Calculator · Hot water
Heat-pump running-cost comparison
Compare water-heating energy costs with your demand, rates and efficiency assumptions.
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How this tool works
An illustrative thermal-demand model, not a product forecast. Daily heat is litres × 4.186 × temperature rise ÷ 3600 kWh. Electricity and gas usage allow for the efficiency assumptions; gas uses 3.6 MJ per kWh. Heat-pump electricity is heat divided by COP. Annual figures use 365 identical days.
Standing losses, seasonal efficiency, booster use, installation costs, maintenance and supply charges are excluded. For solar, enter the export value forgone and account for any grid top-up separately. Do not count the whole gas supply charge as saved unless the connection is actually removed.
Sources
One unit of electricity to operate the system, plus two units of heat moved from the outside air, gives three units of heat to the water: an example coefficient of performance (COP) of 3.
A heat pump moves heat. It does not just make it.
Electricity in
1 unit
To operate the system
Heat from air
2 units
Moved from outside air
Heat to water
3 units
An example COP of 3
An efficiency example, not a year-round performance promise.
