---
title: Heat pumps overview
stability: figures likely to go stale — running-cost comparisons depend on the current Ofgem price cap and electricity/gas tariffs, and grant amounts change; check current numbers before reuse
---

# Heat pumps: the basics

A heat pump is a low-carbon heating system that extracts heat from the outside air (an **air source heat pump**) or the ground (a **ground source heat pump**) and raises it to a useful temperature for a home's heating and hot water, using an electrically driven compressor — the same principle as a fridge in reverse. Energy Saving Trust states a well-installed heat pump typically produces around three units of heat per unit of electricity used, which is why it can cost less to run than its electricity price alone suggests. Ground source heat pumps need buried ground loops or boreholes, so need more outdoor space than air source units — the main practical difference between the two.

## How it differs from a gas boiler

A gas boiler burns fuel to produce a small volume of very hot water (commonly 70-80°C), so radiators can be small and still heat a room quickly. A heat pump normally runs more efficiently at lower "flow temperatures" (often 35-55°C), so it works best in a well-insulated home, with radiators (or underfloor heating) sized generously enough to release enough warmth at that lower temperature. This is why a proper installation includes a room-by-room heat loss survey rather than a like-for-like boiler swap.

## Suitability factors

Energy Saving Trust states heat pumps suit most UK homes, but three things particularly affect performance: insulation level (less heat needed means a lower, more efficient flow temperature); whether existing radiators are correctly sized for lower-temperature operation, which an installer checks and can upgrade where needed; and available outdoor space for the unit or ground loop. A pre-installation survey by an MCS-certified installer assesses this for a specific home, and MCS certification is required to access UK government grant funding.

## Rough cost picture

Government support in England and Wales runs through the Boiler Upgrade Scheme (see the grants-and-funding sheet for amounts), paid as an upfront discount off the installer's quote rather than to the homeowner. On running costs, Energy Saving Trust's guidance is that on a standard electricity tariff a heat pump and gas boiler cost roughly the same to run, while a specialist heat-pump tariff with cheaper off-peak rates can make the heat pump notably cheaper than gas. Running cost also depends heavily on installation quality.

## Sources

- [Heat pumps — Energy Saving Trust](https://energysavingtrust.org.uk/advice/heat-pumps/)
- [Boiler Upgrade Scheme: Guidance for Property Owners — Ofgem](https://www.ofgem.gov.uk/guidance/boiler-upgrade-scheme-guidance-property-owners)
- [Apply for the Boiler Upgrade Scheme — GOV.UK](https://www.gov.uk/apply-boiler-upgrade-scheme)

Facts current as of: 2026-09-20