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Energy-efficient hot water

Energy-efficient hot water

Hot water accounts for around 10% of the average energy bill. It's not something most of us would want to do without, so use this guide to find energy-efficient ways of getting your hot water, and tips to help you use less of it.

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What methods of heating water are available and what do they cost?

Although there are different ways of heating water, the main supply is usually heated by the central heating system - either 'stored' within a cistern (tank) or available 'on demand' if you have a combi boiler.

Generally speaking, modern combi boilers are more energy-efficient than a hot water heater system with a tank or cistern.

There are several other ways of water heating, including solar hot water systems, immersion heaters, electric water heaters, electric showers and, of course, kettles.

To give you a rough idea of prices, an electric shower can cost between £50, for a simple model, all the way up to £700. Solar hot water systems are much more expensive and could set you back up to £5000. A standard immersion heater will cost roughly £150 to purchase and install (£120 for the installation process and around £30 to buy the actual immersion heater).

How much of my energy consumption is used for heating my water?

It's difficult to be exact about the energy that is used for heating water because it's hard to measure, and difficult to separate out from the energy your boiler uses for heating.

However, in a typical home the cost of heating water is likely to exceed 10% of the energy bill or approximately a quarter of the fuel used by the boiler. This may seem high, but remember you need hot water all year round, whereas heating is seasonal.

The true cost of hot water should also take account of the cost of the water supply itself, which in some cases can be as high as the cost of heating it.

Some people can save by switching to a water meter – as a rough guide, if you have more bedrooms than you have people living in your home a meter is worth looking into.

Water heater

What types of shower are there?

We're often told to take a shower rather than have a bath to save energy and water. But what types of shower are there, and are they all really better than taking a bath?

Showers fall into three broad types:

  • Electric showers are widespread and use electricity to instantly heat water as it passes through the unit at mains pressure.
  • Mixer showers draw on both hot and cold water supplies and mix them together.
  • Power showers generally use stored hot water, which is then mixed with cold water and pumped out using an electrically powered pump.

What type of shower is the most cost-effective?

Given the cost of gas is only about 40% that of electricity, in theory, a mixer or power shower might be more cost efficient than an electric shower. However, electric showers usually use less water and therefore require less energy, so a lot depends on how long you are showering for.

In addition, electric showers are efficient due to the fact that the water is heated at the point of use, whereas with power and mixer showers heat is lost through the cistern and pipes before it even reaches the shower.

Power showers also use so much water that the traditional advice of taking a shower rather than a bath to save energy and water may not apply. Water costs will also be higher for power and mixer showers if you are on a water meter.

Hot water

What can I do to lower my water heating costs?

Here are some straightforward ways to lower your water heating costs:

  1. Choose carefully how you heat water.
  2. Be sensible about when you heat hot water.
  3. Use less hot water.
  4. Heat your hot water to a lower temperature.
  5. Don't let hot water cool down before you have used it.

Top tips to save on your water heating that are FREE

  • Turn down the thermostat on your cistern to 60-65°C.

  • If you have an old central heating system, the temperature of the hot water will be determined by the internal circulatory system, as set on the boiler, so turn that down.

  • Use a kettle for the times you need very hot water.

  • Check the timings and other controls on your boiler for your water heating, which on an older boiler will often be integrated with the timings of your central heating.

    You may be able to reduce the length of time that the water heating is turned on, especially in the summer.

  • Check to see if your power shower pump has flow controls. If it does, you should be able to reduce the flow.

  • With any type of shower, check to see if you can adjust the shower head spray pattern - you may find that you can reduce the flow of water.

  • If you wash up by hand, don't rinse the dishes under running hot or cold water. Instead, use a separate bowl.

  • If you have an older boiler it's a good idea to use an immersion heater in the summer.

Top tips to save on your water heating, for just a small investment

  • If you have an old cistern (tank) that isn't insulated, then fit a tank jacket.

    This should pay for itself in just a few months and you can add to the insulation effect by storing bedding, pillows and towels around the cistern.

  • Where they're accessible, insulate the 'downpipes' - these are the pipes that lead from the cistern to the taps.

  • If you have a mixer or power shower, fit a shower head flow regulator or a shower head that aerates the flow. Both reduce the flow of water, cutting water and energy use.

  • If your hot water is solely or often heated using an immersion heater and you don't already have a timer on it, it's a good idea to fit one.

    This is particularly useful if you have an Economy 7 supply, as it means you will be able to heat your water using overnight cheap electricity.

  • Fix dripping taps. If you don't feel confident putting new washers in your taps, you could ask your plumber to do it.

  • Buy a shower timer to check how long you're really spending in the shower.

  • Make sure your shower is in good condition, including the shower head, the hose and the wall mounting.

    Replace parts if necessary and de-scale your shower head regularly if you live in a hard water area, otherwise scale build up will affect the water flow.

Top tips to save on your water heating, moderate to high investment

  • If your hot water cistern is very old, consider replacing it with a modern insulated one.

    Water can stay warm for up to two days and they perform much better even compared to an old-fashioned tank with a jacket on it.

  • If you're thinking of installing a solar hot water system in the future, it may be worth installing the larger-sized tank with the required two heat inputs - one for the central heating and one for the solar panel.

  • If your boiler is over fifteen years old, it could be time to replace it. A modern combi-boiler, which provides instant hot water, is generally considered to be more energy efficient than a 'stored' hot water system.

  • You could install solar water heating (SWH), also known as solar hot water (SHW).

    This is an expensive measure, but the introduction of the Renewable Heat Incentive (RHI) by the government will help you to recoup some of the upfront costs over time.

How does solar water heating work and should I install it?

Solar water heating works by circulating a liquid through a panel on an approximately south facing roof, or occasionally a wall or some kind of ground-mounted system. There are two types of panel -- a 'flat panel' and the more expensive, but more efficient, 'evacuated tube'.

The liquid is warmed by sunlight — even in cloudy weather — and this liquid is circulated through the hot water cistern, transferring its warmth to the water there.

A solar system can only work with a larger cistern with two heat inputs — one from the boiler and one from the solar panel.

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