How to save energy on hot water

The good news is that cutting hot water energy use does not require an expensive new system. Most of the biggest gains come from changing habits, spending a small amount on insulation, and making sure equipment is set up correctly. This guide works through the key areas in a logical order.

Why hot water matters so much

In a home with a gas or oil boiler, space heating takes the lion's share of fuel use during winter months — but outside the heating season, hot water can account for the majority of energy consumed. In homes with electric water heating or heat pump systems, the same pattern applies. Year-round, hot water is an ever-present demand on your energy supply.

Unlike heating a whole building — where results depend heavily on the building's insulation and design — hot water use responds directly and quickly to the choices made by the people living in the home. A shorter shower, a repaired dripping tap or a well-insulated tank produce savings every single day, in every season.

The areas where most households have the most room to improve are: how much hot water is used (mainly showers and baths), how well the tank and pipes retain the heat already in them, the temperature the system is set to, and how appliances that use hot water are operated.

Showers and showerheads

Showering typically accounts for the largest share of domestic hot water use in households with one or more adults. The two levers are duration and flow rate — and both matter.

Keeping showers shorter is the single most effective habit change. A four or five minute shower uses considerably less hot water than one that runs for ten or fifteen minutes. Small prompts help: a shower timer on the wall, or simply being aware of roughly how long you spend.

An efficient showerhead cuts water use without requiring a shorter shower. Aerated showerheads and flow-restricting heads mix air with the water, maintaining the sensation of a satisfying pressure while using less water — and therefore less energy to heat it. These are inexpensive, widely available and in most cases simply screw onto the existing fitting without tools. See our guide to saving water at home for more detail on choosing and fitting one.

Note that power showers (which use an electric pump to boost pressure) use substantially more water per minute than standard mixer showers. A long power shower can easily use as much hot water as a bath. If you have a power shower and a hot water storage cylinder, this is worth being aware of.

A short shower is also considerably cheaper than a full bath for most households, though it depends on the shower type, flow rate and duration. The bath wins the comfort argument, but a shower wins on efficiency — especially with a good showerhead and a reasonable time limit.

Setting a safe, sensible temperature

The temperature your hot water system is set to affects both safety and energy use, and getting it right requires balancing both.

For homes with a stored hot water cylinder (as opposed to a combination boiler that heats on demand), the cylinder needs to be kept hot enough to prevent the growth of Legionella bacteria, which can cause a serious respiratory illness. The widely recommended minimum for stored water is 60°C (140°F) at the cylinder. Water at this temperature kills Legionella reliably. It is hot enough to scald, so thermostatic blending valves at taps and showers — which mix in cold water before delivery — are recommended for safety, especially in homes with young children or elderly residents.

Setting a storage cylinder below 60°C in order to save energy is not advisable without specific risk-assessment measures in place. The saving is real but the potential consequence is serious. Check the guidance relevant to your country and system type.

For combination boilers that heat water on demand, the domestic hot water temperature can often be set separately from the central heating flow temperature. A setting of around 55–60°C on the tap output side is generally appropriate — no water is stored, so the Legionella risk is lower, but excessively high temperatures still waste energy and create scalding risk.

If your thermostat is set significantly higher than needed — some are left at factory settings well above 60°C — bringing it down to around 60°C can reduce energy use with no loss of safety.

Insulate the tank and pipes

A hot water storage cylinder that is not insulated loses heat continuously, even overnight when nobody is using it. The system then has to reheat the water more often — or you reach for the hot tap and get warm rather than hot water. A proper insulating jacket around the cylinder dramatically reduces this standing heat loss.

1. Measure your cylinder before buying a jacket — check the height and diameter. Jackets are available in standard sizes from hardware and plumbing suppliers.
2. Choose a jacket that is at least 80 mm thick. Thinner jackets are sold but offer much less benefit. Many countries specify a minimum thickness in their energy efficiency recommendations.
3. Turn off the hot water heating circuit (you do not need to drain the tank). If the cylinder is hot, let it cool first or work carefully.
4. Wrap the jacket sections around the cylinder and secure the straps so the jacket fits snugly with no gaps around the base, top or sides. Gaps significantly reduce its effectiveness.
5. Leave the thermostat, immersion heater controls and pressure relief valve accessible — do not cover these with insulation.
6. Insulate the first metre or two of pipe leaving the top of the cylinder with foam pipe lagging. This is where the hottest water sits and where standing losses are highest. The foam tubes split lengthways — press them over the pipe, starting from the cylinder and working outward. Seal the joints with tape.
7. Also lag any hot water pipes running through unheated spaces — lofts, garages, under floors — both to reduce heat loss and to protect against freezing in cold weather.

Laundry, dishwashing and appliances

Washing machines and dishwashers are significant users of hot water, and both offer straightforward opportunities to save.

Modern washing machine detergents — including powder, liquid and capsule formats — are formulated to clean effectively in cold water. Switching to a cold wash for everyday laundry (colours, synthetics, lightly soiled items) can make a meaningful reduction to your hot water demand with no noticeable difference to cleanliness. Hot washes are still appropriate for heavily soiled items, towels and bedding, but as a default? Cold is fine for most loads. See our guide to saving energy at home for more on laundry habits.

Dishwashers are more energy-efficient per item washed than most hand-washing, particularly when run on an eco programme with a full load. A modern dishwasher's eco cycle uses less hot water than filling a sink twice. The key points are: run it full, use the eco setting, and avoid the heated drying option if the machine has one — open the door slightly at the end of the cycle and let the dishes air-dry instead.

Hand-washing dishes is most efficient when done in two basins (one for washing, one for rinsing) rather than under a running hot tap. The running-tap method uses far more water than a filled basin — and most of it is hot. Our guide to dishwasher vs hand-washing efficiency goes into more depth on the comparison.

Fix dripping hot taps

A dripping hot tap wastes both water and the energy used to heat it. Even a slow drip — a drop every second or two — adds up to a meaningful volume over a day, a week, a month. If the drip is from the hot side of a mixer tap, that warm water going down the drain carries energy with it.

The fix is usually replacing a worn washer or cartridge, which costs very little and takes around thirty minutes with basic tools. If you are not confident with plumbing, a plumber can fix a dripping tap quickly and inexpensively. The repair will pay for itself. Do not leave it indefinitely because it is only dripping slowly — it is always dripping.

Check all hot taps in your home — kitchen, bathroom, en suites, utility rooms. Also check the hot water connections under sinks for slow weeps at joints, which can go unnoticed for months.

Timing, solar and heat-pump water heating

If you have a hot water storage cylinder, the timing of when it heats can affect both energy use and cost. Setting it to heat during periods when energy is cheapest (overnight on off-peak tariffs, or during the middle of the day on a time-of-use tariff if you have solar panels) reduces cost without reducing comfort.

If your home has a solar photovoltaic (PV) system, a solar diverter can direct surplus generation into an immersion heater, effectively giving you free hot water when the sun is shining. This is one of the most cost-effective additions to an existing solar system. Our guide to whether solar panels are worth it covers this and other uses of solar generation.

Heat pump water heaters — standalone units that work like a refrigerator in reverse, extracting heat from room air and transferring it to the water tank — are significantly more efficient than a standard electric immersion heater. They are most cost-effective in locations with mild winters and relatively high electricity prices. They require a certain amount of space and ventilation and are not the right choice for every home, but where they suit the situation they can substantially cut the cost of electric water heating. Our heat pumps explained guide covers the principles in more detail.

Solar thermal panels — separate from solar PV — heat water directly using the sun's energy and can provide a significant share of annual hot water in many climates. They are a mature technology but require a suitable roof orientation and, typically, a large enough cylinder to store the solar-heated water. Incentives and installation costs vary widely by country.

Hot water energy checklist

• Keep showers to four or five minutes where possible.
• Fit an efficient showerhead if you do not have one already.
• Check the hot water cylinder thermostat — 60°C for stored hot water.
• Fit an 80 mm+ insulating jacket if the cylinder is uninsulated or thinly insulated.
• Lag hot water pipes in unheated spaces and the first metre from the cylinder.
• Switch the washing machine to cold for everyday loads.
• Run the dishwasher full and on an eco programme; skip heated drying.
• Fix any dripping hot taps without delay.
• Set the cylinder timer to heat at the cheapest or greenest time of day.
• If you have solar PV, investigate a solar diverter for the immersion heater.