Before you do anything, run the system up and measure the actual floor surface temperature. Once it's stabilised, if it's around 35 degrees C (95F), you are already at or near the limit. A higher floor temperature, created in an attempt to boost performance, might make walking on the floor in bare feet a distinctly unpleasant experience, if not dangerous to babies and pets. Depending on the cover material over the heater element, its temperature may already be close to the limit too, and it may even have a thermostat buried with it, which will negate all your plans. I'll let my betters here comment on the electrical implications, but my gut feeling is that this is a bad idea.
Alan
PS. Noticed you stated a 'tiled floor'. You can expect a maximum performance of around 10W per sq foot, (100W/M2) on ceramic/cement flooring, less on wood/plastic.
[This message has been edited by Alan Belson (edited 08-06-2005).]
