Water underfloor heating

If you're aiming for a cosy home with low running costs and you're already taking on building works, water underfloor heating could be for you.

Although it can be expensive and difficult to install, it's typically inexpensive to run and an effective (and powerful) way to heat your home. 

It's a great option if you are already renovating your home or you're specifying a new build. It can also be worth the spend if you need to heat a large area, like a kitchen diner. Electric underfloor heating is less disruptive to lay but more expensive to run, so it's not advised for heating large, open parts of your home.

Here's a rundown of how water underfloor heating systems work and what's involved in the installation process. 

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How does water underfloor heating work?

In a water-based underfloor heating system, a series of pipes circulates warm water under the floor to heat the space. These are typically connected to your boiler. 

However, as a more sustainable option, you can also connect them to a solar water heating system or an air-source or ground-source heat pump. 

You need something called a manifold to connect the underfloor water pipes to your heat source. 

An underfloor heating manifold consists of two rows of taps, which allow the heated water to circulate from the boiler (or other heating source) through the underfloor circuits. 

The system will also be fitted to a thermostat (or thermostats, if you have underfloor heating in more than one room or area) so that you can regulate the temperature of your floor.

Underfloor heating water temperature

Because it covers a larger area, water underfloor heating typically runs at a lower water temperature than radiators (as low as 35°C, compared with 55-65°C or even higher for radiators). This makes it an efficient, cost-effective heating option as compared to radiators.

The exact water temperature needed for underfloor heating will be determined in part 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. 

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

Discover more about electric underfloor heating in our guide to wet systems

What do Which? readers think about their water underfloor heating? 

It can be difficult to know whether the benefits of water underfloor heating are worth the investment until you've already made the decision. 

So, in May 2024, we asked 41 Which? members who've had water underfloor heating installed whether they think it was a worthwhile investment. 

If you're a Which? member, you can log in to unlock our insights from members who already own underfloor heating.

Not yet a member? Join Which? today to see our advice, as well as exclusive underfloor heating cost data from the Royal Institution of Chartered Surveyors in our guide to underfloor heating costs and installation.

You'll also unlock thousands of product reviews, from boilers to vacuum cleaners. 

Read more our readers' experiences in our guide to the pros and cons of underfloor heating 

Water underfloor heating cost

Water underfloor heating is generally more expensive to install than electric underfloor heating because it is more complex. However, as it runs off the boiler (generally using gas), it is typically quite cost-effective to use. 

Based on estimates from underfloor heating manufacturers, we've calculated that the annual running costs for water underfloor heating for a 10m2 room can be as low as £45. 

This is much cheaper than electric heating, and it is likely to be cheaper than using radiators. 

This is because water underfloor heating is typically around 25% more efficient than radiators. As the heat emitted from an underfloor system is more evenly distributed than heat from a single radiator, the system can use water at a lower temperature. 

Actual running costs for underfloor heating systems will vary considerably, as they are impacted by factors such as:

• Your home's insulation
• The size of the area to be heated
• How long the system runs for
• Your gas tariff

Check our guide to underfloor heating costs and installation to find out the typical prices for different scenarios based on information from the Royal Institute of Chartered Surveyors (RICS).

Water underfloor heating installation

While it is sometimes possible for confident DIYers to lay electric underfloor heating themselves, water underfloor heating is best installed by a professional. This is because it's a more complex process, with plumbing connections and tests that need to be carried out.

If your home is suitable for water underfloor heating, the professional will first plan out the design and layout for the system. The pipes can then be laid and fixed.

Next, the pipes will need to be connected to a manifold, the heating system and a thermostat to control the heat for that room. Even if you've laid the pipes yourself, this part should always be done by a qualified plumber or electrician who can test the system.

Once the pipes are down and the system set up, insulating screed is usually put on top to hold the pipes in place, insulate the system further and to level out the floor. Some underfloor heating installers don't do this part – you may need to get it done separately by a builder. 

If your installer can't complete the entire process, you can find a builder using Which? Trusted Traders. Ideally, get the installer and builder to co-ordinate their work so you're not left with an unfinished floor for too long. 

To learn more about how much owners report spending on installing and running their heating, see our guide to underfloor heating costs and installation

Where can water underfloor heating be installed?

In principle, water underfloor heating can be installed in pretty much any room, as long as you have the appropriate water pipework infrastructure in place and a suitable heat source (a boiler or heat pump, for example). 

Because water underfloor heating is so powerful, and it runs off gas (which is cheaper than electricity), it is a good option if you want to heat multiple rooms. 

Although some of our readers had it installed in one room (32%), the majority had it installed in four or more (54%). 

Bear in mind that water underfloor heating pipes take up more space than electric underfloor heating, and the floor must also be properly prepared and insulated to make the system work efficiently. This might mean having to raise the finished floor level. 

There are low-profile floor systems available that you can have installed in an existing room without raising the floor considerably or significantly disturbing existing fittings, but you will need to consult with a professional to see if these systems will work for you. 

Water underfloor heating thickness

The thickness of your heating will depend on the system that you choose, as they require different layers of material to run safely and effectively.

Water systems are generally bulkier than electric systems and can be around 130mm thick - thicker if retrofitted. 

Does underfloor heating need a special type of boiler?

No. Underfloor heating works perfectly well with the types of boilers that most people already have in their homes, including combi gas boilers, traditional tank-based gas boilers and oil boilers. 

However, your existing boiler may need some adjustments to work effectively with the underfloor heating system and, in a few cases, may not be suitable. 

You should always get a professional to assess your heating system's suitability before committing to getting water underfloor heating installed.