Just about to re-fit my bathroom and as it's on the ground floor and the floor is tiles on concrete i will be fitting an electric underfloor mat heating system. The room is small, 6 sm m and the mat will only need to cover a 2 sq m area where foot fall is.

However I have seen differing opinions as to whether it is worth laying insulation boards under the heating mat. I would like to get away without adding insulation as it will hadd cost, floor height and hassle. Some estimates on payback form the insulation (which would be 10mm max) is 30-40 years. The under floor heating will not be the primary heat source either, will just be on for 30 mins morning and eveing to take the chill of the floor.

There is an interesting thread on piston heads
http://www.pistonheads.com/gassing/topic...floor&mid=0
But I cannot decide who is right and my A level physics has long since been forgotten.

Help and advice please.

just in the process of fitting underfloor heating on concrete. Insulation boards apparently decrease the warm up time by quite a big margin. if you look on warmup website (if you do check out their new thermostats, look great) they have a comparison. From memory reduces times from 2.5 hours to reach a certain temp down to under 30mins.

With the floors fitted in the past we only use it to take the chill off like you suggested, so maybe less time difference. i can't recommend fitting underfloor heating enough when laying tiles, makes such a difference.

You must fit insulation boards, why pay to heat up the concrete? it'll takes ages to warm up without them. Warm up is the one we use at work.

Well that is one argument, another is that the heatsink effect keeps the tiles warmer for longer

Looked at the warm up stuff, looks good but crazy expensive compared to other similar systems.