Underfloor Heating

Continuing his guide through the world of renewable energy, Richard Williams looks at the case for installing underfloor heating...

Last month I looked at the case for air source heat pumps (pompe � chaleur), specifically at their advantages over ground source heat pumps. Of course, having captured this heat in a highly efficient way, we need to find a way to distribute it around the house.There are a number of options open to me and, like many, I’m constrained by budget, while at the same time trying to get the best possible performance. At the end of the day, I’m living in a small two-bed farm cottage. While I am keen that my renovations are as eco’ as possible, there is going to be a limit as to the return I’ll get on my investment.The most flexible ASHPs transfer the heat from (outside) air to water; this means we can then seamlessly integrate the system into an existing space heating system, via radiators, and hot water heating system, through the hot water tank. I don’t yet have a radiator system installed and, in the heat of July, the cold winters of Burgundy seem a long way off, although I know that the planning of this is something that I really do need to turn my attention to.With a relatively small house, I’m confident that I can install the radiator system for well under €1,000 by doing the job myself. That said, we have many heating engineers in the vicinity (they all seem to advertise fairly widely), a sensible option for the DIY-averse.It is true that the temperature of the radiators will be nearer 55oC, rather than the 60-70o C that we are used to, but this is a small price to pay when the greater efficiency of the system is taken into account.From the air to the floor to the airWhere the ASHP really comes into its own is when underfloor heating comes into the equation. Underfloor heating may be run as low as 30oC, which by asking the ASHP to provide less energy than needed for a higher temperature, gives much greater efficiencies, up to a CoP (coefficient of performance) of 4.My challenge is that the floor I’ve identified for underfloor heating is in a barn that I’m converting, and is suspended wood. There’s a garage underneath so I need to be sure that the joists will be strong enough to do the job. The usual approach for underfloor heating is to lay insulation followed by the heating circuit and then a depth of screed to act as a slow release energy store.The weight of this conventional approach will be unacceptable as I am reluctant to go down the route of replacing the joists with steel beams; cost is always in the background! I could remove the floorboards and run the insulation and pipework between the joists, with a thinner coat on top. I’ll let you know how this develops.My neighbours have installed an electric system with a very low-weight concrete mousse as the storage medium. They are pleased with it, but due to its high volume, this isn’t really something I could consider; doorways would become even lower and I’m a tall chap!The final floor surface will probably be tiled. I say probably because the ultimate look of the room is still a long way off! Tiles work well with such systems, but wooden floors need to be approached with caution as they may warp with the heat. Thick carpets and insulated cork should really be avoided as their thermal properties can reduce the efficiencies and reduce or even outweigh any benefits.Efficiency is not the only reason for wanting underfloor heating; I’ve great plans for this room and the aesthetics will be important to me, so the lack of intrusive radiators is a real plus. Traditionalists, fear not, I’m still looking to keep the traditional feel in the main part of the house. That said, at the moment I have no radiators in the house, as that was how it was built. How much more traditional can I get?Underfloor heating is not cheap. Around €50-80 per square metre is not unusual, with lower profile floors commanding higher prices. The DIY approach is an option, but I’d only recommend that if you are a very proficient plumber, because once the floor is down, you really don’t want any leaks. So the story with underfloor heating is one of balancing comfort with cost. Next month, I’ll take a look at a less expensive option I’m considering at the other end of the spectrum.Story by,Richard Williams runs Burgundy Energy, an independent energy consultancy that provides advice and project management