Ok so I have a 20 gal high ISO in my room. I've had it there for about 3 months I assume. I didn't have any more stands, but needed to ISO some of the crabs. So I put it on top of a carpet in my room. My room has carpeting, and then I put it on top of a rug about the same size of the tank.
The UTH was under that tank - and plugged in for most of the time.
At the crab convention my Dad calls me saying he smells something strange in my room. I don't think much of it - and when I get home I'm not sure what it is. All the crabs were fine. (note there haven't been any crabs in the 20gal for 3 weeks now)
So since this tank has just been taking up space in my room, I lift it up today to move it downstairs. I pull it up a little and see I still had the UTH plugged in - I un plug in. When I lift it up I have to rip it off my rug because it was sticking too it!
It had burned a whole thru the rug! And that burn went thru to the main carpet.

SO if you have any tanks with UTH under the tank, be sure to check them!! If I did not choose to move this tank today it could have got worse, and my room could have gone up in flames. The tank is right near my bed, and a fire could easily spread onto the bed sheets of mine. I don't want to wake up and be on fire...
I've learned my lesson my main carpet has the burnt stain on it so I won't forget this. So remember please be safe while crabbing!!