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Underfloor heating explained

Water underfloor heating

By Liz Ransome-Croker

Article 2 of 4

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Water underfloor heating

If you're considering water underfloor heating, make sure you know how it works, how much it costs and what the installation process involves.

A water underfloor heating system can be a great way to warm floors on a winter's day, and can sit beneath most types of flooring. But compared with electric underfloor heating, water systems are more complicated to install and a lot more expensive to buy.

How does a water underfloor heating system work?

With a water-based underfloor heating system, a series of pipes connected to your boiler circulate warm water throughout the floor to heat the space, similar to radiators. 

Alternatively, you can connect the underfloor water pipes to a solar water-heating system, air-source or ground-source heat pump.

The pipes will be connected to your heat source using a manifold (essentially a central system allowing all the pipes to work together) – see the image below for an example of what they look like. 

The bigger the system, the more pipes it will have and the more complex the manifold will be. The system will also be fitted to a thermostat (or thermostats, if you're having more than one zone) so that you can regulate the temperature.

Any plumbing work will need to be carried out by a professional. You can use Which? Trusted Traders to find one in your area. All traders affiliated to Which? have been through extensive background checks.

What temperature does water underfloor heating need to be?

Water underfloor heating typically runs at a lower water temperature than radiators. It's usually between 27°C and 31°C, but the exact temperature will be determined by the flooring used to cover it. The harder it is for heat to get through the floor, the warmer the water running under it will need to be. 

If the system is installed in screed (which is used to keep the system in place and make the surface even), the water temperature may need to be higher. But this will again depend on the floor type and thickness of screed. 

Most water underfloor heating systems will be installed with a mixing valve, which can reduce the water temperature to the desired setting. It also means you can keep the boiler running at the temperature you want for the rest of the house.

Water underfloor heating installation 

After a professional has checked your boiler to ensure it can support the system, and the design and layout for each room and zone has been completed, pipes can be laid and fixed, usually using fixing clips. 

Pipes will then need to be connected to a manifold, the heating system and a thermostat to control the heat for that room. This should always be done by a qualified plumber or electrician, who should test the system at this point. 

Once the pipes are down, insulating screed (a material usually made of cement and sand) is put on top to hold the pipes in place, insulate the system further and to level out the floor. Some installers don't do this – you may need to get it done separately by a builder. This may be someone working for the installation company, or you may need to get outside help. 

If your installer can't complete the entire process, ask if they can recommend other builders, and ideally get them to co-ordinate their work. 

Unlike using ready-to-roll electric underfloor mats – which confident DIYers could lay themselves – a water underfloor system should ideally be installed by a professional. This is because it's a more complex process, with plumbing connections and tests that need to be carried out.

The floor must be properly prepared and insulated to make the system work efficiently. There needs to be enough space to accommodate this and the piping, so you might have to raise the finished floor level. Because of this, it's easier to install water underfloor heating in a new build, as these adjustments can be taken into consideration from the start.

However, there are now a lot of low-profile floor systems that you can have installed in an existing room without raising the floor considerably or significantly disturbing fittings. 

Find out more about this and the other considerations you'll need to make before getting underfloor heating by visiting our underfloor heating costs and pros and cons pages.

What type of boiler do you need for underfloor heating? 

Water systems will work with any type of boiler, including condensing, wood-fired or vented. In fact, they will work with any type of heat source, such as a heat pump. 

The system will be connected to the heating via a manifold. Electric underfloor heating systems, on the other hand, only need to be connected to your electrical supply.

When we called installers across the UK and water underfloor heating, some mentioned needing to get a new, more efficient central heating system. If this is suggested to you, make sure you get a few opinions before going ahead. 

If you're thinking about getting a new or different central heating system, it might be worth considering a ground- or air-source heat pump, as these run at lower temperatures (50°) than boilers, so are ideal for underfloor heating.

How much does water underfloor heating cost to install and run?

Water underfloor heating is typically more energy efficient than radiators, and is therefore less expensive to run. This is because the heat emitted from an underfloor system is more evenly distributed than heat from a single radiator, so the system can use water at a lower temperature. 

But this isn't always a given, nor is how much you might save on your energy bills over time. It will also depend on a lot of other factors, including:

  • how energy efficient your home is
  • the size of system and room
  • how you use your heating.

See our guide to underfloor heating costs to find out the latest prices from RICS.

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