So if you decide to get a thermostat, (I would) then you need to know about the two types. First the on/off. Generally cheaper. $25-$30 if you search on-line, maybe $40 if you buy at Petco/Petsmart/Big Apple. You set a temp. The thermostat turns on. When it reaches the set temp, it shuts off. (Often the UTH will still heat up a couple degrees more). The UTH temp drops. When it is X degrees below the set temp, the stat kicks on again. So you have a slight variation in temps, which isn't a big deal with corns.
The other type is the proportional thermostat. They are more expensive. Figure $100 and up. They generally have a digital read-out, and many bells and whistles, some of which are really nice, some of which you will probably never need. So you set the temp. The stat turns on, supplying full power. As the temp of the UTH nears the set temp, the stat supplies less and less power, eventually cutting off as the temp is closing in on the set temp, so the UTH doesn't exceed the set temp by more than a couple tenths of a degree. And as the temp drops, the stat comes back on at, say, 10-20% power, when the UTH is just a couple tenths of a degree below the set temp, so it holds the exact temp you set much steadier than an on/off. Does this matter? Not really. But you will also have options that are nice such as matching your thermostat to your thermometer, and will have high/low temp alarms, and all kinds of things.
Let's say you want to be EXTRA careful. You can set up two stats in sequence. First you put in your proportional stat at the temp you want to keep the snakes at. Let's pick 83F. Then you add the back-up stat, an on/off. You set the temp at your fail-safe temp, about three to five degrees higher than the proportional stat. Say 87F. You place both the stat probes together, and plug the proportional stat into the back-up stat. That way, if the proportional stat fails on, (highly unlikely but it could happen) the back-up stat will be controlling the temp, a few degrees higher than ideal, but your snakes won't cook.
A couple things to make your thermostat run safely. Make sure you place the thermostat probe in the center of the UTH, in the viv, under the aspen, and secure it with a blob of aquarium silicone (not duct tape!!!) If the stat probe gets loose, the stat will supply heat to the UTH to try to raise the temp to your setting, but with the probe nowhere near the UTH, the UTH can reach temps of 120-130F! Hot enough to burn the snake. Second, buy a probed thermometer and secure the probe right next to the stat probe. This is how you spot trouble with your thermostat, such as the probe being loose, or with the UTH, such as it dying. (UTHs don't last forever!) Just glance at the temp whenever you pass the viv. You can catch problems early that way.
