Each definition links to the page where the term matters most.
- Air source heat pump
- An outdoor unit that takes heat from the air and passes it into water for radiators and a hot water cylinder. The usual kind fitted to houses in the five boroughs. Read more
- Air-to-air
- A heat pump that warms rooms with blown air and does not heat water. Sometimes used in small flats; not covered by the Boiler Upgrade Scheme. Read more
- Boiler Upgrade Scheme
- The scheme that pays £7,500 towards an air or ground source heat pump for owners in England and Wales, or £9,000 for oil- and LPG-heated homes with no mains gas until 31 March 2027, claimed by an MCS certified installer. Read more
- Capped meter
- A gas meter that has been disconnected or clamped. For the higher grant band, Ofgem still counts it as a mains gas connection. Read more
- Class C
- The national permitted development rule for ground source heat pumps within the grounds of a house or block of flats. Read more
- Class G
- The national permitted development rule for air source heat pumps, with conditions on number, size, position and sound. Read more
- Conservation area
- An area a council protects for its character. Class G applies inside one, but no unit may face a road. Read more
- Curtilage
- The land and outbuildings that go with a building. Class G does not apply anywhere within the curtilage of a listed building. Read more
- EPC
- Energy Performance Certificate, rating a home from A to G. The Warm Homes: Local Grant is for homes rated D to G. Read more
- Flow temperature
- The temperature of the water a heat pump sends round the radiators. Lower is more efficient, which is why radiator sizes matter. Read more
- Freeholder
- The owner of a building's structure, including the outside walls and roof of a block of flats. Their agreement is needed for an outdoor unit. Read more
- Heat-loss survey
- A room-by-room calculation of the heat a home loses on a cold day, which sets the size of the heat pump and the radiators. Read more
- Heat network
- A shared heating system serving several homes, often a block of flats, from one plant room. Read more
- Higher band
- The £9,000 Boiler Upgrade Scheme amount for oil- and LPG-heated homes with no mains gas, for applications properly made by 31 March 2027. Read more
- Listed building consent
- Permission needed, alongside planning permission, for work that affects a listed building's special interest. Read more
- MCS
- The certification scheme for heat pump installers and products. The Boiler Upgrade Scheme pays only for MCS certified work. Read more
- MCS 020 a)
- The sound calculation an air source unit must pass to be permitted development, worked out at the nearest neighbouring habitable-room window. Read more
- Retrofit Team
- Sefton Council's team that delivers the Warm Homes: Local Grant in Sefton. Read more
- Semi-detached
- A house joined to one other by a party wall. The most common home in all five boroughs. Read more
- Side passage
- The strip of ground beside a semi-detached house, often the most practical place for an outdoor unit. Read more
- Warm Homes: Local Grant
- Funding, delivered by councils and combined authorities, for energy efficiency and low-carbon heating in lower-income households' homes rated D to G. Read more
How we use place names
"The five boroughs" means Wirral, Sefton, St Helens, Knowsley and Halton. "Merseyside" in the site's name is used loosely to cover them; Halton is outside the old county of Merseyside but inside the Liverpool City Region, and Liverpool itself appears only as a reference row.