Hi,
I am starting to look into floor screeds. I see that the liquid floor screed claims the usual " UP TO 30% MORE EFFICIENCY" with UFH than normal concrete floor screed. I know concrete is very bad but is the liquid screed more thermally efficient or is it just the sales pitch and maybe it is 1% more efficient? I would just like to know if the efficiency figures carry any weight? Does anyone have any information on the liquid screed systems? Thanks,
Gusty.

It's not an easy question. If you put a carpet over your UFH the heat output into the room is reduced but you can correct that by increasing the flow temperature within reason. Any loss of efficiency really depends on what impact increasing the flow temperature has on your heating system as a whole. It may have a only modest effect on a gas boiler but a much greater effect on an ASHP (because the COP of ASHP is more critically dependant on flow temperature). However in many systems the boiler is producing water thats too hot for UFH anyway and a mixer has to be used to drop the flow temperature for the UFH.

You do need to be careful because some screed companies put materials (eg Vermicite) in the screed to make it a more efficient INSULATOR. I once read a post from someone who had accidentally used aerated screed over their UFH. No matter what flow temperature they used they couldn't get enough heat out of the floor to heat the house and the return temperature was practically the same as the flow temperature. The boiler was cycling like crazy as the boiler flow temperature kept maxing out.

Some example figures:
Flo-Screed say their liquid screed has "Excellent thermal conductivity (2.2W/Mk)"
I think ordinary screed around 1.4-1.7 W/MK ?

I'll let someone else work out how much they could increase the TOG value of their carpet if they used liquid screed rather than ordinary screed

Gusty
Let us all know what they say please. All information is useful.