Question from Paul Jansen, via e-mail:
I’m considering underfloor heating (UFH) underneath a wooden floor in the living room of my Victorian house. The ceiling is three metres high. My questions are:
– Do I need to keep the UFH on all the time?
– I hear the temperature can only be adjusted by 1ºC per day. How does the system cope with temperature fluctuations not uncommon in England?
– Is it expensive to run, especially if it needs to be kept on all the time?
– Should I consider radiators in addition to the UFH?
– How much would the installation costs differ between an UFH installation and installation of radiators? The room is approx 30 square metres.
Answer from Martyn Bridges, director of marketing and technical support at Worcester, Bosch Group:
Underfloor heating is a particularly beneficial method of heating a house, providing numerous features over the more traditional radiator system. In the early days it was only suitable for new build properties with solid floors. However, new developments and enhancements have made it suitable for both existing and new properties with products for both solid and suspended or wooden floors.
From your description you suggest that the room is quite large and tall and it may be therefore necessary to keep the UFH running for 24 hours, or longer than perhaps traditional radiators would need to be on.
An accurate heat loss calculation of the room needs to be undertaken, this would then enable the amount of underfloor pipework and the duration of running times etc. to be ascertained.
It would be unusual to require an UFH system to run for 24 hours, however, it is not unusual for the system to be ‘available’ for 24 hours and using a programmable room thermostat differing room temperatures for different times of the day can be programmed.
I agree that because of the thermal mass of a solid floor, it can take some hours to affect the air temperature of a room. With your situation of a wooden or suspended floor, this isn’t the same, so yes it is a longer time than radiators, yet nowhere near as long as solid floor.
UFH is normally quite economic to run as the flow temperature is quite low, so if run from a condensing boiler then the boiler would condense more and if from a renewable technology, such as a heat pump, then the coefficient of performance is high. I am not aware of any laboratory comparisons between UFH and radiators, however, it is normally accepted that a minimum 5% improvement over radiators is achieved.
My suggested way forward would be to get your installer to engage an UFH company to undertake a heat loss calculation and then size the amount of underfloor pipework and operating conditions etc. Most UFH manufacturers will do this, some of them will do this free of charge.