Hot Water Cost Calculator
Compare what heating your household's hot water really costs on a gas boiler, an electric immersion heater, or a heat pump.
Estimate only. Estimates based on the litres, occupants, temperature rise and rates you enter — actual system efficiency varies by make, age and installation. Source: Energy Saving Trust, Ofgem.
Your household needs about 3.65kWh a day (1333.71kWh a year) of heat energy to warm this much water.
Annual cost by heating system
| System | Annual cost | Per person | Saving cutting 10L/person/day |
|---|---|---|---|
| Heat pump | £108.92 | £54.46 | £24.20 |
| Gas boiler | £91.88 | £45.94 | £20.42 |
| Electric immersion | £326.76 | £163.38 | £72.61 |
Cutting your hot water cost
- A cylinder jacket costs around £20 and typically pays for itself within a year by cutting standing heat loss from an unlagged tank.
- Fit an immersion timer so it only heats water when you actually need it, rather than keeping a full tank hot around the clock.
- Fix dripping hot taps promptly — a slow drip can waste a surprising amount of already-heated water, and the cost, over a year.
How the three systems compare
Whichever system heats your water, the energy needed to warm it is the same — it depends only on the volume of water and how many degrees it needs to rise, based on water's specific heat capacity. What differs is how much input energy each system uses to deliver that heat: a gas boiler loses some heat up the flue (around 90% efficient), an electric immersion heater converts electricity to heat almost 1:1, and a heat pump moves roughly three units of heat for every unit of electricity it consumes (a seasonal coefficient of performance, or SCOP, of about 3). That's why a heat pump is typically the cheapest to run for hot water and an electric immersion heater the most expensive, even though a gas boiler and an immersion heater are heating exactly the same amount of water.