Wood floor thickness and heat resistance over UFH

The maximum resistance floor covering with a boiler feed system is 2.5 tog – 0.25 W/m2k. The lower resistance the better the performance and energy efficiency of the heating system. At this higher limit the operating temperature of the floor needs to be as high as 55ºc.

With ground source or air to water heat exchangers the highest operating temperatures achievable are 41ºc at a push. This means that the resistance of the floor covering needs to be kept to a minimum. Fermacell (Gypsum fibre board) is the desired substrate to be used in this situation due to its low resistance.
(There are on site difficulties with the use of `Fermacell due to the fact that it can not be walked on unless fully supported, so over joist etc crawl boards will be required).

In the event that CF needs to be raised above a screed to obtain corrected levels Fermacell may be the only product suitable to built up in layers, as a substrate to minimise the resistance calculations.
Fermacell has an advantage of being laid at a thickness of 205.5% more than wood. The resistance of 20 mm of wood is equivalent to 41.1 mm of Fermacell.