That is pretty good- I had not tried it with glass. Rate of climb was pretty slow and steady and not much of anything will combust at that temp. You can hold your hand on it. Of course the animals would be parked at the other end of the tub- this is a point I make often to people. Do not over do it on the heat, you will kill animals faster with heat than cold if they have no way to get off of it. Always allow for this and have a gradient!

I actually tested a few elements in a much more "hard core" way. I used a piece of 1" think fiberglass insulation on the top and the bottom of the element. Had very similar results out of both elements.