Quote Originally Posted by ChrisBowsman View Post
If the rheostat was going BEFORE the thermostat, I'd agree with you. However, it is AFTER, so it won't affect the amount of anything the thermostat sees.

The t-stat will be set to provide enough juice to heat the UTH to 92 degrees. If the r-stat is set to allow the passage of enough to heat it to 95, there is no problem.
The rheostat is a resister which limits current by using power! This means it will require the proportional T-stat to push more power to achieve the proper temps. This could result in overloading the proportional T-stat as most are only rated for between 400 Watts to 500 Watts. That equals a little less/over 4 amps at 120 Volts AC. In order to create a limiting point you will have to create a situation that limits based on its max Wattage. Running at max wattage is taxing on SCR's and transistors as they run hotter. This reduces the life of the proportional T-stat and also will create problems with the overload circuitry shutting down and no heat being created until it is reset. The only way I would do it is use a On/Off T-stat before the proportional controller if a back up was needed!