How to use this glossary
Terms are grouped by where you meet them: the application process first, then the organisations, the technologies, the grant rules, performance and running costs, and finally tax, planning and complaints. Each term links to the page that goes deeper. If you are new to the grant, start with the Boiler Upgrade Scheme explained, then check whether you qualify.
The scheme and its process
- Boiler Upgrade Scheme (BUS)
- The grant scheme in England and Wales that pays £7,500 towards an air source or ground source heat pump, £9,000 in qualifying off-gas oil and LPG homes, £2,500 for an air-to-air heat pump in a home and £5,000 for a rural biomass boiler. Funded by DESNZ and run by Ofgem.
- Voucher
- The approval Ofgem issues to your installer once an application is accepted. It reserves the grant and lasts 3 months, or 6 for ground source.
- Voucher redemption
- The installer claiming the grant from Ofgem after the system is installed and commissioned. Ofgem pays the installer, not you.
- Installer-led application
- How the scheme is designed: the installer, not the property owner, applies for and redeems the grant on your behalf.
- Consent
- Your confirmation to Ofgem, by email, that the installer is applying for you. You have 14 days to respond. It does not tie you to that installer.
- Retrospective application
- An application made after the system is commissioned, allowed within 120 days. Ofgem's guidance treats it as higher risk than applying first.
- Deducted upfront
- How the grant reaches you: the installer takes it off the quote and invoice at the outset, so you pay only the balance.
- Scheme closing date
- The closing date GOV.UK’s grants finder lists: 30 December 2029. Ofgem’s installer guidance gives 31 December 2029 as the last date it can issue vouchers. The budget is set annually and awarded first come first served, so the money can run out before then.
Organisations and standards
- Ofgem
- The energy regulator for Great Britain. It runs the Boiler Upgrade Scheme day to day: approving vouchers, checking installations and paying installers.
- DESNZ
- The Department for Energy Security and Net Zero. It sets scheme policy and eligibility rules and publishes the official statistics.
- MCS
- The Microgeneration Certification Scheme. It certifies installers and products and issues the certificate for each installation. The grant requires an MCS-certified installer.
- MCS certificate
- The document issued for a completed MCS installation. Keep it with your invoice and commissioning papers.
- Consumer code
- A code of practice that installers working with households must belong to for the grant. The approved codes include RECC, HIES and the MCS code (approved 1 June 2026).
- RECC
- The Renewable Energy Consumer Code, one of the approved consumer codes, with its own complaints and dispute process.
- HIES
- The Home Insulation and Energy Systems Contractors Scheme, another approved consumer code.
- Home Energy Scotland
- The Scottish Government-funded advice service that administers Scotland's heat pump grant (up to £7,500) and loan (up to £7,500), which replace the Boiler Upgrade Scheme there.
Technologies
- Air source heat pump (air-to-water)
- A heat pump that takes heat from outdoor air and puts it into water for radiators, underfloor heating and a hot water cylinder. The most common grant-funded system.
- Air-to-air heat pump
- A heat pump that heats indoor air directly, like a reverse-cycle air conditioner. Funded at £2,500 in homes only. It does not supply hot water.
- Ground source heat pump
- A heat pump that collects heat from pipework buried in the ground, in trenches or a borehole. Same headline grant as air source, but dearer to install.
- Ground loop
- The buried pipework, horizontal in trenches or vertical in a borehole, through which a ground source system collects heat.
- Hybrid heat pump
- A heat pump working alongside a fossil fuel boiler. The scheme does not fund hybrids.
- Biomass boiler
- A boiler burning wood pellets, chips or logs. Funded at £5,000 in rural, off-gas properties meeting the emissions conditions.
- Hot water cylinder
- The insulated tank that stores hot water. Most air-to-water heat pump installations need one because they heat water gradually rather than on demand.
- Legionella cycle
- A periodic higher-temperature heating of stored hot water to control legionella bacteria, built into the cylinder controls.
Grant rules
- Off-gas grid
- A property not connected to mains gas. For the higher grant it must also have no gas meter point on record and not be on a heat network. A capped meter still counts as a gas connection.
- Off-gas uplift
- Ofgem's term for the £9,000 band, for applications from 21 July 2026 to 31 March 2027 in off-gas homes replacing oil or LPG.
- Capped (clamped) meter
- A gas meter that has been disconnected but not removed. It still counts as a gas connection when the higher grant is assessed.
- LPG
- Liquefied petroleum gas, stored in a tank or cylinders. Replacing an LPG system in an off-gas home can qualify for the higher grant.
- Heat network
- A system supplying heat to several buildings from a central source. A property connected to one is not off-gas for the higher grant.
- kWth
- Kilowatts thermal, the heat output of a system. Grant capacity limits are 45 kWth for a single system and 70 kWth for multiple heat pumps.
- EPC
- Energy Performance Certificate. A valid EPC is no longer required for the grant (relaxed from 28 April 2026); the installer gives the reference if one exists, otherwise other evidence.
- Self-build
- A home built by or for its first owner. Unlike most new builds, certain self-builds can be eligible for the standard grant, though not the higher off-gas band.
- Social housing exclusion
- Social housing is outside the Boiler Upgrade Scheme.
- ECO4
- The Energy Company Obligation, a supplier-funded scheme for qualifying households. It ends on 31 December 2026.
Performance and running costs
- SCOP
- Seasonal coefficient of performance: the heat a heat pump delivers per unit of electricity over a heating season. A SCOP of 3 means three units of heat for each unit of electricity.
- Flow temperature
- The temperature of the water sent to the radiators. Heat pumps run most efficiently at lower flow temperatures, which is why some radiators are upsized.
- Heat-loss calculation
- A room-by-room calculation of how much heat a building loses, used to size the heat pump and radiators. A quote should be based on one.
- Commissioning
- Setting up and testing the installed system so it works as designed. The voucher is redeemed after commissioning.
- Price cap
- The maximum unit rates and standing charges suppliers can charge on default tariffs, set quarterly by Ofgem. Running-cost examples here use it.
- Time-of-use tariff
- An electricity tariff with cheaper rates at certain times of day. Heat-pump versions can lower running costs for homes that can shift their heating.
Tax, planning and complaints
- VAT Notice 708/6
- HMRC's guidance on VAT for energy-saving materials. Installing a heat pump in a home is 0% until 31 March 2027, then 5%.
- Permitted development (Class G)
- In England, the right to install an air source heat pump on a house without a planning application, if conditions are met, including the MCS noise standard of 37.0 dB(A).
- MCS 020 a)
- The MCS planning standard that sets how heat pump noise is assessed for permitted development in England.
- Assessment position
- The point, such as a neighbour's window, where the noise of a heat pump is assessed against the limit.
- Heat pump grant scam
- An unsolicited offer of a "free" heat pump or a fee to release a grant. The real scheme is applied for by the installer you choose and the grant comes off the quote.
- Quote
- The installer's written price. It should itemise the work and show the grant as a deduction, with the balance you pay.