Water underfloor heating

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. 

Water - or wet - underfloor heating tends to be less popular than electric underfloor heating, because it's more complicated to install and up-front costs can be much higher. However, running costs to heat the same sized room are typically lower than an electric equivalent. 

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

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How do water underfloor heating systems work?

With a water-based underfloor heating system, a series of pipes circulates warm water under the floor to heat the space. 

These pipes are typically connected to your boiler, but 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 heating pipes to the heat source.  

What is an underfloor heating manifold and do I need one?

A manifold is at the heart of your underfloor heating system, connecting the underfloor water pipes to your heat source and allowing them to work together. 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 image above shows an example of what a manifold looks 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 have underfloor heating in more than one room or area) so that you can regulate the temperature.

What temperature does water underfloor heating need to be?

Water underfloor heating typically runs at a lower water temperature than radiators – as low as 35°C, compared with 55-65°C for radiators, according to energy manufacturing trade association BEAMA. 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. 

If the system is installed in screed (a material usually made of cement and sand 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 adjust the water temperature to the desired setting to keep the area it's heating cozy. It also means you can keep the boiler running at the temperature you want for the rest of the house.

Where can water underfloor heating be installed?

When we asked Which? members with underfloor heating about the type of system they had, 38%* had water underfloor heating. The kitchen was the most popular room to have water underfloor heating, followed by the living room. 

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). In practice, it's not quite that simple. 

For example, 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. Because of this, it's easier to install water underfloor heating in a new build property, as these adjustments can be taken into consideration from the start.

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

If you're considering installing water underfloor heating, the first step is to ask for an assessment of whether your home is suitable, including whether your boiler can support the system. Most existing boilers should work, but may need some adjustments. 

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How do you install water underfloor heating? 

While it is sometimes possible for confident DIYers to lay electric underfloor heating themselves (though it will need to be connected by a qualified electrician), 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 each part of your home that will have underfloor heating installed. The pipes can then be laid and fixed, usually using fixing clips. 

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 should test the system at this point. 

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. This could be someone else working for the installation company, or you may need to get outside help. 

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. 

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

Does underfloor heating need a special type of boiler?

No. Underfloor heating will work perfectly well with the types of boiler that most people already have in their home, including combi gas boilers, traditional tank-based gas boilers, or 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. 

That said, if your heart is set on water underfloor heating but an installer suggests you need a new boiler or heating system for it to work, it's worth getting a second opinion before shelling out on upgrading your entire system. 

Is water underfloor heating compatible with heat pumps?

While water underfloor heating can work effectively with boilers (either gas or electric), it's also compatible with heat pumps, and can work very efficiently in tandem. 

Heat pumps run at lower temperatures (50°C) than boilers. This means they can work well with underfloor heating systems, which run at lower temperatures than radiators and so won't require the higher temperatures offered by boilers. 

Head over to our full guides to find out more about air source and ground source heat pumps.

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

To find out how much it might cost to install both water and electric underfloor heating, head over to our guide to Underfloor heating costs and installation, where we've worked with the Royal Institute of Chartered Surveyors to provide typical costs for certain scenarios. 

Running costs are trickier to calculate, as there are many variables. We do know, though, that water underfloor heating is typically much cheaper to run than electric underfloor heating, on a like-for-like basis. That's in large part down to the fact that electricity costs significantly more per unit of energy than gas, which is usually used to heat water-based systems. 

Water underfloor heating is also typically more energy-efficient than radiators – typically around 25% more efficient. This will make water underfloor heating 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.

To get a quote for water underfloor heating, use our Which? Trusted Traders to find local underfloor heating installers. All Trusted Traders affiliated to Which? have been through extensive background checks.

*In December 2021 we asked 119 Which? members who had fitted underfloor heating in the past five years about their experiences.