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Reference

Heat pump installation glossary

The words that turn up in surveys, quotes and grant emails, each explained in a line or two and linked to the page that uses it.

Figures checked 3 November 2026Sources at the foot of the pagePublished by SEO-DONS LTD, an independent guide

Air source heat pump
A heat pump that takes heat from the outside air through an outdoor unit and uses it to warm water for radiators and taps. Also called air-to-water. Read more
Boiler Upgrade Scheme
The grant for heat pumps in England and Wales, run by Ofgem. £7,500 for most air source and ground source installations, taken off the installer's price. Read more
Buffer tank
A small store of heating water between the heat pump and the radiators that some designs use to smooth how the system runs. Read more
Class C
The permitted development class in England for ground source heat pumps within the grounds of a house or block of flats. Read more
Class G
The permitted development class in England for air source heat pumps: outdoor unit up to 1.5 m³ on a house, 0.6 m³ on a block of flats, plus siting and sound conditions. Read more
Commissioning
The documented switch-on: filling, testing and setting up the system, with the readings recorded. Read more
Competent person scheme
A government-authorised scheme that lets registered installers self-certify building work instead of applying to building control. Read more
Connect and notify
The route where the installer connects the heat pump and then tells the network operator within 28 days, used when the home's new maximum demand is 60A or less and other conditions are met. Read more
Consent (owner confirmation)
The step where the property owner confirms to Ofgem, within 14 days of its email, that the installer is applying on their behalf. Read more
Consumer code
A code of practice an installer belongs to, with standards and a complaints route. Ofgem lists HIES, RECC and MCS for the grant scheme. Read more
Cylinder
The insulated tank that stores hot water for taps and showers. Most heat pump systems need one. Read more
Design flow temperature
The temperature of the water the system is designed to send to the radiators on the coldest day. Lower generally means more efficient, but may need larger radiators. Read more
DNO (network operator)
The company that runs the local electricity cables, different from the supplier that bills you. Read more
Emitters
Whatever releases the heat into rooms: radiators, underfloor heating or fan convectors. Read more
Ground loop
The sealed pipe buried in trenches or boreholes that collects heat for a ground source heat pump. Read more
Heat-loss calculation
The room-by-room estimate of the heat a home loses on a cold day, which sizes the heat pump and the radiators. Read more
Hybrid system
A heat pump working alongside a boiler. Hybrids are not funded by the Boiler Upgrade Scheme. Read more
kW and kWth
Kilowatts, the unit for a heat pump's heat output. kWth (kilowatts thermal) is used in the grant rules, which cap individual systems at 45 kWth. Read more
Maximum demand
The most electricity a home could draw at once. Adding a heat pump raises it, which decides how the network operator is told. Read more
MCS
The Microgeneration Certification Scheme. The grant requires an MCS certified installer, and certification is for each technology. Read more
MCS 020 a)
The MCS sound calculation for air source heat pumps installed under permitted development in England. Read more
MIS 3005-D
The MCS heat pump design standard that certified installers design to. Read more
Permitted development
Work allowed without a planning application, provided every condition in the rules is met. Read more
Redemption
The installer claiming the grant voucher from Ofgem after commissioning. Read more
Retrospective application
A grant application made after the heat pump is fitted. It must be properly made within 120 days of commissioning, and the risk of refusal is the owner's. Read more
Unvented cylinder
A hot water cylinder fed directly from the mains rather than from a tank in the loft. Installing one is building work under the regulations. Read more
Voucher
The grant as approved by Ofgem in the installer's name. It runs for 3 months for air source and 6 months for ground source. Read more
Weather compensation
A control that lowers or raises the flow temperature as the outside temperature changes. Read more

Missing a term? Send it through the form below and we will add it.

Where this page's figures come from

  1. GOV.UK, Boiler Upgrade Scheme: what you can get
  2. Ofgem, Boiler Upgrade Scheme for property owners
  3. legislation.gov.uk, permitted development Class G
  4. MCS, notifying DNOs
  5. MCS, MIS 3005-D heat pump design standard

Read on 3 November 2026. Rules and statistics change: if anything here disagrees with the official page, the official page is right. Tell us through the form and we will correct it.

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