How to use hot water efficiently

In this guide you’ll find answers to the following questions:

  • How can I heat water in my home more cheaply?

  • Which type of shower is most efficient?

  • Are there any quick and inexpensive (or even free) ways to lower my hot water costs?

  • When’s the best time to replace my hot water system?

  • How can I heat my water using solar power?

  • Hot water: FAQs

How can I heat water in my home more cheaply?

Traditionally, most homes heated their water using their existing central heating system, storing and heating a finite amount of water in a hot water cylinder.

An alternative to using the central heating system – and one found in most homes as a backup should the central heating go down – is the immersion heater. These are electric water heaters contained inside an insulated hot water cylinder. The electric elements heats the water inside the cylinder in the same way a kettle does. These can be switched on and off as demand requires it.

In recent years, this kind of arrangement has been supplanted by combi boilers, which heat hot water on demand. Today’s combi boilers have been designed as much with efficiency in mind as they have convenience, making them a better choice for most households.

Alongside combi boilers are electric showers that heat the water as it passes through the shower unit rather than relying on the house’s hot water supply. These cost around £500 but are again more efficient than traditional heating methods.

As we’ll discuss below, if you can afford the upfront cost, it’s also possible to heat your water using solar panels. While the initial cost is high, given that over 10% of your energy bill goes on heating your water, you can soon recoup the costs.

All the above looks at the cost of heating the water, but how much water you consume also plays a part – not only through making greater demands on your water-heating system, but also through your water bills. If you’ve not done so already, you could save money by switching to a water meter to help track usage and identify potential savings.

Which type of shower is most efficient?

There are – broadly speaking – three types of shower:

Electric shower

This popular type uses your house’s electricity supply to heat the water instantly as it passes through the mains unit. Typical water consumption is 62 litres of hot water for an eight-minute shower.

Power shower

Another popular type, this draws hot water from your hot water cylinder, which it mixes with your cold-water supply, so relies on a central heating system or immersion heater. Some types can consume up to 136 litres for each shower.


This type of shower is less popular, and like the power shower draws hot and cold water from your existing systems. Lower-end mixers are connected directly to your taps with no electric unit involved. They’re best suited to homes with high water pressure but consume less water than both power showers and baths (which consume 80 litres).

While gas costs less than electricity, electric showers are still far more efficient than relying on your hot water system.

Are there any quick and inexpensive (or even free) ways to lower my hot water costs?

The simple fact of paying attention to the amount of hot water you’re using will help you adjust your behaviour to reduce your consumption and lower your household bills. Keep an eye on your water meter to measure consumption and see the effects of any changes you try. Then try some or all of the following:

  • Get in the habit of only switching on the shower to rinse off after washing – this could have the biggest single impact on your hot water usage if you’re only switching on the shower for a minute or two each time instead of 5-8 minutes.

  • Adjust your showerhead to reduce the flow of water – look for eco-friendly showerheads that mix water with air to replicate the sensation of a powerful jet of water while cutting consumption.

  • Review your boiler’s settings – make sure you’re not leaving it on all day, and instead set times to coincide when your household uses most hot water. Consider fitting a timer if you don’t already have one.

  • If you have an Economy 7 or Economy 10 tariff, use the immersion heater at night when rates are cheaper. 

  • Reduce your boiler’s thermostat to 65 or even 65 degrees Celsius.

  • If you’ve not already done so, fit an insulating tank jacket to your cistern to lock in the heat. If your cylinder is in an airing cupboard, pack it with blankets, towels, and pillows to add additional layers.

  • Cut the amount of water you use when washing up: fill the basin once, then wash the cleanest items first (typically glasses, mugs and then cutlery) to maximise the use from a single bowl. Rinse in a separate bowl if you have the space rather than under the running tap.

When’s the best time to replace my hot water system?

If your hot water cylinder is over ten years old, now might be a good time to replace it with a new, well-insulated model. The best can keep water warm for up to two days.

Most boilers are designed to last around fifteen years – if yours needs replacing, now is a good time to consider replacing it with an instant-on combi boiler.

How can I heat my water using solar power?

There are two ways to heat water in your home using solar energy. The obvious solution is to invest in a dedicated hot water solar system. Solar water heating systems use solar panels that harness the warmth of the sun to heat liquid that’s passed through them before it ends up in your hot water cistern.

This type of cistern works by harnessing what heat is available from the sun before ‘topping up’ using your existing boiler. It should qualify for the Renewable Heat Incentive scheme, which will help you recoup the initial expense of installing it.

Use your existing solar panels

If you already have a solar panel system to provide your home with free electricity, then a solar hot water system isn’t a practical add-on. If you have an existing hot water cylinder with electric immersion heater, however, then you can divert any excess energy your panels produce into heating your hot water using what’s known as a solar immersion heater.

It’s not the most efficient use of your electricity, and if you’re currently earning money from your panels by exporting that excess back to the grid, you may need to work out whether the lost income is outweighed by the reduced costs of heating your water (it’s estimated a solar immersion heater can provide the equivalent of eight-to-nine months of free hot water each year). Units can be bought for as little as £230, but you’ll need to employ the services of a qualified electrician to fit them. Expect to recoup the outlay in 2-5 years depending on how much you pay.

Hot water: FAQs

How long should I heat my water for?

If you have a hot water cylinder, then hot water stays hot for hours if not days if it isn’t used. Invest in a timer to heat the water only when it’s most frequently used – typically in the morning and evening when people are most likely to take baths or showers, and you need to wash up.

Could I leave my hot water on permanently?

This is wasteful, given that the water will stay hot for hours if it’s not being used.

How long does water stay hot in a tank?

This depends on the type and age of your cylinder or cistern, and how well-insulated it is. Older models won’t hold heat for more than a day at best, while newer models can hold it for up to 48 hours.

Do I need a combi boiler when I only need hot water?

A combi boiler is used both to heat water and your home. They’re energy-efficient because although they’re on all the time, they only produce hot water when it’s needed, thus helping to reduce your bills. They’re also perfect for smaller homes, as you no longer need to find space for a separate hot water tank.

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Published on Wed 31 Mar 2021 04.13 GMT