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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 more complicated to install, and a lot more expensive to buy.

When we asked owners of underfloor heating about which type they have in their home, 35% said they have a water system compared with 65% for electric*. But water heating does have benefits, such as being generally more efficient and cheaper to run.

To help you make the decision on which type to choose, or, in fact, whether to get underfloor heating at all, we've spoken to hundreds of Which? members who own it to find out about their experiences. 

We've also spoken to industry experts from The Underfloor Heating Store, Warmup Plc and Polypipe to get insider information. Head to our underfloor heating pros and cons page for the benefits and drawbacks of both systems, but keep reading for the answers to commonly asked questions about water underfloor heating.

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. 

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 – 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 to radiators. It's usually between 27-31°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 amount 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.

Visit our page on underfloor heating costs and installation for more on what other factors could affect the temperature your system runs at, and what the best types of floor covering are.

Where can water underfloor heating be installed? 

You can have a water system installed pretty much anywhere. When we asked water owners of underfloor heating where they had it installed in their home*: 

  • 75% had it in their kitchen
  • 67% had it in their living room 
  • 56% had it in their hallway
  • 42% had it in their bathroom.

The highest percentage of people (25%) had it installed in two rooms, while for electric underfloor heating, most people (66%) had it installed in just one. This is probably because water systems can be more efficient to run, and can do so at lower temperatures, so they're better suited to bigger rooms and use in multiple places.

For those with an electric system, most had it fitted in their bathroom (a typically smaller room), followed by the kitchen. 

What happens during a water underfloor heating installation?

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.

86% of water underfloor heating owners we asked had it installed by a company, supplier or builder. Just four people installed it themselves.

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 elevate the 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 possibly at all, or disturbing fittings. 

86%of people used an expert to fit their water underfloor heating

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 installation and pros and cons pages.

You can find recommended heating engineers or underfloor heating specialists in your area using Which? Trusted Traders. They'll be able to advise you on the best type of underfloor heating for your room size and shape, as well as how it will affect your floor.

They will also need to test your boiler to check it can support the system. Water underfloor heating can work with all types of boilers, but an older system might mean you need to run your water system at higher temperatures.

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

Water underfloor heating is typically more energy efficient than radiators, and 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.

A water underfloor system is more expensive to fit than an electric one, in part because it's more complicated to install. The price can also be affected by a number of other factors, such as whether the room you want it on a floor that's badly insulated or far away from your heating system. 

We can give you details on how various factors can affect the price, based on speaking to dozens of installers across the UK. We've also asked underfloor heating owners whether they think it has saved them money on their energy bills. See our guide to underfloor heating costs and installation to find out more.

(*In November 2017 we asked 104 Which? members with underfloor heating about their experiences with it in the last five years.)

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