Air source heat pumps;
a guide for Sussex homeowners

To achieve net zero targets, the UK is replacing gas boilers and oil heating systems with heat pumps.

Heat pumps offer efficient, reliable, low-carbon heating that can reduce energy bills as well as carbon emissions.

However, it is important to get your property ‘heat pump ready’ to make sure you get maximum benefit for your investment, and a BHESCo Energy Survey should be the first step in your heat pump journey.

By Richard Dow

Technical Consultant, MEng, CEng, MSc

Last update: 25th April 2025

By Richard Dow

Technical Consultant, MEng, CEng, MSc

Last update: 25th April 2025

What is an air source heat pump?

An air source heat pump is a device which absorbs ambient heat from the air outside of your property and transfers it to heating and hot water system inside your property. For this reason, an air source heat pump is located externally and adjacent to a property. It looks a lot like an air conditioning unit, and its technology is similar to that used in most refrigerators.

Air source heat pumps can be used to provide heating and hot water, and operate efficiently in all temperatures. They form a major part of the UK Government’s strategy for decarbonising heating, and a number of grants are available to support homeowners who want to install a heat pump. it is important to note that heat pumps are not a new technology. They have been in use for at least thirty years in countries like Germany and Scandinavia which are far more advanced than the UK in terms of decarbonising their heat supply.

A heat pump uses a refrigerant to absorb latent heat in the air, which is then compressed to increase its temperature.

The heat is then transferred to a water system for use in radiators, underfloor heating, or hot water tanks.

The heat is transported around your home through insulated pipes, exactly the same as for a gas boiler.

Alternatively, heat pumps can be connected to electric radiators.

What different types of heat pump are available?

There are three types of heat pump which can be installed:

– an air source heat pump,

– a ground source heat pump,

– a water source heat pump.

The best choice for your property will depend on a number of things, the most important being the amount of space available, the amount of money you have to spend, and what the land around the property is like.

Air source heat pumps are the most common type of heat pump due to their lower cost and comparative ease of installation.

Ground source heat pumps are more complicated to install and usually require deep boreholes to be drilled. You can read more about this type of heat pump at the Ground Source Heat Pump Association website.

Water source heat pumps need to be installed close to a water source of sufficient size and flow to avoid freezing, which can include fresh or sea water. Heat is extracted from the water source and converted for use in the home. Water source heat pumps can often be more efficient than an air source heat pump, but they can also be tricky to install and require more equipment to operate.

CASE STUDY 1: The Montessori Place, Uckfield

The Montessori Place is a school in rural Sussex which is not connected to the gas grid.

Before the school engaged BHESCo to design a new heat and power system, the property relied on heating oil, which is very expensive and very polluting.

BHESCo recommended replacing the existing heating system with a combination of an air source heat pump and a ground source heat pump. Heat is supplied to the property from radiators and underfloor heating.

The system is part-powered by a 27kW rooftop solar power array. Extensive insulation upgrades were included as part of the project.

The energy saving and renewable energy technologies were financed by BHESCo’s network of community investors.

Read the full case study:

Are air source heat pumps efficient?

Heat pumps are a lot more efficient than gas boilers and run on electricity which generally creates lower CO2 emissions per unit than gas. Overall switching your home to a heat pump should reduce CO2 emissions by x4.

Heat pumps are considered to be highly efficient because they produce more heat energy as an output than the amount of energy that is input to power the pump.

A typical heat pump can provide 3 to 4 units of heat for every unit of electricity used to power the heat pump, achieving an efficiency of 300% to 400%.

Heat can be extracted from the air irrespective of the weather and heat pumps can function in temperatures as low as -20^oC.

Heat pump efficiency - what is the COP value (co-efficient of performance)?

The efficiency of a heat pump is measured by its Coefficient of Performance value, or the ‘COP’ value.

If a heat pump has a COP value of 3 for example, then every 1kW of electrical energy used by the heat pump will generate of 3kW of heat.

A typical COP value for a heat pump as a seasonal average is in the range of 2.5 to 4.0. A properly designed and installed system should achieve at least 3.0.

Find out if an air source heat pump is suitable for your home with a BHESCo Home Energy Survey

How much does an air source heat pump cost?

The cost of an air source heat pump is determined by:

– the power output (measured in kilowatts)

– the efficiency rating, known as the ‘Coefficient of Performance’ or ‘COP’ value (energy input : heat output ratio)

Government data from December 2024 states that a typical air source heat pump for a domestic property costs an average of £12,500.

In addition to the cost of the heat pump unit itself you will need to consider the installation costs from a locally certified heat pump professional and possible upgrades to the existing property’s radiators or underfloor heating system.

Micro-bore pipework can add to installation costs. While this may not be a deal-breaker, installation should still be possible with partial pipe upgrades.

Will a heat pump save me money?

A heat pump will definitely reduce the amount of energy required to heat your home – but electricity is around 4 times the price of gas.

Having a high efficiency heat pump, and choosing the electricity tariff carefully can help reduce the running costs and make them cheaper

Low flow temperatures mean low compressor power i.e.. low energy consumption. A constant low temperature operation is recommended .

Gas boilers might save 5% by lowering flow temperatures (to increase condensing) – but heat pumps can save 40% by reducing flow temperatures. So it is more efficient to operate a heat pump for longer and not have to increase temperatures as much.

How to choose the right size heat pump for your property

The most important thing to consider when installing an air source heat pump is to choose the correct size and power of heat pump for your property.

To correctly size a heat pump you must take into account the annual heat demand and the thermal efficiency of the building.

The annual heat demand is a measure of the total volume of kilowatt hours (kWh) of heat that is needed for heating and hot water over an entire year.

The thermal efficiency of a building is measured by its Energy Performance Certificate (EPC).

It is often worth considering making energy efficiency improvements at the same time as installing a heat pump. This will have a big impact on the size of heat pump that is required, which is why it is worth engaging a professional energy consultant before going ahead with any heat pump installation.

Designing an efficient system for your home

System design should minimise pipe lengths and heat the water as directly as possible, (avoiding extras such buffer tanks and low loss headers) will reduce the temperature of water to radiators, improving the efficiency.

Any outdoor pipework and pipework to hot water tank should be well insulated.

Controls should work WITH the heat pump, not against it. Almost always best to use the controller which comes with the heat pump as this will work to keep flow temperatures as low as possible.

Systems like Hive, Nest, Honeywell will normally just switch on and off and can lead to low efficiency operation – best not to use them but can be used if prepared to spend some time adjusting heat pump settings initially.

Save money with a heat pump plus a smart tariff

Having a smart meter means you can get a tariff designed for heat pumps and potentially save money. This could include “Time of Use” tariffs, where the cost of electricity fluctuates throughout the day in relation to supply and demand.

The house can also be warmed up in the afternoon to avoiding heating at peak times, and a heat pump controller can be used to ensure water is heated off-peak.

What government grants are available to install an air source heat pump?

Unlike a gas boiler which produces heat from burning fossil fuels, an air source heat pump generates heat from a renewable energy source (air), and will help the UK to achieve its goal of moving to zero carbon emissions by 2050.

For this reason, there are a number of financial grants available to support property owners who want to install heat pumps.

Boiler Upgrade Scheme (BUS)

The Boiler Upgrade Scheme makes £7,500 available to property owners in Sussex who want to install an air source heat pump.

Applications can be made directly through an energy supplier, or through a qualified local installer.

To qualify for the Boiler Upgrade Scheme homes must have a valid EPC. The Boiler Upgrade Scheme is not available for social housing.

ECO+ Funding

Energy Company Obligation funding (ECO+) to support the installation of a variety of measures that will help to reduce household carbon emissions and energy costs. Measures can include solar panels, heat pumps, and insulation.

Applications for ECO+ funding must be made to our energy supplier, and eligibility is dependent on the EPC of your property and annual household income / benefits received.

The Home Upgrade Grant (HUG)

Similar to ECO+ funding, the Home Upgrades Grant (HUG) provides qualifying households with up to £20,000 to install a variety of energy saving and renewable energy technologies.

The Home Upgrade Grant is administered by local authorities who must submit an application for the funding.

HUG funding is targeted at properties with poor levels of insulation who are not connected to the gas network (e.g. homes who rely on all-electric heating, heating oil, LPG, or coal).

CLOSED - The Renewable Heat Incentive (RHI)

The ‘Renewable Heat Incentive’ (RHI) was a scheme that paid owners of clean heating systems in accordance to the volume of heat that they produce from renewable sources.

This subsidy scheme was similar to the ‘Feed-In-Tariff’ scheme that existed to encourage the uptake of solar power generation.

The Renewable Heat Incentive closed in March 2022.

CASE STUDY 2: The Unity Centre, Lewes

The Unity Centre is a yoga and meditation facility based in the Old Turkish Baths building in Lewes, East Sussex. Before work began, the property was an empty shell with no running water, no heating, and no lighting.

BHESCo were engaged to design a cost-effective and environmentally sustainable heating solution that was in line with the ethical values of the Unity Centre.

Following a detailed site-survey and a careful calculation of the annual heat demands, BHESCo designed a low-carbon heating system powered by a 22kW air source heat pump. Heat delivered throughout the building via an underfloor heating system. Each room has individual heat controls.

Upfront project costs were provided by BHESCo’s network of community investors.

What is the best heating and hot water system to connect an air source heat pump to?

An air source heat pump will not deliver heat to a property itself. Heat is transferred to central heating system and emitted to each room via underfloor heating or radiators.

Underfloor heating

A wet underfloor heating system is generally considered to be the most efficient heat distribution system for a heat pump because heat can be emitted as a lower temperature over a large surface area.

This can be combined with an electric immersion tank to deliver hot water.

Underfloor heating being installed by BHESCo at the Unity Centre. Underfloor heating is an ideal way to deliver the heat generated from an air source heat pump.

Wet central heating

If a property has a wet central heating system, an existing combi-boiler can be replaced directly with an air source heat pump to provide heating. However, a new hot water cylinder will need to be installed to provide hot water.

Electric radiators

An air source heat pump can be connected to an existing electric heating system, with heat being emitted through wall mounted electric radiators.

This is far more efficient and cost-effective than running an electric radiator directly from mains electricity, because of a heat pump’s Co-efficiency of Performance. For every 1 kilowatt hour (kWh) of electricity consumed by a heat pump, it will deliver 4 kilowatt hours of heat (an efficiency of 400%). By comparison, every 1kWh of electricity consumed by an electric radiator will deliver 1 kWh of heat.

Can an air source heat pump be used for hot water?

In addition to delivering efficient heat throughout the property via underfloor heating or radiators, an air source heat pump is also able to meet all hot water requirements needed for taps, baths and showers

Due to their low temperature operation, heat pumps need specially designed hot water cylinders in order to gain maximum performance efficiency.

Compared to the use of fossil fuels such as oil and gas, heat pumps can provide an efficient and environmentally friendly way to meet your property’s hot water needs.

Can an air source heat pump be used for cooling?

Air source heat pumps can be used for cooling, but this can depend on the make and model. If this is something you want for your property, it is important to make sure you install a heat pump that can deliver cooling.

A secondary consideration is how cool air will be transported around the property. The most common type of cooling dispersal system is a heat pump convector / fan coil unit. In some instances underfloor heating systems can also be used for cooling, passing cold water through the piping system to cool the room above.

Can an air source heat pump replace a gas combi boiler?

An air source heat pump can replace a gas boiler, but is not considered to be a like for like replacement. The two systems consist of very different technologies, and generate heat in very different ways. In many cases, replacing a gas boiler with an air source heat pump will require an upgrade to the radiators as well as lagging, pipe insulation, and heating controls.

Can air source heat pump work with existing radiators?

You can use your existing radiators to emit heat from a heat pump, but in many cases it is advisable to replace existing radiators with bigger ones. This is because a heat pump is designed to emit a lower level of heat over a longer period of time, in comparison to a gas fired boiler.

Heat pumps in hard to retrofit homes

For some properties, in particular flats with electric heating, there may not be sufficient room for an air source heat pump. In these cases, a possible solution could be installing a solid state heat pump.

These have one internal heat emitter in each room, but don’t need the external heat pump unit.

These systems can produce 2 units of heat from 1 unit of electricity, so are far more efficient than an electric radiator or electric boiler. Developers of solid state heat pumps are working to improve the efficiencies further.

Key things to consider when installing a heat pump

Whilst heat pumps offer an excellent replacement for existing heating systems, they must not be thought of as a simple ‘like-for-like’ exchange. Here are some key considerations:

Heat pumps are designed to deliver a steady temperature over long timeframes

Although most heat pumps are capable of delivering a high temperature heat when required, they are designed to operate most efficiently at a lower but consistent temperature. This is in contrast to traditional gas boilers, which deliver a rapid blast of high heat when they are fired up. For this reason, it is absolutely essential to ensure that your building is made as thermally efficient as possible in order to contain the heat that is delivered from your heat pump.

Choosing the right heat delivery system

Because of the way in which a heat pump is designed to provide heat, you may wish to review the heat emitting system in your home as well as communal areas. For example, to achieve the optimal performance you may wish to replace existing storage heaters with more efficient radiant panel heaters or an underfloor heating system.

Where will your air source heat pump go?

Under current planning regulations, an air source heat pump must be sited a minimum of 300mm away from a wall.

It must also be no louder than 42 decibels (dB) when heard from the nearest habitable window (bedroom, living room). This can make installing a heat pump in a block of flats a complicated challenge.

Talk to the experts

BHESCo’s Energy Saving Team are here to answer your questions and be your guide on your journey to affordable modern heating.

Benefits of installing a heat pump

The UK Government has identified air source heat pumps as the principal technology underpinning their ‘Decarbonisation of Heating’ strategy.

Some benefits of installing an air source heat pump include:

Heat pumps provide an effective, low-carbon energy solution for a wide range of situations. They are suitable for both modern properties and older homes that have good levels of thermal insulation.
They are powered by electricity, which is much easier to decarbonise than gas or oil heating
An air source heat pump can reduce energy costs by up to 30% compared to an existing oil system, and can reduce CO₂ emissions by up to 60% compared to gas in a new build property.
They are highly versatile and can meet the heating demands of nearly all property types and customer needs.
Government grants for heat pumps are available for up to £7,500
Where possible, savings can be increased even further by powering a heat pump through a combination of solar power and battery storage technology.
Heat pumps are a proven heating solution that has been around for decades, providing a reliable source of heat for millions of homes in some of the coldest counties in Europe like Sweden and Norway.

Should you add insulation to your home before installing a heat pump?

To get maximum benefit from your air source heat pump it’s important to take steps for reducing heat loss in your building. This will reduce heat loss and make it easier and cheaper to maintain a comfortable temperature.

Other benefits of improving the energy efficiency of your building could include:

Minimising the upfront cost of your heat pump, as a smaller model will be needed
Minimising disruption by installing efficiency measures at the same time as heat pump
Improving levels of warmth and comfort and boosting health outcomes
Increasing the value of your property by increasing the Energy Performance Certificate (EPC)
Reducing demands on the local electricity network and avoiding costly network upgrades (which are funded by billpayers)
If your boiler is the only equipment in your home that runs on gas, moving to a heat pump could allow the gas meter to be removed, avoid gas standing charges.

It is important to remember that regardless of the type of heating systems you use, it is absolutely essential for all homes and businesses in the UK to dramatically improve energy efficiency if we are to meet our net zero carbon emissions targets.

Whilst it is true that reducing energy demand through efficiency measures will enable any heating system to achieve optimum performance, installing energy saving measures should be considered as an essential upgrade whether you are replacing your heating system or not.

Is an air source heat pump a low-carbon heat source?

The heat generated by an air source heat pump originates from a naturally renewable source (the air), and is therefore considered as a type of renewable energy.

By combining a heat pump with energy saving measures, renewable energy generation and battery storage technology, homes and businesses can achieve a tremendous reduction in the environmental impact of their heating, and in many cases a corresponding decrease in fuel costs.

This is especially important with regards to the decarbonisation of heating throughout rural villages in Sussex, many of which currently rely on heating oil or Liquid Petroleum Gas.

Heat pumps offer a highly efficient way of generating heat and will play a pivotal role in the decarbonisation of the UK’s heat supply.

Can an air source heat pump work with solar panels?

Yes. Heat pumps are powered by electricity, which could come from a mains supply, solar panels, an energy storage system, or any other type of renewable energy source. Powering a heat pump with solar panels will achieve very low running costs, as we have seen with BHESCo’s community energy project at the Montessori Place School.

Introducing a battery storage system means you can store solar electricity generated in the day for use at night when you may wish to use it to power a heat pump.

Even if you do not decide to install solar panels, you can still achieve great cost savings from battery storage by taking advantage of Time of Use tariffs.

Economics of an air source heat pump without solar

Economics of an air source heat pump with solar

How noisy is an air source heat pump?

The latest heat pump designs operate at noise levels considerably below what is required for Permitted Development in residential settings.

Heat pumps must be located a minimum distance of one metre from your neighbour’s property, and must not exceed 42 decibels when heard from your neighbour’s property (that is the approximate noise of a refrigerator.)

Air source heat pumps in off-gas rural communities

Air source heat pumps offer a particularly attractive solution to off-gas grid communities Sussex villages.

Many of these communities rely on heating oil and LPG, which is expensive, subject to volatile international markets, and harmful to local air quality.

By switching to air source heat pumps, residents will enjoy cheaper prices, cleaner air, and will no longer need to worry about the hassle of organising fuel deliveries.

If you live in the Sussex area and are interested in installing an air source heat pump for your home or business then contact BHESCo to find out how we can work together to improve the energy performance of your property.

We may even be able to help cover the upfront cost of installing your heat pump technology through our innovative ‘Pay As You Save‘ finance initiative.

Our years of experience and technical expertise guarantees that a robust system will be installed to deliver efficient and affordable heat for the benefit of all residents.

Air source heat pumps; a guide for Sussex homeowners

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