+1 to everyone about the substrate. A thermostat is the safest way to regulate a UTH...not piling on substrate. Mine all bury under their substrate and lay directly on the glass. I suggest aspen over the carpet. I've never used it but I've heard after being washed a few times it gets kind of gross...not worth the money IMO. Aspen is easy to spot clean and easy to spot messes, holds temps well (I only use about 1/4 - 1/2 inch of aspen).