Installing an air source heat pump – what’s involved

03 October 2023 | OVO Energy

If you’re thinking about getting an air source heat pump (ASHP) installed, that’s great news. You’re taking a vital step towards helping bring down the nation’s carbon emissions.

It’s quite common for people to be put off changing their heating system because the process seems daunting. We’ve put this guide together so you’ll know exactly what to expect before, during and after the installation of your low-carbon heating system. 

Keep reading to learn how to find a qualified engineer, how to keep things working smoothly once installed, and how to apply for the £7,500 government’s grant scheme, the Boiler Upgrade Scheme (or BUS).

Should I buy an air source heat pump?

At the moment, around 14% of the UK’s carbon emissions come from home heating. If we’re to meet the government’s net zero emissions target by 2050, we’ll need to cut our home heating emissions to zero.

Reasons to join the heat pump revolution:

  • Reduce your carbon footprint and help fight climate change
  • Potentially reduce your heating bills
  • ASHPs are low maintenance
  • Save money off your install through the Boiler Upgrade Scheme (BUS)
  • You could also be increasing the value of your home

It’s worth noting that unless your home is well-insulated, the heat pump won’t work as efficiently and could end up costing you more to run. So if you don’t already have insulation in your loft and cavity wall (if your home has a cavity) and double-glazing, it would be a good idea to look at these first. 

Check to see if you’re eligible for energy efficiency and insulation grants

Man kneeling down fitting a heat pump in the garden

What size air source heat pump do I need for my home?

It’s important to get the size (or more accurately, the power or capacity) of your ASHP right. Don't worry though, your engineer will be able to recommend the correct-sized heat pump for your home and heating system after they’ve carried out a thorough survey.

Air source heat pump sizes for the average home range from 6kW to 8kW. As you’d expect, bigger homes need more powerful heat pumps. And less powerful heat pumps are needed for well-insulated homes, as they don’t need to generate as much heat as less heat will escape.

How you distribute the heat in your home is also a factor. ASHPs work best with low-temperature heat emitters, like underfloor heating systems. If you’re using radiators, they might need to be bigger than the ones you use for gas or oil central heating. 

How to find the right air source heat pump installer

If you want to be eligible for the Boiler Upgrade Scheme (BUS) and get £7,500 off your install, make sure you use an installer who’s certified under the Microgeneration Certification Scheme (MCS). This means the installer has completed installer training and must follow certain codes of conduct and industry compliance. Not all heat pump installers have this certification, so make sure you do your homework.

Our friends at Heat Geek have a nationwide network of award-winning installers – which is one of the reasons we’re partnering with them to test out our new heat pump offering. Register your interest and we’ll let you know when we're installing in your area. 

Can I install an air source heat pump myself?

In short, no. Installing an air source heat pump is definitely not a DIY job. Heat pumps need to be set up correctly to run efficiently, they need optimising for each home otherwise you could end up with unnecessarily high bills. Plus, if you did do the work yourself – unless you’re MCS certified –  you couldn’t apply for any form of government grant like the Boiler Upgrade Scheme.

MCS certified engineers have knowledge in all these areas:

  • Low-temperature heating systems
  • Vapour compression cycle principles
  • Weather compensation controls 
  • Behaviour characteristics of the heat pump controls
  • Operating conditions of the heat pump
  • Electrical connections and plumbing circuits and how to control and optimise them

If you’re keen on getting involved, speak with your installer and they might be able to guide you in some stages of the job. For example, parts of the pipework and its insulation could be worked on by a good DIY-er. But don’t attempt any work on the system without guidance from a fully qualified engineer.

How much will it cost to install an air source heat pump?

The cost of an air source heat pump installation depends on a number of factors, including:

  • The model of ASHP you choose
  • How well-insulated your home is
  • The size of the ASHP you need (more powerful ones are more expensive)
  • How complex the installation will be (you might need underfloor heating or new radiators, for example)

As a rough guide, the Energy Saving Trust reckons that installing an ASHP system will typically cost around £14,000. That might vary, depending on the size of your home and your requirements. So the best way forward is to get some quotes from registered installers. 

To find out more about the costs of an ASHP, including the savings you can make, check out our comprehensive guide on how much does an air source heat pump cost. 

You could be eligible for the Boiler Upgrade Scheme. Read on below for more information.

Step-by-step guide to air source heat pump installation

What will happen before installation?

Before any installation, an engineer will have to complete a thorough survey of your home. This is to make sure they recommend the right ASHP for your property. They’ll carry out a full assessment, then give you a written report of their recommendations. 

It’s also mandatory for them to give you an estimate of how much it will cost to run your heat pump – and how much you could save. This is not a guarantee, but for guidance only. 

This is the time to ask any questions you might have about the installation itself, and if you need to prepare anything inside or outside your home.

How long does it take to install an air source heat pump?

The amount of time it takes to install an ASHP varies for each home, depending on size and complexity. Remember, it’s not just a case of installing the pump itself, but all the inside elements too. 

For a fairly simple install in a mid-sized 3-bed house, you can expect 3 engineers to be on site for around 4 to 5 working days. Of those days, you might be without hot water for 1 or 2 days. 

Your installer should be able to give you an accurate estimate of time after they’ve done the initial assessment.

What will happen during the installation?

The installation process can take a few days, as there are many elements to consider. Here’s a summary of what you can expect:

  1. The ASHP unit itself needs to be installed outside, on a flat concrete base. There’ll be no need for digging, like there would be with a ground source heat pump installation. The installer will make sure there’s good airflow and that it’s not too close to your neighbours. 
  2. The installer will also connect the return and flow heating pipes and electrical power cables outside your home. Once this is complete, your installer will move inside. 
  3. Most heat pumps need to have a new hot water tank installed inside the home. 
  4. In most cases, a few or more of your radiators will have to be replaced. The main exception would be if a house already has a heat pump installed. So your installer will replace your radiators and connect your new ASHP. Or, if you’re using an underfloor heating system, the installer will need to either set that up or connect the ASHP to your existing system. 
  5. All the controls and thermostats will need to be installed inside your home. 
  6. The installer will tidy up and approach you to explain how the system works. They’ll also start it up to make sure it’s working to the manufacturer’s standards. 

As you can see, having an ASHP installed is not a minor job. But how disruptive it is depends on your current system. If you have fairly recent pipework that can be used to fit the new emitters, it could take just 2 to 3 days, with minor disruption. 

If your pipework and radiators need replacing, though, that means work in every room, lifting carpets and floorboards. 

Whatever kind of system you have, it’ll need to be disconnected while the new one is fully installed. This means you’ll be without heating and hot water for at least a day. 

What do I need to know after my air source heat pump has been installed?

Once your ASHP has been installed, your engineer will start up the system and talk you through how it all works. They’ll explain all the ASHP functions and show you how to change settings where needed. They might also offer you a maintenance package and aftercare support 

As most ASHPs are weather compensated, they can keep a steady temperature indoors no matter what the weather’s doing outside. When the weather turns colder, your ASHP will work harder to keep your home temperature just the way you like it. This is all done automatically, without you having to do a thing – which is why some call ASHPs a “fit and forget” technology. Happy days! 

How much maintenance does an air source heat pump need?

Thankfully, ASHPs don’t need much maintenance at all. You might need to occasionally take a look at the outdoor fan unit, to make sure it’s free of debris. It’s also worth checking on the pipework’s insulation every now and then, to make sure there’s no sign of a leak. Just book an annual service to maintain the manufacturer's warranty and that should be enough to keep your ASHP ticking along.  

What does an installed air source heat pump look like?

OVO engineer showing an older couple how to use their heat pump in the garden

The ASHP fan unit itself sits against an outside wall (or on a flat roof) of your home – they measure around 120cm high, 100cm wide and 40cm deep. So about the same size as a washing machine, but thinner. This will connect to 1 or 2 hot water cylinders inside – the cylinders measure around 60cm wide by 160cm high. 

You might also need a buffer tank, which is about a third of the size of the hot water cylinder (some cylinders combine both hot water and buffer in one). The ASHP control box will also be inside your home. This measures about 40cm x 40cm x 10cm. 

In some rarer cases there’ll also be some circulation pumps and pipework, as well as any additional controls for underfloor heating. It’s ideal if this can all be placed in a ‘plant room’ – which could be a utility room, garage or airing cupboard. This makes it simple for the engineer to access all the components during maintenance work or repairs. 

How to benefit from the Boiler Upgrade Scheme

The Boiler Upgrade Scheme (BUS) is a government-funded scheme to encourage homeowners to install renewable heating technology and lower their carbon emissions. It’s been designed to help our nation reach that all-important net zero 2050 target. These grants will make £7,500 available up front, to support those installing an air source heat pump.

Find out if you're eligible for the Boiler Upgrade Scheme

Want to be a heat pump pioneer?

We're bringing you something exciting. We’re inviting customers to test out a special heat pump offer. To find out more, register your interest and we’ll let you know when we're installing in your area.

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And if you have any more queries about air source heat pumps, why not head to the OVO Forum? The Forum is where our community comes together to share their firsthand experiences of living with tech. There are tonnes of discussions about every aspect of heat pumps, so why not get involved and join the conversation?