Ben, the idea is to set your heating up so even if your thermostat fails and its on full bore it still wont get hot enough to fry your snake.
What I do is set my heating up so its adequate even without a thermostat, then have the thermostat as a fail safe and fine tuning tool.
Josh, I use 25w 4.3m heat cords, and I use the FB17 Freedom Breeder rack. I really can't see how, if the thermostat fails, that my snakes will ever get cooked.
25w distributed over 4.3m means about 15 degree+ on ambient temps. If ambient temps get to say 30 in my house, that's 45 degrees, right on the heat cord, not in the tubs, which are about 3 degrees cooler. The 50w heat cords are a different story and you need to be careful with those. If you're that way, I'd use two thermostats, use a dimmer stat for the heat cord, and then use a standard On/Off thermostat as backup, set the backup at the ambient temp where the heat cord would overheat if the dimming thermostat failed, say at 25 degrees, and you should be fine.
The heat panels are double insulated and also protected by a reasonably thick metal place which is what the rack tubs actually sit on. The heat mats don't get terribly hot, about 40 degrees from memory. In fact I think my 25w heat cords get hotter than those panels, and they will not fry my snake. I have air conditioning in summer, so that keeps the max temps at my house at 31 degrees.
Seriously, I'd be much, much, much more concerned about the A/C system failure. Now that WOULD fry my snakes. It gets pretty hot, and inside it can be up to 5-6 degrees hotter than outside. Let's just say if it got to 40 degrees outside and my A/C failed I'd be up sheet creek in a barbwire canoe.
To the point, I am going to get my A/C looked at (or maybe even get a new one) where if the power fails it will automatically restart. Right now, it can't do that. So either I can get a small resistor changed in the A/C system that will enable the auto-restart or get a new unit. I will ask around. Daikin seem like a good brand, and at $1500 it isn't a bad option. I'm also going to get a new gas hot water system installed so I'll probably do it all at once, before the end of the year.
They were just in this enclosure overnight until i could get them into their 4ft, not that they seemed overly concerned!
