Quote Originally Posted by kitedemon View Post
The manufacturer recommends an air space so I would suggest that that would be prudent as they know their product better than anyone else does. http://www.calorique.com/pdf/PetWarmingElements.pdf

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this set up inverted would be fine too.
This link is for the heat "sink", not the FW if i read it right. Any unregulated heat source is NEVER a good idea. There is no space required if a reliable thermostat is used. This link also suggests connecting the FW directly to underside of enclosure. Something I would never do.

Before I switched to tubs, I actually mounted my FW on a cheap ceramic tile, so the heating element had no contact with the floor (or wooden stand).
As a precaution, I used the little rubber/silicone cabinet/drawer bumpers available in any hardware store, on the corners of the tile. This allowed enough space to allow the thermostat probe to fit under the enclosure without the enclosure sitting right on the probe itself. In this set-up, even with a stat failure, fire was nearly impossible.