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The short answer
Heating water takes a lot of energy. Our calculation for an 8-minute shower at 8 litres a minute (64 litres, heated from 10°C to 40°C) needs about 2.2 kWh of heat. With a boiler turning about 85% of the gas into heat, that's about 2.6 kWh of gas, or 21p at today's price of 7.97p per kWh.
A bath with 100 litres of water at 40°C needs about 4.1 kWh of gas, or 33p.
| Hot water | Gas used | Cost | |
|---|---|---|---|
| 5-minute shower | 40 litres | 1.6 kWh | 13p |
| 8-minute shower | 64 litres | 2.6 kWh | 21p |
| 12-minute shower | 96 litres | 3.9 kWh | 31p |
| Bath | 100 litres | 4.1 kWh | 33p |
These are our own estimates. Power showers and rainfall heads can use 12 litres a minute or more, which costs more.
Gas boiler vs electric shower
An electric shower heats only the water you use, very efficiently, but electricity costs about three times as much as gas. A 9.5 kW electric shower running for 8 minutes costs about 33p, compared with 21p for the same shower from a gas boiler. Gas usually wins. See electric shower running costs.
Ways to cut the cost
- Take shorter showers. Cutting 2 minutes a day saves about £19.10 a year per person.
- Fit an eco shower head. Lower flow means less hot water.
- Turn the water temperature down a little. On a combi, Nesta suggests setting hot water to around 42°C if you only use it for washing. On a system boiler, keep the cylinder at 60°C.
Sources: Nesta, Government in-situ boiler study, Octopus Energy tariff data.