Exclusive app offer: free delivery on orders over £200*Terms & conditions apply
Who are we
Energy-efficient water heaters: what are the options?

Energy-efficient water heaters: what are the options?

Julie, Interior Designer, Manchester

Guide written by:

Julie, Interior Designer, Manchester

41 guides

An energy efficient home must be able to provide hot water without consuming too much energy. But when it comes to choosing a water heating system, there is a lot of choice out there including solar water heaters, thermodynamic water heaters, biomass boilers and hydro stoves. Read on to find out more.

Water heating systems are often overlooked in favour of insulation or heating systems when it comes to improving energy efficiency in the home. Nonetheless, hot water production represents a substantial portion of your overall energy consumption. According to UK government estimates, water heating accounts for approximately 20% of a home's total energy use.

Nowadays, there are several energy-efficient ways to heat water including systems powered by renewable energy. Switching to an efficient low carbon system can seriously lower your carbon footprint and reduce your energy use by about 50%.

There are three different types of energy-efficient water heaters for domestic use:

  • Solar water heaters which take heat from the sun to heat water. Economical and eco-friendly, these systems come in different types to meet various budget and installation requirements.
  • Thermodynamic water heaters are designed to work like aerothermal heat pumps. Easy to use and programmable, you'll make your investment back on these heaters in just a few years.
  • A low carbon heating and water heating system (hydro stoves, etc.): these systems are used to provide heating and hot water. However, you will still need a secondary water heating system when the heating is switched off, which does lower performance.
A thermodynamic water heater will pay for itself in about five years on average while a solar water heater can provide you with up to 60 to 70% of your hot water needs.

Solar water heaters are made up of solar collectors and a water storage tank. The size of the solar collectors – which may be solar panels or solar tubes – and the volume of the tank dictate the amount of hot water you can produce. On average, this type of system can be expected to cover about 50 to 70% of your overall needs which will translate directly to your energy bills!

Different types of solar water heaters

There are a few types of solar water heaters. Your decision should be made according to your needs and budget.

  • In compact solar water heaters, the solar collector and storage tank form a single unit which is installed in one spot, either on the ground or on a roof. These solar water heaters are the easiest and most cost-effective type to install since they do not require the use of a pump; the water is simply heated by the sun and becomes less dense which allows it to rise in the storage tank. However, as the storage tank is kept outdoors, it is more difficult to maintain water temperatures. Furthermore, this type of storage tank can be a bit of an eyesore.
  • In thermosyphon systems the storage tank is usually placed above the solar collectors (generally on top of a roof). This means that the hot water naturally rises in the tank while the heavier cold water drops. This is what is known as a passive solar heating system.
  • An active solar heating system is equipped with a pump which means you can install the storage tank wherever you like. Heat transfer fluid is used to transport the heat collected via the solar collectors and heat exchanger towards the storage tank. A second circuit transports the hot water to the home. These closed circuit systems are the most common but also the most expensive type of solar water heater. They are also the most complex to install. In these highly efficient systems, the heat transfer fluid is usually mixed with anti-freeze. They also generally feature a controller which is triggered in certain conditions.

Solar water heaters can also work using a drainback system. In this case, the solar panel will be installed above the tank. When the sun stops heating the solar panels or tubes, circulation stops and the circuit is automatically drained.

Thermodynamic water heaters use heat from the air to warm up water which can save you up to 70% on your water heating bill. And don't worry about getting caught out if your hot water needs suddenly rise or if outdoor temperatures get too low as these water heaters are also equipped with a heating element which will take over.

Be sure to pick the right tank volume to ensure you don't have to rely on the element too often since this will end up making your system less eco-friendly and less cost-effective.

How does a thermodynamic water heater work?

A thermodynamic water heater features an aerothermal heat pump and a storage tank. The heat pump collects naturally occuring heat from the air and uses it to heat up liquid refrigerant. This liquid turns into a gas as it is heated before it is sent to a compressor. The compressor then increases the pressure and temperature of the gas, and transfers the heat to the storage tank via a heat exchanger. As it cools down, it turns back into a liquid and the whole process starts again.

Choosing the right spot for a thermodynamic water heater

Thermodynamic water heaters are designed to extract heat from indoor or outdoor air.

  • If used to extract heat from indoor air, the thermodynamic water heater must be installed in a room located far away from primary living spaces with a volume of 20 m3 (or a surface area of 10 m2). The room must not be heated but, at the same time, mustn't be allowed to drop below 5°C.
  • If used to extract heat from outdoor air, the thermodynamic water heater can either rely on a ducting system or it can be split meaning the storage tank is set up indoors while the heat pump installed outside. Thermodynamic water heaters offer a practical solution as part of a wider renovation project or if you have an unheated room such as a garage or basement. They are, however, slightly less efficient in cold weather.

Some cost-effective and environmentally friendly heating systems can also be used to heat water. In this scenario, hot water can be produced by a biomass boiler, wood burning stove, or even an energy-efficient boiler.

Biomass heating and water heating

Biomass boilers provide not just an eco-friendly and efficient way to heat homes – they can also be used to produce hot water. While theoretically, a biomass boiler can provide instantaneous hot water, this solution is rarely used as it is not economical and will only meet minimal hot water requirements.

With this in mind, wood burning boilers are often paired with a storage water heater which is used to store any hot water produced. A wood pellet boiler offers greater energy efficiency and independence.

You do need a lot of space when installing a biomass heating and water heating system and this must be accounted for before carrying out renovation work. You'll also need enough space to store wood pellets or logs.

Wood burning stoves and water heating

Just like with a biomass boiler, it is possible to use a log burning or pellet stove to make hot water. These appliances are called hydro stoves or thermo stoves, and are linked to a buffer tank which is used to produce hot water.

In the same way as a biomass boiler, this process is only really worthwhile when your heating system is on over the winter months. Bear in mind that the thermal performance of your heating system may be reduced as the water is heated.

You will have to find another solution for hot water over the summer months or whenever your central heating system isn't running.

Guide written by:

Julie, Interior Designer, Manchester, 41 guides

Julie, Interior Designer, Manchester

After years of DIY, renovation and designing, I decided to turn my passion into a career. Starting in 2006, in the South-West, I helped people with renovation or construction projects. My expertise and curiosity led me to look further into innovative ideas for myself and my clients. Indeed, to live your passion is also to transform the space you live in and the objects you use daily. My family love my creations and ideas that I bring into their lives! My favourite thing to do: use colour to brighten up interior space. But also tips to hide away clutter. Your home is just never big enough, is it? It is therefore a great pleasure to share my tips with you, so that you also can take as much pleasure as I do when starting up your next project!  

  • Millions of products

  • Delivery to your home or click & collect

  • Hundreds of dedicated experts online