Gas usually has a lower input price per kWh than electricity, but input energy is not the final product. A fair comparison works out the cost of useful heat delivered by each complete system.
The short answer
For gas, divide the unit rate by the realistic seasonal efficiency of the heating system. For directly charged thermal storage, account for off-peak and peak electricity, standing loss and distribution. For a heat pump charging storage, include the heat pump's seasonal performance at the required temperature.
Separate hot water and space heating
The existing boiler may serve both. Replacing only hot-water storage does not remove the gas standing charge if gas remains for heating or cooking.
Use the tariff actually available
The electricity price cap's single-rate figures do not describe a particular smart or Economy 7 tariff. Use your quoted peak, off-peak and standing charges.
Avoid three common errors
- Comparing electricity and gas input prices without efficiency.
- Applying the cheap electricity rate to energy that charges at peak time.
- Claiming removal of the gas standing charge while another gas appliance remains.
Capital work matters
Running-cost comparison is not total cost. Include boiler replacement avoided, electrical upgrades required and expected maintenance in a separate ownership view.
Carbon is another calculation
Carbon intensity varies with fuel and time. Do not infer emissions solely from the bill result.
Your next step
Ask both proposals to state annual input energy, useful heat and all standing charges. If one quote supplies only a cash total, request the underlying kWh.
Sources
Primary and independent references checked by our editorial team.
- Energy price cap unit rates and standing charges — Ofgem Checked 10 Nov 2026