Quote Originally Posted by lord jackel View Post
But using this same logic doesn't this mean that you really don't need a back-up at all since even if the thermostat is stuck open it cannot push enough current to cause an issue?

A Rheostat by design lowers the amount of power getting through it...so if it blocks 10% then is blocks 10% of 1000watts or 10watts - the difference is still huge. This is the same reason why the actual temp in the tub fluctuates with the ambient temp of the room when using a rheostat cause it cannot compensate for increase or decreases in temp.
Absolutely correct and why I stated that while the circuit would work with the rheostat, I still do not recommend it! You would to clamp a UTH at a certain wattage you would have to calculate its resistance through the use of the Rated Voltage and Wattage of the UTH. Then calculate a resistance to put in series with that that would create a situation in which only a given voltage that would keep the wattage from going past a given point. At this point you would use a fixed type resister in series with the UTH to accomplish this. Still not the way I would do it, but it is a way to accomplish a means! But to figure out what wattage you want the heater to run at you would need to get into transfering Watts to BTU's and calculating volume of the enclosure and a whole bunch of other variables such as temp of room the enclosure is in, which in most houses will not stay constant throughout the year. Back to constantly making adjustments on your rheostat. Not fun!