Underfloor heating is more effective if the insulation under the floor and at the floor edges is to a high standard. This is because well insulated rooms prevent heat being lost into the walls and ground.
There are two main floor construction options available when considering an underfloor heating system. In this section, information on both is available along with the advantages and disadvantages of each option.
Solid Floor Construction
The most effective and economical method of installing underfloor heating is within a concrete screed or slab, as the heat output is higher than with any other floor type. Concrete absorbs heat – much like the way in which a stone fireplace works – this allows the heat that’s been stored within the concrete to be dispersed evenly.
Fixing the pipe to the insulation on a screed or solid floor also offers a variety of options:
Rail Fixing – This system is low cost and easy to install. A plastic pipe clip rail can be used with any type of insulation and allows for variable pipe spacing. This system is used in conjunction with staple fixing, explanation below.
Staple Fixing – This is the preferred method by professional installers as it’s a faster installation process. It also allows for infinitely variable pipe spacing to give the correct heat output for any area. Staple fixings work with most types of floor insulation, including Polystyrene EPS 100, Polyfoam and Polyurethane and usually combines with the rail fixing system, as described above.
Pipe on Mesh – This method is the cheapest of UFH methods, this is because most buildings will already have a structural slab in place. The method requires a steel wire mesh to be laid over an insulation layer, special insulation is not required though. It also allows for variable pipe spacing. However, there are drawbacks with this system: laying mesh and fixing pipe to mesh is more difficult than other systems and wire mesh is often an unnecessary adage in screed floors. This system also needs to be pressure tested before the screed is laid and the pressure must be maintained during the screed being poured.
Suspended Floor Construction
Underfloor heating traditionally relies on the thermal mass of a concrete floor or screed for heat. As the heat that is stored with the concrete disperses, it is evenly distributed into the room. However, it is possible to achieve this effect on a suspended floor by means of laying the pipes in a dry screed (pug/biscuit mix), or with aluminium diffusion plates between timber joists. The flooring would then be laid over this.
Compact Flooring System
This low-profile method allows underfloor heating to be installed in spaces where typical UFH systems would require costly excavation or where the floor would need to be raised too high for the profile of the room. Overlay can be applied to all build types and floor coverings and the panel is made up of a fibrous material.
This system provides ideal response times and a solid heat output compared with more traditional built-in UFH systems. It’s an ideal method, which avoids the sometimes expensive and messy work involved in other UFH systems. It can be applied to traditional heating systems and low temperature renewable systems.
UFH systems can be fitted using a number of methods, including:
Pipe In Plate
In a timber suspended floor, insulation should be fitted below the metal diffuser plates eliminating any air gaps and ensuring that the heat is transferred up through the floor. The pipe is fitted into preformed grooves within the plates, which in turn, transfer heat evenly through the floor.
Pex AluPex multi-layer pipe should be used in conjunction with the plated system due to its reduced coefficient of expansion. This results in less movement within the plate during warm up and cooling, giving less chance of expansion and contraction noises.
Advantages of the Pipe In Plate system
- The plate has a lower thermal mass than a pug system, this speeds up response time and makes controlling the system easier.
- This system benefits from a quicker installation time than other methods and requires less material or labour by the builder. There’s also no additional costs and no drying time is required.
Pipe In Pug
In timber suspended and batten floor construction, the pipe is laid and stapled onto an insulation layer, onto a plywood base, between joists or battens and covered with a dry sand and cement mix. Rails can be used to fix pipes between joists and battens. Variable pipe spacing can be achieved with this type of construction, as well as good heat outputs.
However, consideration should be given to the additional weight in suspended floors, a typical 35mm pug mix will add around 35kg/m2 of dead load. Please take this into consideration before laying an underfloor heating system.
Advantages of a Pipe In Pug system
- Utilises the thermal mass of the screed.
- Can give a higher heat output.
- Quick drying time.
- Cheaper for the underfloor heating materials.
Screed is usually a layer of cementitious material, which is usually applied over the water pipes and insulation in UFH systems. It creates a smooth and level surface for the UFH system to operate efficiently in. The screed mix must be able to withstand temperature changes without cracking, so it’s an important element to consider early on in the design phase of any UFH system.
There are different types of screed, including:
- Sand & Cement
- Sand and cement enhanced screeds
- Anhydrite (Calcium Sulphite) screeds
- Liquid Cementitious Screeds
Advantages of Screed
- Large thermal mass – as the UFH pipe is encased within screed, this acts as a large radiator that will hold heat for a long time.
- Lower water temperatures – most UFH systems encased in screed will operate at a lower water temperature making the overall system more efficient.
- Variable pipe centres – the UFH pipe can be installed easily at various centres to achieve different heat outputs in different areas.
- Higher heat output – warm water UFH within a screed will achieve the highest output (up to 120W/m2).
- Cost effective – as most buildings require floor insulation to meet building regulations and screed is included within the floor build-up. A screeded system can be the most cost effective UFH system.