Underfloor heating (UFH) offers a promised 10-45% saving of the energy costs (carbon emissions and fuel costs) associated with heating a home. Underfloor heating has the advantage that you regain the room and wall space used by radiators, but it takes slightly longer to heat the room from a cold start than it does with radiator-based central heating.
How does it work? The basic principle is that heat slowly radiates from the ground upwards. It is a much more efficient way of creating comfortable room temperatures as it fits with the natural requirements of our bodies. This is because human beings tend to emit a higher proportion of heat through our head than our feet so we feel the cold first through our feet and legs and then though our arms and torso. This means that underfloor heating produces the ideal heating environment - one where the temperature reduces on a gradient from floor to ceiling. By contrast, conventional radiator heating works in the opposite way. First the air next to the air next to the radiator which than naturally rises up the walls and spreads out across the ceiling until it reaches the centre, where it cools slightly and then descends. This creates the reverse, in other words a heat gradient that reduces from ceiling to floor so the net effect is that to obtain comfortable levels of warmth in our feet we need to over heat our head and torso therefore using much more energy than is really required.
In addition because underfloor heating spreads heat over the entire floor area rather than being concentrated in 1 or 2 square metres of radiator panel as a proportion it generates much more radiant heat (approx 50%) than conventional radiator systems. Radiant heat is considered to be the most comfortable form of heat, gently warming our bodies in the same way that the sun does on a summer's day.
There are two basic technologies; electric underfloor heating and 'wet' or water based underfloor heating and whilst it is more costly and complex to install the water-based systems are generally recognised as the more energy efficient.
Electric UFH: These systems comprise of electric cables or foil and have the advantage over wet systems of being thinner - typically only 10-15mm of floor height including the new floor covering. Most importantly cable and foil systems are much easier to fit and can be easily retro-fitted with existing floor structures, so are much better suited to renovation and upgrade . Cable systems are usually laid directly into concrete floors for new builds, or in the case of retro fit can be laid on the existing sub-floors in cable mats, which can be cut and bent to shape. Foil is the thinner electric offering, but is less flexible as the sheet are in square or rectangular format and cannot be cut to suit awkward room shapes and sizes.
Electric UFH works on the same principle as storage heaters and where for example in new builds the cable is laid into the concrete floor , the floor acts as the thermal mass to slowly release the heat in the same way that thermal brick act in storage heaters. Where the cable is retro-fitted on top of existing sub-floor structures, the cable is laid into a thin layer (approx 15mm) of specialised thermal screeding. In the case of foil or mat which is laid on existing sub floors heat spreading tiles are used to cover the elements. Carpets and Underlays need to be replaced with Hessian backed carpet with a low Tog value (< 2.0) and low Tog value underlay (<0.8 - 1). Underfloor heating can be used with most types of floor covering but we strongly recommended you check with the manufacturer to ensure your choice is suitable for use with underfloor heating systems.
In both cases, if your house was built before about 1980 you are likely to need add insulation on top of the existing sub-floor construction otherwise any efficiency gain will be lost by heat dissipation through the sub-floor.
Wet or water based systems consist of loops of plastic or plastic-coated metal pipes laid within the sub-floor structure (screed) usually at a depth of between 60- 85mm. For this reason 'wet' or water-based systems are most suitable for new builds, as in the case of retro-fits the entire sub-floor structure will need to be dug out or the floor height raised by about 10cm. Heated water is taken directly from your hot water system, which can be a condensing boiler, solar panels or most efficiently from a Ground Source Heat Pump (see our info page on GSHP's). The water is then regulated to a temperature of between 45 - 65 degrees Celsius and circulated through the piping. Once again if carpets are required, they should be low tog and used with a log tog underlay and any intended covering should be checked with the manufacturer to ensure its is suitable for use with underfloor heating systems. Timber coverings must for example have moisture content of below 10% or they are liable to warp.
Other potential benefits of underfloor heating include:
- Underfloor heating producers a lower room moisture content than radiator
heating and so discourages dust mites.
- Under floor heating ais silent and does not suffer from the gurgling and
knocking of radiators.
- Cleaning of floors is easier and washed floor surfaces will dry faster.
- No peeling of wall papers or cracking or discolouration of paint finishes
behind radiators.
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