Domestic air source heat pumps

Air source heat pumps are electrically powered systems that transfer heat from the outside air (even low-temperature air) into a building to provide heating and, in some cases, hot water.

You can make your home more energy efficient and reduce your carbon footprint by replacing your gas boiler with a heat pump.

This consumer guide is for people living in the UK who are considering replacing/changing their existing domestic heating system.

It does not apply to:

• new build structures
• homes that already have a heat pump system that has been professionally designed to meet the needs of the occupier
• ‘ground source’ heat pumps – these have different design considerations, including a focus on the external area(s) where the ground collector will be located.

The term ‘heat pump’ in this guide refers to an air source heat pump.

Is my property suitable for a heat pump?

Before deciding to install a heat pump in your home you will need to consider whether it’s right for your circumstances and your property. Some factors to think about are the following.

Your existing heating system

If your home has a pure electric (dry) heating system, this is not compatible with a heat pump.

Be aware that installing a new wet piped heating system will

• be more expensive
• take longer and
• be more disruptive.

When your existing electric heating system is due for replacement, you should consider what will meet your needs best. Although electric heaters are 100% efficient, heat pumps may be more cost effective to run. You can also lower costs by using heater controls, making more effective use of rooms and adding retrofit appliances like photovoltaic panels and battery storage.

Your existing boiler

The long-term goal is to reduce consumption and carbon emissions.

If you have a relatively new boiler (gas or electric), i.e. under 5−7 years old, prioritising maintaining your existing boiler saves material embodied carbon (carbon used to make the boiler). However, this doesn’t reduce carbon emissions (carbon produced by using the boiler).

A well-maintained boiler can last 20−30 years or longer, but it will be less efficient than a new one.

Maintaining an existing boiler until the end of its service life is more financially viable for most people, rather than taking out a functional and efficient boiler to replace it with a new heat pump. But a gas boiler cannot be deemed more sustainable than a heat pump due to its use of fossil fuels.

Replacing prematurely does cost resources and money and increases carbon emissions through everything associated with the manufacture, delivery and installation of new products (called scope 3 emissions).

But the savings of a heat pump may outweigh these factors in as little as 12 months.

The most appropriate option will vary on a case by case basis, and an installer’s calculations will be bespoke to your situation, so ask for their advice. 

Does your home have the necessary space?

Heat pumps require space, both indoors and outdoors. The heat pump unit sits externally, either on the ground alongside the property or wall mounted. The size of the unit depends on the size of the property it is heating, and you will also need space either side for air circulation.

No one wants to fall out with their neighbours, so carefully consider where the heat pump will be located and discuss with your neighbours first. Heat pumps generate a similar amount of noise to a fridge, so in summer with the windows open noise could be a problem.

If you have no outside space or a very small yard/garden, the property is likely unsuitable for a heat pump. This typically affects leasehold properties such as flats.

However, you can discuss potential options with your block management company and reflect on a whole-building approach. There may be alternative solutions that can help the collective block of leaseholders, rather than acting in isolation for each individual flat. Consent will be required from the building owner/manager.

If you currently have a combination boiler for heating and hot water, you will need space for a new hot water storage cylinder or localised small electric water heaters at water outlets, e.g. sinks (under or over) and showers.

Is the incoming electrical power supply sufficient?

Most homes have a single-phase electricity supply, up to 100 amps. However, electricity supply may be an issue for the wider neighbourhood or the locality. This typically affects rural areas more than urban areas.

If there is insufficient capacity in the local area, this is not something you can address. Your utility provider will determine the feasibility of upgrading any local or regional electrical infrastructure such as substations. Some factors are simply outside of your control.

Do you live in a flood risk area?

A heat pump unit typically sits externally on the ground for ease of access for maintenance. If you live in an area prone to flooding, the unit would need to be raised off the ground. The height required may impact the feasibility of installation and future maintenance requirements. Consider the risks of flooding prior to installing.

See RICS’ consumer guide on flooding for more information.

Whole-building approach helps with planning and decisions

A new heating system is a large investment and shouldn’t be considered in isolation. A whole-building approach considers all aspects of a building to find a range of effective solutions that save energy and carbon, provide a safe and comfortable indoor environment, and in the case of heritage buildings, considers their heritage significance.

RICS advocates for a whole-building approach when considering adapting buildings for a sustainable, carbon neutral future. Installing a heat pump could be just one part of a wider scheme of renewable energy integration, such as

• electricity generation (solar (photovoltaic) panels)
• water heating (solar thermal panels, heat pumps, biomass boilers, etc.)
• insulation and draught-proofing
• ventilation and indoor air quality upgrades
• water conservation (grey water systems)
• space heating.

But a whole-building approach does not mean doing everything all at once.

You may prefer to carry out one or two small-scale interventions and do others, or parts of others, when opportunities arise and budgets allow.

This approach allows owners and occupants to plan how best to carry out the work and make informed decisions.

RICS advocates that small-scale interventions should be considered before more substantial ones. In the case of heritage buildings such as listed buildings, these should be reversible and maintainable where possible.

Get heat pump ready

If you think you shouldn’t consider a heat pump yet, get ‘heat pump ready’ with small-scale interventions as and when opportunities arise.

• You could replace microbore (very small/thin diameter) radiator pipework with standard 15mm pipework next time you’re replacing floor coverings (and your radiator pipes are under the floor boards), or if redecorating (and your pipes are wall mounted).
• Or consider leaving new pipework exposed so you and the pipes benefit from the heat in the room.
• Consider the size of radiators. If you have single panel radiators, you may need to change to double panel radiators, as heat pumps run at lower temperature water.
• If you already have double panel radiators, you may have to upgrade to bigger radiators. However, you will only know if you need to change radiators after professional calculations.
• When doing an electrical rewire, install a larger consumer unit with spare capacity for more electrical systems in your future home. A larger consumer unit will cost marginally more than installing the minimum necessary, however, it will save you more in the future as having the spare capacity will mean new appliances can be wired in more easily - think photovoltaic panels, electric car charging port, electric cooking appliances, etc.

• Alternatively, the heat pump installer may want to install their own small, dedicated consumer unit so that if an electrical fault occurs, the heat pump circuit is clearly separated from the existing house electrics. So also consider the need for extra space round your main consumer unit.

Costs

*Costs accurate at the time of writing (2025)*

Upfront costs

For a home with a typical gas boiler and with radiators and pipework already installed, the cost of installing a heat pump can range from £12,000 to £15,000. However, there are grants available of up to £7,500, so the typical upfront cost ranges from £4,500 to £7,500. Note that these figures include the typical costs of installing a new hot water cylinder, new insulated pipework and upgraded radiators and are not the cost of the heat pump only.

In comparison, if you’re replacing an existing gas boiler heating system with a new gas boiler, with no change to your existing heating distribution system, the costs can range from £3,000 to £4,500 depending on whether the boiler can sit exactly where the old one sat and any necessary pipework changes.

Running costs

The costs of running a heat pump and a traditional gas boiler are similar. You may need to run the heat pump for longer to reach the desired room temperature, however, as the heat pump is three to four times more efficient, the energy costs are similar.

• For a heat pump, 1kWh of electrical energy generates 3−4kWh of heat output.
• For a typical gas boiler, 1kWh of gas energy generates less than 1kWh of heat output.
  
  

Electricity prices per kWh are currently about four times more than gas (2025 prices), so anyone saying as part of their heat pump sales pitch that you'll save money may not be entirely correct.

However, you can reduce the price you pay for electricity by:

• generating it in different ways, e.g. by adding photovoltaics panels and battery storage. This can be part of a whole-property/-house plan.
• signing up to a smart energy tariff, i.e. using more electricity at designated times when the price is cheaper and storing it in batteries for later use.
  
  

But beware! Installing photovoltaics panels and battery storage are additional costs which are not included in this consumer guide.

Green electricity tariffs also help you reduce your environmental impact.

Remember that energy costs fluctuate, so running costs can be difficult to predict. External factors, such as Brexit and the Ukraine war, affect gas prices, and these have a knock-on effect for electricity costs because they are intrinsically linked to gas costs due to how we currently generate electricity in the UK. 

Taxes and grants

The installation and running costs are not the only factors to consider when buying a new heating system: taxes and grant funding change frequently.

Obtaining quotations specific to your property is the only way to compare costs.

Before proceeding with any works:

• confirm the capital costs
• understand the running costs
• ensure grants are still available.

Also, look out for future government announcements and don’t forget to investigate any additional (carbon) taxes imposed on fossil fuel installations.

Get the right size of heat pump

Your installer should provide calculations based on your property and needs, to advise on the size of the heat pump. They will look at the sizes of your walls, rooms, windows and radiators, as well as considering any existing insulation.

Get the size that’s right for your home – bigger isn’t always better. A larger heat pump may be less efficient than a smaller heat pump and would cost more to install and run.

You will be relying on your installer, who is also designing the system, to provide calculations and size the heat pump correctly. However, the nature of this ‘design and build’ type contract means that installers are not impartial and may have a commercial incentive to install a larger, more expensive system.

RICS advises consumers to do their own due diligence, research what size units they are likely to need and have a frank and honest discussion with the installers.

Obtaining at least three quotations (with associated calculations), is considered good practice for any building work of significant costs. Obtain recommendations and examples of previous successful installations. Consider who is advantaged by the recommended system.

It is not an advantage to the consumer to have an oversized system.

Older houses

Heat pumps can work in most properties regardless of age or construction type.

Britain has some of the oldest housing stock in Europe, but that’s not all bad. Heat loss concerns with traditional/heritage buildings do not mean they are incompatible with heat pumps. Although a heat pump runs cooler than a traditional boiler, that doesn't mean the house will be cold. Good design and installation is critical, and understanding how to work the system and compensate for this difference is key.

Do simple things first to make a positive difference in your home before making expensive, significant alterations. A whole-building approach includes simple things such as draught stripping around doors and windows, adding insulation and upgrading windows, which will help get your property ‘heat pump ready’.

Be mindful not to block ventilation designed for combustion appliances like a stove or boilers.

Risks and expectations

Understanding your heating system

A heat pump is a different system to the gas boiler that you have been used to, and learning how to operate it is critical.

The MCS (which provides certification for heat pump installers) states in its best practice guide that:

Heat pumps operate at a lower temperature than traditional gas boilers to achieve higher efficiency. They are most efficient running at 55C. Heat pumps are less efficient at higher flow temperatures, although they can operate at the same temperature as traditional boilers. It all depends on the design and operation of the system.

If the system is designed to run at a lower temperature, you may have increased the size of your radiators during installation, or your installer may advise you to run the heating for a longer period of time to heat your home. Each design is bespoke and you should ask your installer for advice.

Another advantage is that lower-temperature radiators result in a more comfortable, consistent environment. Unlike traditional gas boilers, you do not get the peaks and troughs in room temperature.

You should be aware of this temperature expectation. Some installers turn the temperature of the system up because customers complain that the radiators aren't as hot as they are used to. However, it is crucial to understand how the system is intended to operate, i.e. operation at traditional (higher) temperatures will result in lower efficiency and higher running costs, but lower temperatures can be satisfactory based on (larger) radiator and room size calculations.

Legionella

If you are used to a combination boiler for heating and hot water, you may not be aware of the risks of legionella. Changing to a separate heating system and hot water storage tank for hot water has risks to be managed.

Legionellosis is a lung infection caused by legionella bacteria. It causes fever, headache, cough and shortness of breath.

Legionella is not a substantial risk for a domestic heating system. It is, however, a risk for the domestic hot water system.

You should speak to your installer about how to mitigate the risk of legionellosis because methods will vary for each installation. Generally, the heat pump system should heat the cylinder hot water to around 60C once per week.

Servicing

Understanding the optimisation of the system will help you get the best out of it. But don’t be afraid to question and challenge an installer. If the system isn’t functioning as expected, ask the installer to come back, as the system may need rebalancing and optimising again.

Using an RICS member

While building services typically fall outside of the expertise of a building or residential surveyor, retrofit insulation, construction defects and condition fall outside of the expertise of a heat pump installer.

There are many types of RICS qualified surveyors with differing competencies and skill sets. A chartered building or residential surveyor can assist you with a whole-building approach.

To mitigate risks from unintended consequences, such as a construction defect happening as a result of the heating alterations, a building or residential surveyor with retrofit experience can help manage and advise on the project as a whole so you don’t face this significant challenge alone.

As part of a strategic goal to lead and influence on sustainability, RICS is committed to equipping the profession to adapt, upskill and respond to the challenges and opportunities that sustainability poses. Find a surveyor working to the RICS residential retrofit standard to assist with your project.

If selling or buying a house in the UK with a heat pump, disclosure of heat pump information would be included in National Trading Standards material information statements. Further information can be found on the trading standards website, and it’s recommended to use an RICS-regulated estate agent.

Schemes, further guidance and government financial incentives

There are several schemes, guides and government financial incentives available in the UK to help households improve their energy efficiency, monitor energy performance and generate renewable energy. 

• Carbon Trust
• energyadvice.scot (Scotland) 
• Energy Saving Trust
• Good Homes Alliance
• Heat pumps (GOV.UK)
• Help to Heat (GOV.UK)
• The Housing Executive – Energy Efficiency Grants (Northern Ireland)
• Nest (Wales)
• RICS
• Simple Energy Advice
• Which?

Speak to your current energy provider, who may have schemes available to support you, including advice on tariffs.

For advice specific to historic buildings, also see the Historic England advice page and webinar recording.