Underfloor Heating - Tiling over tiles

[North Longford]

If there are any underfloor heating gurus out there help would be greatly appreciated.
Have underfloor heating in the house some of which is tiled over.Now there are suggestions that the tiles are no longer that nice!!!! The choices are lifting and and re-tiling....quite arduous or just tiling over the existing tiles. Question is would this have much of an impact on the underfloor heatings ability to heat the rooms. I know only adding a few mm but not sure the new tiles would be any nicer if the room was freezing???

[Windmill abu]

A lot of floor and wall tiles are ceramic and as such are good at heat insulation. Having a double layer of them on top of your underfloor heating would make the chances of heat coming through minimal. If only they had known that on the space shuttle.

[Fear ón Srath Bán]

I'd say the tile property 'thermal conductivity' is the key one there NL, the greater that value the lower will be the resistance of the tile to heat transfer from below.

[bridgegael]

dont tile over existing ones,  because sure as hell in three/four years time the woman will be looking a change again,  noiw u are face with lifting two sets of tiles