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Installing an Air Source Heat Pump: What to Expect

installing an air source heat pump on the exterior of a house
(Image credit: Daikin)

Installing an air source heat pump isn’t something you’ll be able to undertake yourself, but it’s in your interest to understand the process when thinking about a switch to this renewable heating source. 

Finding the right professional to commission your air source heat pump will put your home's heating in good hands, and once the installation is complete, there's little you'll need to do apart from learn how to use your new system. 

This guide breaks down what you can expect when installing an air source heat pump, so you can make sure you're informed every step of the process. 

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Finding an Installer

Why a Professional Should Be Installing an Air Source Heat Pump

Installing an air source heat pump (ASHP) requires a fundamental understanding of low temperature heating systems, vapour compression cycle principles, weather compensation controls and the behaviour characteristics of the heat pump controls is required to specify the system correctly and commission the operating conditions of the heat pump.

Air source heat pumps have a refrigerant vapour compression cycle and run at low temperatures to optimise efficiency. There are a number of contributing factors that can influence the efficiency and ASHPs are not devices that simply turn on and off like traditional boilers. 

All of the working settings must be set up or the technology may not achieve the desired results or alternatively could use a lot more electricity. 

Air source heat pump systems will have electrical connections that need to be made by suitably qualified electricians as well as plumbing circuits that need to be made by unvented system qualified and experienced installers. Given the low flow temperatures associated with ASHP systems the emitters also need to be specifically sized and controlled to optimise the system.

Can I Install an Air Source Heat Pump Myself?

Installing an air source heat pump is not a DIY activity. Once the system has been designed then there could be some elements of the pipework that could be installed by a competent DIYer. The insulation on the pipe could also be applied by a DIY person but make sure you get full guidance from a qualified engineer before attempting any of the installation yourself. 

installing an air source heat pump in a garden

Air source heat pump manufacturer Daikin operates a Certified Installer scheme.  (Image credit: Daikin)

How to Find a Reputable Air Source Heat Pump Installer

An air source heat pump should be installed by an accredited Microgeneration Certification scheme (MCS) installer because they will have completed installer training and also have to comply with certain codes of conduct and industry compliance in order to certify the installation.

The best way to find a good installer is by word of mouth. If you know anyone who has had one installed then ask them for a referral. You can also check the MCS website for registered installers near you or alternatively get a referral from a manufacturer or check their website for approved or accredited installers that cover your area.

The best route to market for air source heat pump installations is to get a supply and install contract. That way the chain of custody is complete and there is full continuity from specification right through to commissioning. It is possible to purchase the system components separately but you would need to be sure that they are all compatible with each other. 

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When Should I Look for an Air Source Heat Pump Installer?

The earlier in the process that you can appoint an air source heat pump installer the better. There are lots of components that need to be installed and there are also other trades that need to also have their products installed to do it. 

It is important to be sure that all the equipment can fit in the plant room and that the distribution pipework and wiring routes do not clash with other services or structural elements.

Specifying an ASHP

Choosing the Right Type of Air Source Heat Pump

There are two main types of air source heat pump:

  • Monobloc systems have all the refrigeration components sealed in one unit. Therefore no refrigerant connections need to be made on site so the system can be fully installed by a plumber and electrician. The monobloc unit should ideally be less than 10 meters from the hot water cylinder or underfloor heating manifolds.
  • If you need the outdoor unit to be further from your property or you live in a very cold climate then a split type heat pump could be more appropriate. A split ASHP has half of the heat pump (with the actual fan in it) outside and half of it inside and the two halves are connected together with refrigerant pipes on site. 

What Size Air Source Heat Pump Do I Need for My Home?

The size of the air source heat pump that you require for your home will be determined by the installation design engineer. 

The heat loss and hot water requirements of the property is calculated, which takes into account the local weather conditions as well as the design temperature requirements of the home, and the heat pump is then specified to cover the load.

a monobloc air source heat pump

(Image credit: Vaillant)

Will an Air Source Heat Pump Supply Heating and Hot Water? 

The air source heat pump will be able to supply space heating and domestic hot water to the home. 

The domestic hot water is stored in a specific heat pump cylinder, which is similar to a standard hot water cylinder but has a bigger heat exchange coil. The cylinder capacity is also usually larger than for a boiler because the stored water temperature is a bit lower to optimise the efficiency of the heat pump. 

Installation

What Will an Air Source Heat Pump Installer Do?

The installer will design and specify the equipment including the heating capacity, location of equipment, distribution networks and the user interfaces such as room thermostats.

They will also physically install the system and let you know what is not included in the installation (especially in an existing property where things like repairing decoration work is not usually included). 

Some installers are also fully qualified plumbers and may include other sanitary and plumbing installation works within the contract. 

The installer will also commission the air source heat pump system and give the homeowner a handover and explain how it all works. They may also offer a maintenance package and aftercare support.

What Does an Installed Air Source Heat Pump Look Like?

An air source heat pump unit is sited outside the house and you need a controller and possibly two cylinders inside. The fan unit, which is often around 1200mm tall, 1000mm wide and around 400mm deep, will be connected to at least one hot water cylinder which is around 600mm wide by around 1600mm tall. 

There could also be a further cylinder (buffer tank or low loss header) around a third of the size of the hot water cylinder. Indoors, there will be an ASHP control box which is around 400mm x 400mm x 100mm deep.

There will also be a number of circulation pumps and pipework, as well as a manifold and control box for any underfloor heating

This is all best placed in a plant room that allows enough space for the materials and pipework but also for any engineer to perform any future repairs or maintenance. By putting it all together it is easier for the engineer to see all the components in one place and also understand the circuits and controls.

An air source heat pump installed outside of a home

(Image credit: Panasonic Heating & Cooling Solutions)

How Long Does it Take to Install an Air Source Heat Pump? 

Depending on the complexity of the works, an air source heat pump could be installed in as little as a day. 

Usually the preparation work such as building a solid base for the outdoor unit to stand on would need to be in place before the installation date. 

How Much Will it Cost to Install an Air Source Heat Pump?

The cost of installing an air source heat pump in a new or self build to be upwards from £11,000. The cost will be significantly higher in an existing property, taking improvements to the house’s fabric and replacing and removing existing heating systems into account. 

(MORE: Air Source Heat Pump Costs Explained)  

Post-installation

What do I Need to Know After my Air Source Heat Pump has been Installed?

Once your air source heat pump has been installed you should not need to do much as the system should be commissioned by the installer. 

The installer should hand over the system to you and explain how it works and only allow you to change settings that you are fully competent to do. 

How Much Maintenance Does an Air Source Heat Pump Need?

Most of the time the maintenance on air source heat pump systems is visual. There will be inspections that you can do such as checking the outdoor unit has free air movement and is not blocked up with leaves or other debris.

Also check the insulation on all pipework is intact and that there are no visible signs of leaks or corrosion on the pipework or casing.

You will however need an annual service on your central heating system that may also be directly connected to the ASHP. 

Any non-visual maintenance will most likely need to be carried out by a suitably qualified and experienced engineer.

David is an expert in sustainable building and energy efficiency and is also director of Heat and Energy Ltd.