Which? published an online heat pump cost savings calculator on 30 April 2025, built with Ambient, an independent not-for-profit organisation supporting electrified heating and cooling, and Dr Jan Rosenow of the Environmental Change Institute at the University of Oxford1. The tool compares running costs against a gas boiler and lets users enter their own annual consumption figure1.
The calculator uses average annual household gas consumption of 11,500kWh and typical boiler efficiency of 85%1. On a standard price-capped tariff, with electricity at 27.03p/kWh and gas at 6.99p/kWh between 1 April and 30 June 2025, a heat pump with a seasonal coefficient of performance (SCOP) of 3.0 saves around £43 a year1. On an Octopus time-of-use tariff at 17.99p/kWh, the same household saves around £331 a year at SCOP 3.0, or as much as £476 at SCOP 4.01. On OVO's Heat Pump Plus tariff, which charges 15p/kWh for the energy used by the heat pump only and a standard rate for all other use, savings reach £428 a year at SCOP 3.0 and more than £500 at SCOP 4.01.
| Tariff basis | SCOP 3.0 | SCOP 4.0 |
|---|---|---|
| Standard price cap (27.03p/kWh) | around £43 a year | not reported |
| Octopus time-of-use (17.99p/kWh) | around £331 a year | as much as £476 a year |
| OVO Heat Pump Plus (15p/kWh for heat pump use) | £428 a year | more than £500 a year |
Upfront costs are also covered. Which? reports that installation can exceed £10,000, with the government-funded Boiler Upgrade Scheme offering a £7,500 discount for homeowners in England and Wales when replacing an existing fossil fuel heating system1. An MCS-certified installer must apply for the grant on the householder's behalf1. In Scotland, the Home Energy Scotland grant and loan scheme offers up to £7,500 for air-source heat pumps, plus £1,500 for households qualifying for a rural uplift, with the remainder potentially available as an interest-free loan of up to £7,5001. Which? notes some suppliers claim prices as low as £500 with a BUS grant, though it adds most installations are likely to cost more once insulation, radiator upgrades and other extras are included1.
"We've released a new online calculator tool, which shows that by switching to the most appropriate electricity tariff, heat pump owners' ongoing energy bills can be lower than those of the equivalent gas or oil boiler."
Why it matters for households
Running costs, not just purchase price, determine whether a heat pump lowers a home's exposure to energy prices. The calculator's figures show the gap between electricity and gas unit rates is the deciding factor: at the capped rate the saving is marginal, while a tariff that discounts heat pump consumption changes the outcome substantially1. Access to those tariffs requires a smart meter recording half-hourly consumption1. Which? warns that savings depend on shifting use away from peak periods, typically 4pm to 7pm, and that households unable to do so may not save money1. It adds that specialist time-of-use tariffs do not appear on energy comparison services1. For a household weighing heat pump versus gas boiler running costs, the tariff choice carries as much weight as the appliance itself.
What happens next
Which? states the calculator will be updated to show new heat pump tariffs as they become available1. No further dated steps are reported.