Is this tray suitable for electric underfloor heating to go onto?
This tray is suitable underfloor heating usage. However because it's a good insulator it can limit the effect underfloor heating provides if it's installed under the tray. It's best to install it on top of the tray, under the tiles.
To do that you need to take into consideration that there is 15 mm vertical frame, which is fixed and cannot be adjusted. Your material installed on top of the tray (including tiles) can go slightly above the frame but it's not recommended to have it several mm above. Ideally it's flushed with the drain, for an instance you would need 6 mm UHF mat, 8 mm tiles and 1 mm for tile adhesive.
David 020 7193 0953