Heating water is usually the second largest energy use in a home after heating the rooms, and because so much of it runs on habit there is plenty to trim without anyone going without a hot shower. This guide covers the moves that matter: keeping showers brisk rather than long, setting the cylinder to the right temperature, lagging the tank and pipes, and making sure an electric immersion heater is not quietly running up the bill.
The short answer. Most hot-water savings come from four things: keeping showers short, setting a hot-water cylinder to around 60C rather than scalding, fitting a cylinder jacket and pipe lagging, and not leaving an electric immersion heater on when a gas boiler could do the job. A long power shower can use as much hot water as a bath, so the saving is in the minutes, not the format. For a tanked system, a cylinder jacket is one of the cheapest savings going.
Showers, not baths, and keep them brisk
A bath uses a lot of hot water; a reasonable shower uses far less. The big exception is a long power shower, which can use as much hot water as a bath, so the saving comes from keeping showers brisk rather than from the format alone.
A typical mixer shower uses around 10 to 12 litres a minute, a power shower more. Cutting a daily shower from eight minutes to five, across a household, adds up to a meaningful amount of water heated over a year. The energy to heat shower water is the cost, whether that energy is gas or electricity.
This is where the type of shower matters. An electric shower heats with electricity at 26.11p per kWh, so a 9kW unit costs about 39p for a ten-minute run. A mixer shower fed by a gas boiler heats the water with gas at 7.33p per kWh, so the same heat costs roughly a third as much. A low-flow showerhead cuts the litres without the shower feeling weak, and works on either system.
Set the right cylinder temperature
A hot-water cylinder set far hotter than you ever use it just loses more heat standing there, and you end up mixing in cold at the tap anyway. Around 60C is the usual recommendation: hot enough for safety against legionella bacteria, but not needlessly scalding.
Setting it much above that wastes energy in two ways. The hotter the water, the faster it loses heat to the surrounding air while it sits in the tank, so you reheat it more often. And you cannot use water that hot directly, so you blend in more cold at the tap, which means you heated water you never needed that hot.
If your cylinder feeds the heating system through a coil, the system or tank thermostat usually sits on the side of the cylinder, and many older ones are set higher than they need to be out of habit. Turning it down to 60C is a free change that you make once. If you have an unvented or mains-pressure cylinder you can leave the safety controls alone and just adjust the stat to the temperature you actually use.
For a combi boiler there is no tank, so the equivalent saving is simply not running the hot tap longer than you need, and setting the boiler's hot-water temperature sensibly. A combi heats on demand, so the waste is in water run down the drain, not in a tank cooling overnight. Fixing a dripping hot tap matters here too, since every drop is water you paid to heat going down the drain.
Insulate the tank and the pipes
If you have a hot-water cylinder, a proper insulating jacket is one of the cheapest savings in the whole house. It stops the heat you have paid for leaking away while the tank sits there between uses. A modern cylinder usually has factory foam, but an older copper tank with a thin or missing jacket can lose a surprising amount, and an 80mm jacket costs little and pays back within months.
Lagging the exposed hot-water pipes near the cylinder helps too, keeping the water hotter for longer between the tank and the tap, so you waste less running the tap to clear cold water. Foam pipe lagging is cheap, pushes on by hand and needs no tools beyond a knife to cut it to length. Concentrate on the first metre or two of pipe leaving the cylinder, and any pipework running through a cold space such as a loft or under the floor, where the heat loss is greatest. The full job is covered in cylinder jacket and pipe lagging.
| Measure | Rough cost | Typical annual saving |
|---|---|---|
| Cylinder jacket (older tank) | £15 to £30 | £35 to £70 |
| Hot-water pipe lagging | £10 to £20 | £10 to £20 |
| Low-flow showerhead | £10 to £25 | £30 to £60 |
| Shorter showers (3 min less) | Free | £40 to £80 |
At 7.33p per kWh gas and 26.11p per kWh electricity, Ofgem cap July to September 2026. Savings vary with system, fuel and household size. Worked examples; check your own setup.
Mind the immersion heater
An electric immersion heater is an expensive way to make hot water, because it heats with electricity rather than gas. Heating a full cylinder from cold with a 3kW immersion can take two to three hours and use 6 to 9 kWh, costing £1.50 to £2.40 a tankful at current rates, against roughly a third of that on gas.
If your immersion is a backup to a gas boiler, the common and costly mistake is leaving it quietly switched on, topping up the tank with pricey electricity when the boiler would do the job for less. Check the switch and the timer: the immersion should be off, or set to a cheap Economy 7 night rate, unless the boiler is out of action.
If you are on Economy 7 and rely on the immersion, heating the tank overnight on the cheap rate roughly halves the cost compared with the day rate. Run the figures through the running cost calculator and the immersion's appetite is obvious. For homes with solar panels, diverting surplus generation to the immersion is a way to make otherwise exported electricity heat your water for nothing.
Going further: solar and heat-pump water heating
If you have already done the cheap fixes, there are larger steps for hot water specifically. Solar water heating uses roof panels to pre-heat the cylinder in the warmer months, cutting the gas or electricity the boiler needs; see solar water heating for whether it stacks up. A solar PV system with an immersion diverter does a similar job using electricity rather than dedicated hot-water panels.
For most households, though, the order is simple: short showers and the right cylinder temperature first, then a jacket and pipe lagging, then watch the immersion. Those cost little or nothing and capture most of the saving. The bigger kit only makes sense once the basics are done, and it sits alongside the wider heating measures that dominate the bill.