Using hot water efficiently

The cost of heating water makes up a high percentage of your overall energy bill. Here’s a look at how to save both money and energy.

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Person regulating hot water temperature in shower

In this guide:

  • What’s the cheapest way to heat water in my home?

  • Hot water and heating costs: types of showers

  • Simple ways to lower hot water costs

  • Tools to save on your hot water

  • When should I replace my hot water system?

  • How does solar hot water work?

  • Frequently asked questions about using hot water

What’s the cheapest way to heat water in my home?

There are several different ways to heat water in the home. Your main water supply will usually be heated by a central heating system, either provided on demand by a combi boiler or stored inside a cistern tank. 

Combi boilers are usually the cheapest way to heat water for your home, particularly newer models that have been designed to be more energy-efficient than tanks or cisterns. 

Immersion heaters are another option for providing hot water. These are electric water heaters contained inside an insulated hot water cylinder. An immersion heater functions a bit like a kettle, using an electric element to heat the surrounding water. It connects to the electric mains, which means you can switch them on and off to save money and energy. 

Additional options include electric showers and solar hot water systems. These vary widely in price, with electric showers at the lower end costing around £500, and solar hot water systems at the other, costing closer to £5,000. 

Efficiency is more important to consider than this upfront cost, because hot water makes up such a high percentage of your energy bill. In the typical UK home, heating water usually comprises over 10% of the overall energy costs. While heating is seasonal, you need hot water throughout the year. 

When calculating the cost of hot water, you’ll also need to think about your water consumption. The supply of water can cost as much as heating the water in some cases. Switching to a water meter might save you money if you have a larger household, so that you can track your usage and identify potential savings. 

Hot water and heating costs: types of showers

Most of us take showers more frequently than baths. But how do they measure up to baths in terms of hot water use? This will depend on the type of shower. While an eight-minute shower uses 62 litres of hot water on average, less than the 80 litres needed for an average bath, some types of power showers use up to 136 litres.

Updated 2 December 2020
Type of showerDescription
Electric This popular type of household shower uses electricity to heat the water. Water is instantly heated as it passes through the mains unit.
Power These use stored hot water, mixed together with cold water and pumped out with an electric device.
Mixer This type of shower is less common, drawing from both hot and cold water supplies in the home and blending them together.

Although gas costs less than electricity, electric showers are the most efficient out of the three options above. They use less water overall, and so require less energy to heat. Electric showers are also heated at the point of use for an instant flow of consistently hot water. In contrast, power and mixer showers have to be piped in from a cistern which takes more energy overall. 

Keep in mind that the cost and energy use of your shower can vary quite significantly. If you enjoy long, leisurely showers you’ll be using more hot water than someone who’s in and out with a quick shampoo. One way to significantly reduce costs is to only switch the shower on to rinse – by switching it off while you wash, you can reduce your consumption of both water and energy.

Simple ways to lower hot water costs

Simply being more aware of the hot water you’re using each day can help you reduce your hot water costs. A water meter can help with this, showing you where and when you’re heating water so that you can use less of it. In addition to this, here are a few other ways to trim your hot water bills. 

  • Check your boiler’s timings and other settings to make sure water heating is timed to when your household needs it. 

  • Don’t keep the hot water running when you’re doing the washing up. Instead, fill the basin once and rinse separately. 

  • If you have a water cistern, turn the thermostat down slightly to fall between 60-65°C.

  • Adjust your shower’s spray pattern and flow setting to reduce the amount of hot water you’re using. 

Tools to save on your hot water

In addition to the no-cost tips mentioned above, there are several inexpensive tools or gadgets you can use to reduce your water costs.

  • Fit an insulating tank jacket to your cistern. This helps lock in warmth and keeps water hot throughout the day while using less energy. If you store pillows, towels and blankets around the cistern, you’ll insulate it further. 

  • Fit a shower head flow regulator to your shower, particularly if you have a mixer or power shower. This reduces the flow, cutting your energy use. 

  • Timers can come in quite handy when you’re trying to cut back on hot water use. For example, you could put a timer on your immersion heater. You can set it to heat water overnight if you have an Economy 7 supply with cheaper rates. Time yourself in the shower as well so that you don’t lose track of time. 

  • If you live in an area with hard water, descale your shower head to prevent any build-up that forces it to work harder than necessary. 

When should I replace my hot water system?

Modern boilers and cisterns are far more efficient than older designs. If your hot water cistern is over a decade old, it might be worth replacing it with a modern, well-insulated model. These keep water warm for up to two days. 

The average lifespan of a boiler is about fifteen years. If yours is past this age, consider replacing it with a modern combi boiler for instant hot water on demand. 

How does solar hot water work?

If you’re looking for a greener way to heat your water, you might be considering solar water heating. This type of system uses solar panels mounted either on your roof, wall or ground. Some are flat in shape, while others come in a more efficient tubular shape. In either case, a liquid is passed through the panel and warmed by sunlight, before transferring into your water cistern to transfer heat. To work, the system uses heat inputs both from the solar panel and your boiler. 

Although it is expensive to install, this type of system can reduce your overall energy costs in the long run. You might also qualify for the Renewable Heat Incentive, which could help you get some of that money back. 

What’s a solar immersion heater?

Most people with solar panels use them to generate electricity. Solar immersion heaters are special devices that can work in conjunction with solar panels, an existing hot water tank and electric immersion heater. They basically divert excess electricity into the immersion heater to heat up your water. It’s not particularly efficient, and will reduce any money you might earn from exporting electricity to the grid, but it’s capable of delivering free hot water for the equivalent of up to nine months of the year, reducing your energy bills accordingly. They cost as little as £230 plus fitting, and you can recoup your initial outlay in just a few years.

Frequently asked questions about using hot water

How long should hot water be on for?

This will depend on your household’s typical usage patterns. For example, you could use a timer to heat your water during the hours that your family typically needs it for baths and showers. Most modern appliances like washing machines and dishwashers heat their own water, so don’t need a constant supply. 

Is it cheaper to leave hot water on all the time?

This is a common misconception that in most cases isn’t true. You don’t need to heat your water all the time, provided you have a good insulating jacket to keep the water hot in your immersion heater or boiler. 

How long will a water tank stay hot?

It depends on the type of water tank you have, and how well it’s insulated. A modern, well-insulated cistern can keep water warm for up to two days, but older models might only keep the water hot for a day or less. 

Can I use a combi boiler for hot water only?

A combi boiler is used both for heating and hot water. Combi boilers are energy-efficient because they only produce hot water when you need it. You won’t be heating up water when it’s not needed, which is a way to lower overall bills. They also do away with the need for a separate hot water tank, which can save both space and energy.

Last updated: 2 December 2020