Boiler Upgrade Scheme technology categories

Scheme rules, eligible technologies and grant amounts were checked on 22 July 2026. They are a dated snapshot of the rules then in force.

The Boiler Upgrade Scheme (BUS) is a grant scheme in England and Wales that pays a fixed amount towards replacing a fossil fuel heating system with a heat pump or a biomass boiler. The grant a property qualifies for depends on which technology category the new system falls into. The scheme recognises four categories, and only one grant is available per property.

The four categories and what each grant is worth

Technology	Grant	Main conditions
Air-to-water heat pump (air source heat pump)	£7,500	Minimum SCOP of 2.8
Ground source heat pump (including water source)	£7,500	Minimum SCOP of 2.8
Air-to-air heat pump	£2,500	Residential properties only
Biomass boiler	£5,000	Off gas grid, rural location, emissions certificate

SCOP measures how much heat a pump delivers across a heating season for each unit of electricity it uses. The 2.8 minimum is determined using the standard the Secretary of State approves.

The grant values are set under the Boiler Upgrade Scheme (England and Wales) Regulations 2022, which the Secretary of State can update. The regulations also hold more granular category structures that could vary the grant by the fuel being replaced or by whether the property is a new build. The simple four-category set is the one in force.

Air source, air-to-water and water source: the same categories under different names

The regulations use “air-to-water heat pump” for the technology that industry and consumer materials usually call an air source heat pump. The two terms describe the same category. The GOV.UK application page reflects this, listing “air source heat pump (sometimes called an air-to-water heat pump)”. The regulatory name is the more precise one, because it separates this technology from the air-to-air heat pump, which is a different category with a different grant.

Water source heat pumps sit inside the ground source category. The regulations define a ground source heat pump as one that draws heat from the ground, which they extend to include water in the ground and surface water. Ofgem’s consumer pages list water source heat pumps as a separate line at £7,500, but the grant and the legal category are the same as for ground source.

Air-to-air heat pumps and the £2,500 grant

The air-to-air category was added by a 2026 amendment to the regulations. An air-to-air heat pump moves heat from outside air and delivers it to indoor air, the way a reverse-cycle air conditioner does, rather than heating water for radiators or underfloor pipes. Its grant is £2,500, against £7,500 for an air-to-water or ground source system.

Several conditions set it apart from the higher-value categories:

• The regulations make it eligible only in residential buildings.
• It carries no minimum SCOP. The 2.8 requirement in the regulations applies only to air-to-water and ground source heat pumps.
• It must still replace the property’s fossil fuel heating and meet the full space heating demand. A system that heats only two or three rooms while a gas boiler stays in place does not qualify. An air-to-air installation looks like adding air conditioning rather than replacing a heating system, so it is easy to assume it qualifies when it heats only part of the home.

An air-to-air heat pump can be installed alongside other electric heating, such as a hot water heat pump, a heat battery or electric heaters. It cannot be paired with any fossil fuel heating.

Biomass boilers and their extra conditions

The biomass category pays £5,000 and is the most restricted. A biomass boiler qualifies only in a rural property that is off the gas grid, and it cannot go in a self-build home. It must deliver its heat through a liquid rather than warming the room it sits in, and it must be able to meet the property’s full space heating and hot water demand. It also needs an emissions certificate showing it meets the scheme’s emissions limits.

Wood-fuelled appliances that also cook face an additional condition about whether the cooking function can be operated separately from the heating and hot water. Not every biomass appliance meets it, so a cooker-boiler needs checking against the detailed eligibility rules rather than being assumed to qualify.

Full heating demand, supplementary heat and capacity limits

Beyond the category-specific conditions, the regulations set requirements that an installation has to meet for any of the grants:

• The air-to-water, ground source and biomass systems must be capable of meeting the full space heating and hot water demand of the property on their own. A system sized to cover only part of the load does not qualify.
• Any supplementary heating must not be fossil-fuelled.
• Capacity is capped. A single system is limited to 45 kWth. A cascade of two or more heat pumps is limited to 70 kWth combined. Heat pumps sharing a ground loop are limited to 300 kWth combined across the loop. Biomass boilers are capped at 45 kWth.

A later heat pump can also connect to an existing shared ground loop rather than needing a ground loop of its own.

What the scheme does not fund

The regulations and guidance exclude several arrangements:

• Hybrid systems that pair a heat pump with a fossil fuel boiler.
• Replacing a heating system that is already low carbon, such as an existing heat pump or biomass boiler.

The temporary £9,000 uplift for oil and LPG homes

From 21 July 2026 to 31 March 2027, an off-gas-grid property heated by oil or liquefied petroleum gas (LPG) can receive £9,000 towards an air source or ground source heat pump, rather than the standard £7,500. The government said it would write to around 200,000 eligible homes about the uplift.

An installation commissioned shortly before 21 July 2026 can still fall within the uplift if the grant application is made in time, because BUS allows an application up to 120 days after a system is commissioned. Anyone timing an installation around the uplift should confirm the current position with their installer, since the amount and the closing date are set by the government and can change.

How a product and installer qualify

Both the product and the installer need certification. Eligible products come from the MCS certified product directory, and the installer must hold MCS certification for the relevant technology.

Ofgem maintains a Product Eligibility List (PEL), a subset of the MCS directory, as an administrative aid for identifying products that could qualify. The list does not check SCOP, so an installer still has to calculate a heat pump’s SCOP separately to confirm it clears the 2.8 threshold. It is also not exhaustive, so an MCS-certified product can meet the scheme’s requirements without appearing on it. A biomass boiler needs its emissions certificate to be listed.

Air-to-air heat pumps are newer to MCS than the other technologies, so the pool of installers certified to fit them under the scheme is smaller than for air-to-water or ground source systems.

How the categories have changed and what is planned

At its 2022 launch the scheme covered air-to-water heat pumps, ground source heat pumps and biomass boilers. A 2024 amendment restructured the grant framework into the category sets described above. A 2026 amendment added air-to-air heat pumps as the fourth category.

Further additions have been announced but are not yet written into the regulations. A heat battery category with a planned £2,500 grant and eligibility for exhaust air heat pumps under the heat pump grant both came out of the government’s clean heat consultation. The scheme has been reported to run to 2030 under the Warm Homes Plan, extending earlier commitments. These are announced directions rather than settled rules, not additions to the categories currently in force.

Related entries

• Boiler Upgrade Scheme voucher process
• Air-to-water heat pumps
• Air-to-air heat pumps
• Ground source heat pumps
• Hybrid heat pump systems
• SCOP performance estimate
• MCS
• Zero-rated VAT on energy saving materials