An air conditioner that heats is a heat pump. It uses electricity to move heat. A gas boiler burns gas to make heat. The graphs use the Energy Saving Trust range for how much heat comes back, and Ofgem’s unit prices for 1 October to 31 December 2026. Each line in quotation marks is theirs, and each card links to their page.
0.250 kWhElectricity at 4 units of heat
0.333 kWhElectricity at 3 units of heat
1.111 kWhGas at a 90% boiler
3.3×Electricity unit price over gas
For 1 kilowatt hour of heat in the room. At 4 units of heat per unit of electricity, the air conditioner uses 0.250 kWh of electricity, which is 6.58p at the Ofgem electricity rate. At 3 units of heat, it uses 0.333 kWh, which is 8.77p. A new A-rated gas boiler, at 90%, uses 1.111 kWh of gas, which is 8.86p. A plug-in heater uses 1.000 kWh of electricity, which is 26.32p.
Air conditionerGas boilerPlug-in electric heater
At 3 units of heat, the air conditioner and the new gas boiler land on almost the same pence: 8.77p against 8.86p. At 4 units of heat, the air conditioner is 6.58p against 8.86p for the boiler. Electricity on this cap is 3.3 times the gas unit price (26.32p ÷ 7.97p), which is why the 3× bar and the boiler bar sit together.
Fuel for 1 kWh of heat
Source: Energy Saving Trust. Three to four units of heat per unit of electricity. An A-rated boiler converts 90% of its fuel into usable heat. In-depth guide to heat pumps
Pence for that 1 kWh of heat
Source: Ofgem Direct Debit average, 1 October to 31 December 2026. Electricity 26.32p per kWh, no VAT. Gas 7.97p per kWh, including 5% VAT. Standing charges left out. Ofgem price cap, 1 October to 31 December 2026
For 1 kWh of heat
Fuel
Amount
Pence
Air conditioner, 4 units of heat
electricity
0.250 kWh
6.58p
Air conditioner, 3 units of heat
electricity
0.333 kWh
8.77p
New gas boiler, 90% of the gas into heat
gas
1.111 kWh
8.86p
Plug-in electric heater
electricity
1.000 kWh
26.32p
One hour, a 2.5 kW room and a 2.0 kW room
Source: Same Energy Saving Trust range, scaled to 4.5 kWh of heat in one hour. Illustration of those sizes running together. In-depth guide to heat pumps
Pence for that hour
Source: Same Ofgem unit rates. At 3 units of heat the hour is 39.48p of electricity against 39.85p of gas. At 4 units of heat it is 29.61p. Ofgem price cap, 1 October to 31 December 2026
Energy Saving Trust
How efficient they are
“With a heat pump, for every unit of electricity you use, you can get three to four times as much heat (300 to 400%) in return. Compare that to a gas or oil boiler. An A-rated boiler should convert 90% of its fuel into usable heat—meaning some of what you pay for is lost.”
“So, if a heat pump has a CoP of 3.0, then it gives out three units of heat for every unit of electricity it uses.”
“However, if you have a newer gas or oil boiler, heat pumps won’t necessarily be cheaper to run. This is because electricity is more expensive per unit compared to gas or oil.”
“Heat pumps don’t normally cost more to run than gas.”
“At current energy prices, running costs for heat pumps are around the same as for a new gas boiler.”
“Also, if you’re replacing an older boiler, heat pumps are cheaper to run. And they beat any other kind of heating system for running costs.”
“Heat pumps are generally around four times as efficient as a new gas boiler.”
“However, heat pumps use electricity. And electricity is currently four times as expensive than gas.”
Words: Energy Saving Trust, fact check dated 1 July 2026. Their “four times as expensive” is that date. Ofgem’s cap for 1 October to 31 December 2026 is 26.32p of electricity against 7.97p of gas, which is 3.3 times. The graphs use the Ofgem rates. Heat pump fact check
Ofgem · 1 October to 31 December 2026
The unit prices on the graphs
“If you are on a standard variable tariff (default tariff) and pay for your electricity by Direct Debit, you will pay on average 26.32 pence per kilowatt hour (kWh). The daily standing charge is 54.83 pence per day. This is based on the average across England, Scotland and Wales. It does not include VAT from 1 October 2026 to 31 March 2027.”
“If you are on a standard variable tariff (default tariff) and pay for your gas by Direct Debit, you will pay on average 7.97 pence per kilowatt hour (kWh). The daily standing charge is 29.68 pence per day. This is based on the average across England, Scotland and Wales and includes VAT at 5%.”
Words: Ofgem. The graphs use the unit rates only. The daily standing charges are left out, because a home that already has electricity and gas pays those either way. A fixed tariff can differ from this cap. Changes to the energy price cap, 1 October to 31 December 2026
GOV.UK · Department for Energy Security and Net Zero
Units of heat
“They can produce around 3 units of heat for every unit of electricity they use. They significantly reduce a property’s energy demand when replacing technologies such as gas boilers.”
Words: GOV.UK, 28 March 2024. That page is about heat pumps which feed radiators or underfloor heating and a hot-water cylinder. The wall air conditioner heats the air in the rooms. Heat pumps explained
Nesta · 3 February 2025
The wall unit, which is air-to-air
“Air-to-air heat pumps also transport and compress heat from the air outside, but transfer it to a home as blown air. This negates the need for radiators or underfloor heating, as well as enabling their use for cooling. They are considered to have similar energy efficiency to air-to-water heat pumps, although there is little evidence of this in practice.”
“They are not able to produce hot water and so require a separate technology, such as an immersion heater, alongside it.”
“Currently, they are not eligible for the Boiler Upgrade Scheme.”
Words: Nesta. The wall air conditioner on the indoor-unit pages is this kind of heat pump. It heats and cools the rooms. It does not heat the hot water, and it is not the Boiler Upgrade Scheme product. Air-to-air heat pumps
This page is the energy and the unit price. It is not an Artifis price. A cold week can sit toward the 3 units of heat, or below the published test figure. The yearly average for one house is calculated for that house. The graphs leave out standing charges, hot water, and any time-of-use tariff. Energy Saving Trust says a heat-pump time-of-use tariff can bring the electricity cost down. These pages do not show everything we can get. We can get any brand, and any size.