I have fitted UFH (Eco-Hometec) to our new kitchen/utility room and I'm gradually ramping up the temperature now (so as not to damage the screed). The (very poor) instructions from Eco-Hometec suggest the water inlet tempertaure should be set to 55degC. Currently I'm at just over 40degC and the room is warming up nicely. I should say the floor is ~25degC with my calibrated palm.
Is there an accepted temperature these systems should be run at? Presumably there becomes a point at which the screed can be damaged through thermal expansion and contraction.
Is there an accepted limit on floor temperature? Obviously you don't want people hurting their feet first thing in the morning.
Finally, does anyone have any experience using Karndean vinyl flooring with UFH? http://www.karndean.com/home.asp Karndean say it's OK up to a floor temperature of 29degC, but won't say what happens above this. Also they have no U-value data they are willing to share which concerns me. The benefit is the slightly more forgiving surface (compared to porcelain tile) and the variety of finishes. Also although it's ~£50 p/m, probably cheaper than floor tiles once fitted. (I'll get someone in to do the floor - newborn + 2 toddlers has severely limited my DIY time! I did install the UFH though, so I don't feel /too/ guilty!)