In this post we speak to Martyn Neil, Wavin Business Development Manager for Indoor Climate Solutions about the use of carpets and underlay floor finishes with underfloor heating.
One question I am regularly asked is whether underfloor heating works with all types of flooring. Due to the popularity of carpet in the UK, developers, designers, installers, and homeowners often ask about the use of hydronic underfloor heating systems with carpet and underlay floor finishes.
Perceptions of Underfloor Heating, Carpet and Underlay
• A research survey of housebuilders, installers, and homeowners into the use of underfloor heating with carpet and underlay found:76% of housebuilders reported an increase in demand for underfloor heating, mainly in higher end properties
• Housebuilders who responded rated themselves as having a low knowledge of underfloor heating, underlay, and TOG ratings
• 54% of installers reported an increase in demand for underfloor heating on projects in the past 12-18 months
• Only 20% of installers said they were fully aware of TOG ratings and what they should be for installations with underfloor heating
• 21% of installers reported being asked to install underfloor heating with carpet in the past 12-18 months
Advantages of Underfloor Heating
Underfloor heating involves the installation of pipes underneath the floor covering, either in screed (new build) or on a plate/low build board (retrofit). Underfloor heating provides radiated heat rather than convected heat which radiator systems provide.
Radiated heat via underfloor heating has the following advantages:
• Surveys show homeowners prefer underfloor heating as it provides more useable living space with no radiators on show which helps gives rooms a cosy feel
• Room layouts have complete flexibility with no radiators on the walls to be accommodated - providing an even distribution of heat, spaces can be zoned to suit individual or specific lifestyle needs
• Heating can be controlled by smart technology from inside and outside the home, and is more sustainable than traditional heating systems
• The indoor climate is healthier as less dust is circulated in the air when using an underfloor heating system, which is better for allergy sufferers
• Underfloor heating is a safer system as the risk of scalding is minimized
• Underfloor heating is low maintenance with no damaged radiators and less bleeding of air from the heating system
• The flow temperature required from the heat source can be reduced, making it a more efficient system, and suitable for heat pumps
Advantages of using underlay with Carpet
Carpets are the leading floor covering for the average British home, with a market size of over £1.7bn per annum. Underlay is part of providing the key advantages of carpet systems, which add:
• Additional comfort- provides a dense layer of additional cushioning underfoot
• Sound insulation- reduces the noise within a room by up to 30%, with the benefit of reducing transfer to other rooms
• Extended lifespan of floor- can provide extra protection in high footfall areas, by acting as a shock absorber retaining the spring of the carpet
• Improved appearance- Underlay will help to preserve the appearance of the carpet
Homeowners can find solid floor systems noisy without the sound insulation of a carpet/underlay system.
Using Carpet with Underfloor Heating
The key challenge to overcome when combining carpet and underlay with an underfloor heating system, is that the insulating benefits that come with carpet, is to the detriment of heat transfer. We are heating the air using warm pipes under the floor covering, the higher the resistivity of the floor covering the less heat transfer from the underfloor pipes to the air. However, this challenge can be overcome to enable the carpet & underfloor heating combination to work collaboratively by making sure the correct TOG rating is used on the carpet.
The UK Government as part of the Future Homes Standards consultation documents, have published a draft Approved Document Part L, which covers the ‘Conservation of Fuel and Power ,and Minimisation of Greenhouse Gas Emission’s. This may not be the final Future Homes Part L document, as its under-consultation, but it gives a strong indication of Future Homes Standards for England from 2025 onwards.
In Future Homes Part L section 6.38 it states:
In new dwellings, the total thermal resistance of all floor coverings used above underfloor heating systems should be 0.15 (m².K)/W or less. This means that some types of carpet floor coverings may be unsuitable for use with underfloor heating systems.
Resistance of 0.15 m².K/W is equal to 1.5 TOG and this means it is likely that this will be the maximum resistivity in new build homes.
To calculate how this impacts the performance of the underfloor heating system, the following elements need to be considered.
Required Heat Output
The heat output required is the amount of space heating load needed for a zone or building. Part L indicates the methodology used in BS EN 12831-1 and a methodology that considers the properties of the dwelling, should be used to calculate the required heat load.
Heat Output Provided by the Underfloor Heating with Selected Floor Covering
Once the amount of heat required in the zone is established, a calculation can be done to determine the specification of the underfloor heating system required to achieve that load.
Underfloor heating outputs are determined by the following factors:
• Flow temperature of the heating system-Part L 2025 determines this can be up to 55ºC
• The amount of pipe in the room-Typically 150mm pipe centres are used in new build dwellings with low temperatures. This can be reduced to around 100mm, depending on pipe size and type, to provide more heat where required
• Flooring system used-Underfloor heating can be installed in screed or using low build boards installed on an existing floor. The floor system used, and its thickness will vary the heat output
• Thickness of the floor finish-The thickness of the carpet, wooden floor, or tiles will have an impact on the heat output
• Resistivity of the Floor Finish-As described, the maximum tog rating for new build is likely to be 1.5 TOG (0.15 resistivity) from 2025 onwards
Given this information Wavin can design an underfloor heating system that will ensure the systems heat output is greater than the required heat load. Engineered solution can be found to improve performance where required, such as suggestions on the optimal flow temperature, pipe spacing, and flooring systems to ensure homeowners receive a comfortable amount of heat, with any floor finish.
What Heat Outputs Can Underfloor Heating with Carpets Provide
Heat outputs from underfloor heating are commonly expressed in W/m² (Watts per metre squared). To calculate the heat output from the underfloor heating system, multiply the heat output by the size of the heat area in the room. Typically this is the entire floor area of the room, minus any fixed cupboards or islands.
Retrofitting Underfloor Heating
Guidance on new build and deep renovation is clearly defined in building regulations, but in some cases homeowners with an existing floor finish may wish to install underfloor heating in an existing dwelling. Here the methodology to calculate heat load requirements and outputs are similar to new build.
A survey is required, using a thermal model, to determine the required heat load for the zone and building. This will determine the heat load based upon factors such as the buildings construction and heat source, to give an accurate representation of requirements. Then Wavin can support the selection and specification of a suitable underfloor heating system to deliver the heat load, considering the floor finish used. Putting Carpet on an
Existing Underfloor Heating System
Where a zone or building has an existing underfloor heating system, and the floor finish is planned to be changed, then a new calculation of the heat output versus heat load requirement should be made. The simplest approach may be to find the documentation provided with the underfloor heating system, and request the supplier provides a re-calculation of the system with the new floor finish.
Can underfloor heating be used with Carpet and Underlay Floor Finishes
In a home built to current regulations, the efficient fabric of the building results in lower heat losses than UK houses had in the past. Efficient building design makes heat load demands lower, and the required output from the underfloor heating system is reduced.
Carpet is an extremely popular floor finish in new builds, especially in first floors and above, which benefit from rising heat from the ground floor.
These factors means that a well-designed underfloor heating system and low TOG carpet/underlay combination can be used to provide the benefits homeowners enjoy.
In retrofit and renovation projects, where underfloor heating is being installed in an existing home, or where carpet is being installed on an existing underfloor heating system, care must be taken to ensure the heat output of the heating system exceeds the heat load requirements. Here a survey is required to make the calculation on how much heat is required versus the heat output of the existing system.
It is important to seek advice from specialists in carpet, underlay, and underfloor heating.
Wavin’s Indoor Climate Solutions team are leaders in providing underfloor heating solutions to the UK market. As a UK manufacturer, Wavin provide specialist underfloor heating pipe, manifolds, and controls, with flooring systems to wholesalers, installers, and developers, along with a broad range of hot and cold pipe solutions, drainage, and rainwater solutions.
For further information or specific system guidance, please get in touch below
