter?

Bigger isn’t always best when it comes to air source heat pumps. It’s really important to find the right size.

  • A heat pump that’s too big and powerful for your home will frequently switch off and on. This can rack up high energy bills and the strain can eventually lead to faults.
  • A heat pump that’s not powerful enough on the other hand won’t be as efficient. It’ll need to run for longer and even then it might not be able to heat your home to a comfortable temperature. This could also lead to higher energy bills.

That’s why you need to find a good MCS-accredited heat pump installer. They’ll meet with you at the consultation stage and recommend a size that suits your home.

How to calculate the right size air source heat pump

All air source heat pumps are rated by the kilowatts (kW) they produce. For example, a 10 kW rating on a heat pump will deliver 10 kW of heat (based on outside air temperature). But most range between 3.5 kW to 15 kW, and are suitable for most homes.

When it comes to finding the right size, there’s no complicated maths for you to do. An accredited heat pump installer will do all the hard work for you. They’ll take the following factors into account, then recommend the heat pump size for your home.

OVO customers and engineer stood in garden with heat pump and phone

What will impact the size of heat pump you need?

Size of your home

Although larger properties tend to need a bigger air source heat pump, it’s not that simple. Your installer will consider the layout of your home, and room size too. That’s because open-plan homes won’t have the same heating needs as those with enclosed rooms.

How well insulated is your home?

Heat pumps work differently to gas boilers. Rather than heating up your water and then switching off, they keep it at a lower temperature constantly. Heat loss can make this process harder, and your heat pump less efficient. But good home insulation can solve this.

Newer, better insulated homes often suit smaller heat pumps that cost less to buy and run. The same can be true of older homes too. In fact, almost all homes suit heat pumps. It’s just that to be as cost-efficient as possible, you might need to improve your insulation.

Right now, the government is offering grants of up to £7,500 off heat pump installations through the Boiler Upgrade Scheme.

Do you have radiators or underfloor heating?

Ideally, air source heat pumps need a larger surface area to efficiently heat your home. That’s why underfloor heating and larger radiators work well with them.

But don’t worry if you have a more traditional heating system. You can always think about adding more radiators or upgrading your existing ones to a larger design. A good heat pump installer will design the right heating system for your home. If they need to upgrade your radiators, they can do this during the installation stage.

What size hot water cylinder do you need?

It’s really important to get a hot water cylinder big enough to meet your home’s demands. If you’re getting an air source heat pump, you’ll need an unvented indirect hot water cylinder. It heats your water via a coil inside which is heated by the air source heat pump.

Generally speaking, a 4-person home needs around 200 litres of water daily. That said, you won’t necessarily need a 200-litre capacity cylinder because some systems partially reheat water throughout the day. The best thing to do is ask your accredited air source heat pump installer for advice.

Interested in saying goodbye to gas? Get your heat pump through OVO.

If you get a heat pump through OVO, it’ll be installed with Heat Geek, and their award-winning engineers. They’ll carry out a full design consultation, and give you a breakdown of the best heat pumps and cylinders for your home.

Not only can your heat pump save you up to £210 a year on your heating bills compared to a gas boiler.1 You’ll also unlock our free add-on, Heat Pump Plus. It gives you a cheaper electricity rate, so you can power your heat pump for less.

Find out more and register your interest

Sources and references

1 Savings of £210 are based on the following comparison: a gas boiler running at 90% efficiency (as per the national average for A-rated boilers) with an annual consumption of 11,500 kWh at 5.75p/kWh, and 77% of consumption used for heating and hot water, versus an air source heat pump with a Seasonal Coefficient of Performance (or efficiency rating) of 4 and an annual consumption of 1,992 kWh at 15p/kWh with the Heat Pump Plus add-on. Rates correct as of May 2024.