Underfloor heating is an increasingly popular option, but there’s a lot to consider before installing it in your home. This guide explains everything you need to know .
Underfloor heating is a system that effectively turns your floor into your radiator. Underfloor heating works really well with renewable technology like heat pumps, and can help to prevent cold spots and draughts in your home.
It also works at a lower temperature (40°C) than a standard radiator system (65°C), which means less demand on your boiler for the same, if not improved, level of comfort.
The installation of underfloor heating also means that walls are left unobstructed which is great for those looking to keep clean lines as part of their interior design aesthetic. Without the need for radiators, homeowners can find themselves with more flexibility when it comes to furniture layout.
While best installed as part of a new build house or extension, it is possible to retrofit underfloor heating into an existing home by choosing a low profile option.
What is Underfloor Heating ?
Underfloor heating involves the installation of pipework in the floor, so that the whole floor acts like a radiator, warming the room from the ground up.
There are two main types:
(which we will focus on in this article)
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 screed.
Underfloor heating is more expensive to install than a comparable radiator system — it typically costs 60% to 90% more.
Is It Worth It?
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.
People want more energy-efficient houses and a system that gives a 15% reduction in energy demand (compared to a radiator system) cannot be ignored .And that is to say nothing of the greater comfort and the increased floor space that it brings.
What Thickness of Screed Do I Need to Use with Underfloor Heating?
The thickness of the screed 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.
Here, screed is being laid over warm water underfloor heating pipes to the correct depth.
If the pipes are housed in the concrete floor slab (sometimes the case for new homes), this is could 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 woodburning 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 UFH 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 UFH system is to be used.
Which Floor Coverings Work Well with Underfloor Heating?
Tiles, stone or similar are generally accepted as the optimum covering. They absorb heat rather than insulate and allow that heat to radiate into the room
Timber flooring will tend to insulate and reduce efficiency, but thinner profile engineered timber has little noticeable impact on heat output. Solid timber is notoriously tricky with underfloor heating — it needs to be acclimatised for around a month
The Carpet Foundation carried out research in conjunction with the Underfloor Heating Manufacturers Association which shows that some carpets can be used with UFH. The research showed that a carpet and underlay with a thermal resistance of less than 2.5 togs does not have a significant impact on efficiency
Whatever floor covering is to be used, it is a good idea to tell the underfloor heating designer so that the pipe layout can be properly specified.
Underfloor heating pipes are laid in different zones/rooms/areas, allowing the homeowner to control the temperature in each separate zone.
Underfloor heating system controls feature two main parts:
The zone control will be placed somewhere where the home owner can make adjustments, while the 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 control systems rather than the system itself.
How to Install Underfloor Heating ?
The first step is to connect the floor heating pipe to the manifold.
After laying your insulation layer, you will need to begin to lay the pipe.
Secure the pipe to the insulation as you go using pipe staples.
Ensure you fix the pipe with the correct spacing to ensure optimal heat distribution.
Loop the pipe across the whole floor area. Use multiple loops for large spaces.
Prepare the screed (or opt for a ready-mixed version).
Carefully pour the self-levelling screed over secured pipework.
Stabilise the screed with a chemical spray.
Finally tamp the screed for a smooth finish.
This diagram shows a typical build up on a concrete subfloor
If you are opting for a whole-house underfloor heating system, there will be separate pipe runs 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.