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Underfloor Heating: Advice on Specifying a New System

underfloor heating pipes laid before screed
(Image credit: Nu Heat)

You might think of underfloor heating as a bit of a luxury — simply offering up warm floors underfoot. However, it's much more practical than that. It's an effective method of space heating that eliminates cold spots and is more energy efficient. 

Installation of underfloor heating (UFH) is a big job, but one of the benefits of choosing it when building a self build or extension is that you can factor it into your build, making the job much easier and less disruptive than trying to retrofit it into an existing property. 

Our beginner's guide to underfloor heating focuses on wet UFH, which uses your home's central heating system, and looks in depth at the pros and cons of these systems, how they're installed, what you'll need to factor into your build and, vitally, how much you can expect to pay. 

What is Underfloor Heating? 

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Underfloor heating involves the installation of a system (of either pipes or wires) into the floor. The floor, in essence, becomes the entire radiator, heating the room. 

It warms the room from the ground up and offers improved comfort levels as well as less demand on your boiler than a traditional radiator system. This is due to underfloor heating having a lower operating temperature (around 40°C) than a radiator system, which normally operates at around 65°C.

Underfloor heating works really well with renewable technology such as heat pumps, which have a low flow rate.

an underfloor heating plan with zones

This underfloor heating layout plan from Nu Heat shows the different zones spread across a ground floor level install.  (Image credit: Nu Heat)

What Type of Underfloor Heating is Best?

There are two main types of underfloor heating:

In basic terms, a wet underfloor heating system features pipes, filled by warm water and powered by a boiler or heat pump, concealed within the floor, and typically embedded within a floor screed

This is the best type of underfloor heating for those building from scratch and/or planning a whole-house system.

Electric underfloor heating is often cheaper and easier to install than wet underfloor heating. However, the running costs can be three times higher.

underfloor heating being installed in a new build

(Image credit: JK Floorheating)

It is often a good idea to install electric underfloor heating in a small, single area like a bathroom or en suite, where it may be difficult to install wet underfloor heating.

One of the most common — and worst — uses for electric underfloor heating is in a conservatory. Typically these areas need a lot of heat and are used for relatively long periods of the day (compared to a bathroom).

Then running cost becomes the key issue and the extra trouble and expense of a wet system is well worthwhile.

If you are opting for a whole-house underfloor heating system, there will be separate pipes running into each room. This allows you to control when those rooms or ‘zones’ are heated and for how long, preventing you from having to heat unoccupied spaces.

What are the Advantages of Underfloor Heating?

  • Reduces cold spots across large areas. 
  • Run at a lower temperature than radiators, meaning UFH is more energy efficient. 
  • Compatible with many types of flooring. 
  • Removes need for space-stealing radiators.
  • Safer for children, and better for indoor air quality. 

What are the Disadvantages of Underfloor Heating?

  • Underfloor heating is more expensive to install than a comparable radiator system — it typically costs 20% to 50% more.
  • Installation time can be longer, especially with wet UFH. Even electric underfloor heating may require work to self level before installation. 
  • When retrofitting underfloor heating, changes to floor height will need to be considered. This may require extra work in digging out the floor for a level profile. 

Can I Install Underfloor Heating into my Existing Home? 

While it's best to install underfloor heating at the time of building, you can install it in your existing home, but you will need to opt for a low-profile option. 

Low-profile systems tend to have smaller diameter pipes and run at a higher temperature. This means that the floor will heat up and cool down far more quickly than conventional underfloor heating.

Where underfloor heating is added to an existing radiator system then a different control system will be needed. Luckily, wireless thermostats (some of which can be controlled with a phone app) make installation far easier.

(MORE: How to Retrofit Underfloor Heating)

Is Underfloor Heating Expensive to Install?

Underfloor heating costs from around £20/m2 to £40/m2 installed. These figures will vary depending on the size of the property, the amount of heating the building needs and whether it is a new build, renovation or conversion.

Can Underfloor Heating Replace Radiators?

Potentially yes, but this will be dictated property by property, room by room, depending on heat loss and whether the output from an underfloor heating system is larger than this loss figure. 

Radiators are cheaper to buy, they are well understood and there is a huge choice when it comes to size, style and installers, but they are less efficient and take up floor space. Perhaps the biggest problem is that in larger rooms they can produce a temperature difference of up to 4°C across the room.

An underfloor heating system also offer a 15% reduction in energy demand compared to a radiator system, which is hard to ignore. 

What are Cheaper: Radiators or Underfloor Heating?

While underfloor heating has a higher initial expenditure than radiators, don't let this put you off. The running costs are generally far lower for UFH than radiators. It's worth noting too that underfloor heating systems have a lifespan of 50 years plus, while the average radiator will only last between 8-12 years before becoming inefficient. 

How Thick a Screed Do I Need with an Underfloor Heating System?

The thickness of the floor screed during your installation process will make all the difference. The screed thickness in which the warm wet pipes sit will have a dramatic impact on how the system is used.

A thick screed will give a longer reaction time (the time taken to warm up and cool down), while a thin screed will have a quicker reaction time.

Creative Commons Attribution-NoDerivatives 4.0 International Public License

The thickness of a screed laid over an underfloor heating system, like this one from Continal, will affect how it operates. (Image credit: Continal: Creative Commons Attribution-NoDerivatives 4.0 International Public License)
  • If the pipes are housed in the concrete floor slab (sometimes the case for new homes), this should be 150mm thick and give a reaction time of over four hours. In this situation, it is best to run the system all day, at a lower room temperature — say 15°C or 16°C — to provide background heating to the whole house. Highlight heating, such as a log burning stove, is a good idea in the rooms that are occupied
  • A standard sand and cement screed would typically be 65mm to 75mm thick and the underfloor heating could take upwards of two hours to heat the room or cool down. This situation may be well-suited to rooms where we spend a lot of time, such as lounge or kitchen, but might be less acceptable in a guest bedroom
  • With thinner flow screeds, we might expect a thickness of 35mm to 40mm and a reaction time of around 30 to 40 minutes — the system can be run in a similar way to a radiator system. Flow screeds offer better thermal conductivity than sand and cement, and being thinner and lighter means that they can be suitable for both renovations and new builds

Which is right and best will depend on the construction of the house, your occupation habits and how the underfloor heating system is to be used.

(MORE: Underfloor Heating Installation)

Will Underfloor Heating Raise my Existing Floor Profile? 

Underfloor heating will usually raise the profile of the floor. The amount it is raised by will depend on a number of factors such as how much insulation you need to add, pipe size, and whether you need a screed and floor finish. 

There are however some products that get ‘carved’ into an existing screed, in which case there would be no additional build up other than the final floor finish.

Which Types of Flooring are Compatible With Underfloor Heating? 

Speak to Your UFH Designer

It's a good idea to tell the underfloor heating system designer the type of flooring you're using so that the pipe layout can be properly specified.

There is a belief that underfloor heating can only be used with tile or stone flooring, and while it is true that it does work well with hard floors, it does not follow that other floor coverings are precluded. 

Wood, for example, is fine so long as it is thin profile (12mm or 15mm) engineered timber. Engineered timber will deal with the temperature changes and has little noticeable impact on heat output. Never use solid wood flooring with underfloor heating, as it cannot cope with the temperature changes and may warp and become severely damaged. 

Carpet has generally been considered a no-no in the past, but the Carpet Foundation carried out some research with the Underfloor Heating Manufacturers Association showing that a carpet and underlay with a thermal resistance of less than 2.5 tog does not have a significant impact on efficiency. According to the Carpet Foundation, a typical 80% wool to 20% nylon carpet with a standard underlay will have a tog value between 1.0 and 2.2. 

(MORE: Types of Flooring

You can place a rug on underfloor heating, but it will affect the heat output. If you plan to put a rug, or furniture for that matter, in a room then it is best to design the pipes to be a lot closer together, around 100mm, so that there is enough length exposed to a free surface

Controlling an Underfloor Heating System 

underfloor heating controls being installed

It's easy to control your underfloor heating and zone off certain areas as seen being installed by JK Heating. (Image credit: JK Heating)

Underfloor heating system controls feature two main parts:

  • A digital zone control that will be used to determine the temperature of each room/area
  • The manifolds and valves that the zone control operates

The zone control will be placed somewhere where the homeowner can make adjustments, while the underfloor heating manifolds will be placed out of the way – under the stairs or in a cupboard – so as to be unobtrusive.

There is no regular maintenance regime associated with underfloor heating, but if things do go wrong, it will typically be with the heating control systems rather than the system itself.

(MORE: Underfloor Heating Manifolds)

Choosing the Right Underfloor Heating Supplier 

Ultimately, the efficiency and success of an underfloor heating system will depend on the quality and design. Choosing a supplier who offers a good design service and aftercare is important. A specialist underfloor heating company is often best placed to achieve this.

If the design is wrong it is unlikely that the homeowner will know until they have lived in the house for a whole heating season — by which time it might be too late.

Finally, if you are choosing to pair underfloor heating with an air source heat pump or ground source heat pump, it is a good idea to choose one supply and install company. Both are complex systems and getting the whole heating system to work in perfect harmony can be tricky.

Tim Pullen

Tim is an expert in sustainable building methods and energy efficiency in residential homes.