Ok there are three types of house hold t-stats mercury switches (older styles) bi-metal springs and digital. They all basically do the same when the temp dips below the set point the switch triggers a relay that starts the heating system. The problem is you either have to place the whole T-stat where you want it in the enclosure... very impractical or you could modify a digital by moving the resistive sensor to a probe. The problem with that is the resistive sensor works be the changing resistance to a small electrical current the addition of a wire alters the resistance and the calibration (which isn't great to start with goes out the window.) The prices of house hold t-stats around me any way range from 50$ to 300$. That means a t-stat designed for controlling a heat pad (greenhouse hydrofarm) is less cash and a reptile designed one is in the range of 100$ which is not that much more. The last issue is accuracy the reptile designed ones are spec'd at 1ºF +/- I have 3 herpstat pros and a ND and II. I can tell you that they are all with in 0.6 of correct (measured with a platinum tipped RTD traceable thermometer) And most are better than 0.5ºF A ranco johnson or hydrofarm are spec'd at 2ºF +/- a household spring type is 5ºF +/- most keepers find that unacceptable for temps that you could set at 92º and have 97º.
I personally believe in using a product designed to do what you are attempting to use it for as well. The Herpstat, Helix, VE series, Ecocene, and a couple of others have been designed from the ground up and not adapted from else's where. They are my first choice, I also understand that small run electronics are not going to be cheap. There are a few that have been adapted to our purpose for years, johnson, ranco and hydrofarm is the new comer but they seem to work reasonably well in lower voltage applications.
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