Terms, A to Z by topic
Grouped roughly as you meet them: the scheme and its process first, then the organisations, the technologies, the grant rules, and finally tax, planning and running costs.
- Boiler Upgrade Scheme (BUS)
- The government grant scheme in England and Wales that takes £7,500 off an air source or ground source heat pump (£9,000 in eligible off-gas oil and LPG homes), £2,500 off an air-to-air heat pump and £5,000 off a biomass boiler. Run by Ofgem for DESNZ.
- Voucher
- The grant, in the form Ofgem issues it to the installer after approving an application. It is valid for 3 months (6 for ground source).
- Voucher redemption
- The installer claiming the grant from Ofgem after the system is installed and commissioned. Ofgem then pays the installer.
- Installer-led
- The scheme’s design: the installer, not the property owner, applies for and redeems the grant. You cannot apply yourself.
- Consent
- Your confirmation, when Ofgem emails you, that the installer is applying on your behalf. Required within 14 days. It does not commit you to that installer.
- Retrospective application
- An application made after the system is commissioned. Allowed within 120 days of commissioning, but Ofgem warns it carries extra risk.
- Ofgem
- The energy regulator for Great Britain. It administers the Boiler Upgrade Scheme: approving vouchers, checking installations and paying installers.
- DESNZ
- The Department for Energy Security and Net Zero, which sets the scheme’s policy and eligibility rules and publishes its statistics.
- MCS
- The Microgeneration Certification Scheme. It certifies installers and products, issues the certificate for each installation and, since the April 2026 regulations, is the only certification the grant accepts.
- MCS certificate
- The document issued for a completed MCS installation. Keep it with your invoice and commissioning papers.
- Certification body
- The organisation that assesses an installer for MCS certification. Shown on the MCS installer search.
- Consumer code
- A code of practice approved by the government that installers working with consumers must belong to. For this scheme: RECC, HIES, or MCS’s own code (approved 1 June 2026).
- RECC
- The Renewable Energy Consumer Code — one of the consumer codes an installer can belong to.
- HIES
- The Home Insulation & Energy Systems Contractors Scheme — another approved consumer code.
- Air-to-water heat pump (air source heat pump)
- 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 (and can cool) indoor air directly — what most reverse-cycle air conditioning units are. Funded at £2,500 in homes only, if it replaces the existing heating. Does not provide hot water.
- Ground source heat pump
- A heat pump that collects heat through pipes buried in trenches or a borehole. Same grant as air source; dearer to install.
- Shared ground loop
- One ground loop serving several properties, each with its own heat pump. Capacity limit 300kWth.
- Hybrid heat pump
- A heat pump working alongside a fossil fuel boiler. Not funded by the scheme.
- Biomass boiler
- A boiler burning wood pellets, chips or logs. Funded at £5,000 only in rural, off-gas properties with an emissions certificate; not in self-builds.
- kWth
- Kilowatts thermal — the heat output capacity of a system. Grant limits: 45kWth for a single system, 70kWth for multiple heat pumps.
- SCOP
- Seasonal coefficient of performance: the average heat a heat pump delivers per unit of electricity over a heating season. SCOP 3 means three kWh of heat per kWh of electricity.
- Flow temperature
- The temperature of the water a heating system sends to the radiators. Heat pumps are most efficient at lower flow temperatures, which is why radiators are sometimes upsized.
- Heat-loss survey
- A room-by-room calculation of how much heat a building loses, used to size the heat pump and radiators. Part of a proper MCS design.
- Commissioning
- Setting up and testing the installed system so it works as designed. The voucher must be redeemed after commissioning, within its validity period.
- Off-gas grid
- For the uplift: a property not fuelled by mains gas (a capped or clamped meter counts as gas), with no gas meter point on record, not on a heat network and not a new build.
- Uplift (uplifted grant)
- Ofgem’s term for the £9,000 grant for off-gas properties replacing oil or LPG, available for applications properly made from 21 July 2026 to 31 March 2027.
- Capped or clamped meter
- A gas meter that has been disconnected but not removed. It still counts as a mains gas connection for the uplift.
- LPG
- Liquefied petroleum gas, stored in a tank or bottles. Replacing an LPG system in an off-gas property qualifies for the higher grant.
- Heat network
- A system supplying heat to several buildings from a central source. A property attached to one is not off-gas for the uplift.
- EPC
- Energy Performance Certificate. No longer required for the grant since 28 April 2026; if one exists, the installer gives Ofgem its reference number.
- Self-build
- A home built by, or for, its first owner and never owned by a business. Eligible for £7,500, not the uplift and not biomass.
- Permitted development (Class G)
- In England, the right to install an air source heat pump on a house without a planning application, within limits including the MCS noise standard of 37.0 dB(A).
- MCS 020 a)
- The MCS planning standard for air source heat pumps, which sets the noise assessment method and limit used for permitted development in England.
- VAT Notice 708/6
- HMRC’s guidance on VAT for energy-saving materials. Heat pump installation in homes is 0% until 31 March 2027, then 5%.
- Price cap
- The maximum unit rates and standing charges suppliers can charge on default tariffs, set quarterly by Ofgem. Used on this site for running-cost examples.
- Time-of-use tariff
- An electricity tariff with cheaper rates at certain times. Heat-pump versions can cut running costs significantly, according to the Energy Saving Trust.
- Home Energy Scotland Grant and Loan
- Scotland’s heat pump support, separate from the Boiler Upgrade Scheme.
Missing a term? Use the form below to tell us and we will add it.