What’s Involved in Retrofitting an Air Source Heat Pump in Your Home?

Gas central heating is still the most widely used method of heating homes in the UK. However, with successive governments focused on encouraging energy-efficient heating systems and eventually banning gas boilers altogether, it makes sense to consider a heat pump installation. 

Decarbonising homes is one of the biggest challenges facing the UK as there are literally millions of houses that need to be retrofitted with low-carbon technologies. 

Gas boilers and other fossil fuels seriously affect the UK’s ability to reach its net zero emissions target by 2050 which is why the UK government introduced the Boiler Upgrade Scheme. The scheme provides valuable funding for homeowners to help replace their gas boilers with heat pumps. Demand for efficient heating systems is growing as homeowners become more aware of the threat of climate change and look for more effective and sustainable ways of keeping warm.

Heat pumps can be a great, low-carbon alternative to traditional gas boilers but unless you get one installed in the construction phase of a new-build you will need to look at retrofitting one. Heat pumps can be retrofitted in most buildings, even old buildings, especially air source heat pumps which tend to be less expensive and easier to install than other alternatives.

In this blog we will look at how air source heat pumps (ASHPs) can be fitted into existing homes. The process of retrofitting a gas boiler with an air source heat pump (ASHP) involves several steps.

1.    Find an experienced and reliable heat pump engineer to assess your home

Not all homes are suitable for an air source heat pump (ASHP), so a thorough site survey is essential. To ensure a successful heat pump installation it is essential to commission a heating expert. They will evaluate your home’s heating needs and energy usage. To do this they will carry out a comprehensive inspection of your home and detailed heat loss calculations to make sure the proposed heating system meets the specific demands of your home. The Renewable Energy Hub provides a database of certified heat pump installers across the country which you can access here. 

Heat pump installers must ensure that there are enough energy efficiency measures in place and that the system is accurately designed. Many homeowners may not be aware of the measures that may need to be put in place before their home is ready for a heat pump. The retrofit process is based on a ‘fabric first’ approach which prioritises the thermal performance of the building’s envelope, the walls, floors, roof and doors. Adequate insulation reduces the energy needed to heat your home as well as reducing its carbon footprint. Fitting energy-efficient windows and doors may be considered.

Double or triple glazing and well-sealed doors can prevent drafts and improve energy efficiency. Your installer may suggest replacing your double radiators with triple ones, if they consider your existing ones will not meet your needs. You may also want to think about implementing smart controls. Smart meters for heating systems can use AI to learn when to switch the heating on and give you greater control of their usage. Your heat pump installer will discuss all the options with you including discussing whether you might want to consider installing a solar panel system which can help to provide the electricity required to run your heat pump. 

2.    Obtain quotes from certified installers for installing the heat pump

The cost of installing an ASHP into an existing radiator system will vary depending on several factors such as how big your house is, whether you need to upgrade your radiators, whether you need to install or replace your hot water cylinder, any insulation improvements that are required, whether you want your domestic hot water on a separate system and the brand of heat pump you choose to install. Generally speaking, to supply and install an air source heat pump for a three-to-four-bedroom family home costs will range from £10,000 to £15,000. However, there are many great savings available currently.

There is no VAT to pay until 2027 as heat pumps are classified as low-carbon technology and the Boiler Upgrade Scheme offers grants of £7,500 for an air source heat pump (ASHP). Low-income households can also benefit from grants through the ECO4 government scheme.

To qualify for these schemes the heat pump installation must be carried out by an MCS certified heating engineer. It’s always worth checking what grants and interest free loans might be available in your area. If you need to install new insulation, draft proofing and new radiators the extra costs incurred might make it prohibitive for you to proceed with the installation of the heat pump. It may still be worth going ahead if you intend to stay in your home for a number of years as you will be able to benefit from energy savings over time.

There is also some value in proceeding with the installation if you plan to sell your home, as research by estate agent, Knight Frank has shown that properties that move from an EPC rating of F or G to a C could increase the price of your home by up to 19.6%.

It’s a good idea to approach at least 3 or 4 heat pump installers to compare quotes and decide on the most cost-effective solution for you. We can help with this process by connecting you with vetted professionals. Your air source heat (ASHP) pump quote should include the system’s details, costs and energy output warranties. If you decide to make your own enquiries, watch out for unrealistic promises, hidden fees, lack of transparency, questionable credentials and unproven technologies.

Before you make the decision to install an air source heat pump (ASHP) it’s important to carefully consider the potential energy savings and payback period. 

3.    Obtain permits if required

You do not normally need to obtain planning permission to install an air source heat pump (ASHP) as they are generally considered “permitted development”. However, you should always check with your local planning authority to confirm any particular requirements in your area. If your home is located in a listed building or conservation area you may need additional consent to install a heat pump. You may also require planning permission if you are intending to install more than one air source heat pump (ASHP) on your property. 

There are also specific conditions that must be adhered to when installing your heat pump. To qualify for “permitted development” your heat pump must comply with Microgeneration Certification Scheme planning standards (MCS 020). If your proposed installation does not meet the required standards, including noise levels, you may need to apply for planning permission. The size of the air source heat pump’s (ASHP) outdoor compressor unit (including housing) must also not surpass 0.6 cubic metres. Another consideration is that the unit must be installed at least one metre away from property boundaries. Installations on pitched roofs are typically not permitted development though it is possible to install a heat pump on a flat roof as long as all parts of the air source heat pump (ASHP) are at least one metre from the external edge of that roof. Your installer will ensure the installation complies with local building regulations.

4.    Designing your system and preparing your home

Your installer will design the entire system, including the heating capacity, equipment location, and distribution networks.

You may have been advised to improve insulation in your home. Proper insulation can significantly reduce heat loss which can reduce the size of the heat pump you need and also your energy bills for operating it. All thermal bridging points should be addressed. Having said that, heat pumps are available to any size and can meet any heat demand. 

Your installer will have checked your pipework. If your existing pipes are too narrow to handle the higher water volume and faster flow rates of the heat pump they may need to be replaced with wider pipes. If you have microbore pipes they are smaller and often made from plastic or copper. They can work with a heat pump but may need to be split to run at different flow rates. You may also need new pipework to connect the heat pump to the hot water cylinder. All internal and external pipework should be insulated to ensure the heating system works well. 

Heat pumps tend to run at a lower temperature than boilers which means they may require larger emitters such as radiators, Air Handling Unit coils etc. for the same heat output. Your heat pump installer will have designed a system that works for you. You won’t be affected if you already have oversized radiators. Some heat pumps operate at boiler temperatures in which case you won’t need to replace your radiators. 

You may also be advised to fit energy efficient doors and windows. Double or triple glazed windows and well-sealed doors can prevent drafts and improve energy efficiency.

In some instances, your installer might recommend Improving ventilation with the installation of a Mechanical Ventilation Heat Recovery system (MVHR) which in a well-insulated, air-tight building, will bring in fresh, filtered air without letting too much heat escape.

The order in which the different jobs are tackled and the materials used can make a big difference to the success of your heat pump. It’s important for your installer to take a “whole house” approach if the retrofit measures are going to work. They need to take on board how all the different elements of the home’s fabric interact with each other and understand that adding an efficiency measure in one part of your home may cause a knock-on effect elsewhere. For example, insulating the walls could lead to condensation and damp.  

Your installer will also need to decide where to best place the outside unit of your heat pump, as part of your system design, depending on what space you have available.

One thing that can make the retrofit much easier is if you choose a refrigerant with a temperature differential that closely matches those used by boilers like the natural refrigerant R290 (propane).

Though there seems to be a lot to consider when designing your system, retrofitting a heat pump can be a lot easier than you might expect. 

5.    Installing the heat pump

Installing an air source heat pump (ASHP) can take between 2 to 5 days to complete depending on the complexity of the fitting. Firstly, if you have an existing heating system like a gas boiler it will be removed. The next step will be to position the outdoor unit in a location that has good air flow and where it can be mounted securely, typically on a concrete pad. The indoor unit is then placed inside your home usually close to your existing heating system. Then the refrigerant pipes that carry heat are connected between the indoor and outdoor units, ensuring proper insulation. At this point the heat pump is connected to the electrical supply. You may need a qualified electrician to complete this part of the installation process. The heat pump is integrated with your existing heating system, including radiators and/or underfloor heating. The installer will also install a compatible thermostat or control system. 

6.    Configuring the system and performing quality checks

Your installer will thoroughly test the system to ensure it is working correctly. The tests include checking refrigerant levels, pressures, and heating performance. The installer will ensure the system meets all required standards. 

Your installer will provide the instructions you need to operate the system, on how to use controls, set temperature settings and maintain it. They will give you documentation that includes details of the installation, equipment manuals and warranty information. A typical air source heat pump (ASHP) warranty lasts between 2 and 10 years, with most manufacturers offering a standard 2-year warranty that can be extended to a longer period with proper installation and regular servicing; some brands may offer warranties up to 10 years depending on the specific model and terms of the extended warranty plan. 

As you can see retrofitting an air source heat pump (ASHP) is perfectly feasible and can be a great way of saving money in the future while transitioning towards green technology.