Darren Trivett of Ridgespear Group offers insights into why developments in underfloor heating make it a practical option, and gives some installation tips
The commonest forms of underfloor heating (UFH) involve circulating water through a high-performance plastic pipe, set within the structure of the floor. This water can be heated efficiently by a conventional gas or oil boiler or by solar thermal panels, or it can be heated (or cooled) very efficiently using a heat pump.
If you circulate cold water through an underfloor heating system during the summer, you can create a comfort-cooling system. A heat pump can use electricity three to four times more efficiently than electric underfloor heating, and electric underfloor heating can never provide cooling.
UFH has become the preferred form of heating throughout the residential sector – from top-end through self-build to local authority and housing associations. It is also now commonly specified for schools and medical facilities, for offices, factories, boats and even zoos.
There are three ways in which heat can be transferred into a room – conduction, convection and radiation. UFH mostly uses radiation which is the most natural and comfortable form of heating (think of sunbathing) – we like radiant energy. UFH is safe because there are no hot surfaces, it is unobtrusive, more hygienic and more energy-efficient.
Radiators, by comparison, mostly use convection to heat a room. They heat the air, which becomes buoyant. This rises to the ceiling and travels across the ceiling to the far side of the room. As it cools, the heated air drops and returns across the floor to the radiators to be reheated. This convection cycle, as we call it, inevitably puts the hottest air in the room at ceiling level and the floor is always the coldest part of the room. With UFH, the temperature in the room is very even and the floor is the warmest part.
With UFH, the floor surface is made about as warm as the palm of your hand (25 – 27°C). The right form of UFH can achieve this surface temperature using water which is much cooler than even over-sized radiators require. If your heating system can be effective while using cooler water, then not only is this more energy-efficient but it also opens up the prospect of being able to obtain this lower temperature water from renewable energy sources. UFH has the potential to wean buildings off their dependency on continued availability/affordability of fossil fuels.
Most UFH suppliers ought to be able to supply an effective form of UFH when it is set within a screeded or concrete floor. It is just a case of installing the correct amount of plastic heating pipe over the top of the insulation before the screed or concrete is laid, and then making sure the screed/concrete fully wraps around the pipe. If you pin the pipe directly to the top of the insulation, it can be damaged when the screed is moved across the top in barrows and the pipe can often be kicked loose when liquid screeds are laid over the top.
Fixing clip-plates across the top of the insulation and then plugging the pipe into these protects the pipe and holds it securely in place while the screed or concrete is laid.
Many buildings in this country are now constructed with timber floors. There are some flooring companies and even some underfloor heating suppliers who say that underfloor heating should not be used in a timber floor because timber is a poor thermal conductor.
This is because they have either not used the correct form of underfloor heating in the past or simply because they don’t have it in their product portfolio. The truth is that the correct form of underfloor heating can be very effective and the best way of looking after a timber floor throughout its lifetime, if you do it right.
Recent changes to SAP have had the effect of giving a building a better energy rating if it has UFH in a timber floor than if it has UFH in screed/concrete. The improvement in SAP is sufficient that, if a house has timber UFH which is powered using a ground-source heat pump, a house which would otherwise be rated Level C could instead have the potential to be rated Level B. The most important reason for this is because timber floor constructions have lower thermal mass than screed/concrete and this enables timber UFH to change heating power output more quickly and with a smaller injection of thermal energy.
However it is important to make sure you choose the right underfloor heating system for timber floors. Not all systems work in the same way some require very high water temperatures to be effective. So it is important to ask the supplier for independent heat output test data to make sure it will provide enough heat, especially when using a heat pump.
Darren Trivett is CEO of Ridgespear Group