Skiploader, I am sure that you have had constancy with your rheostats for years I am 100 percent sure of that. You have also stated the crux of the rheostat issue. Constant ambient temps, they are unable to do more than deliver X (say 30%) power that will raise x (say 10 degrees) over ambient. That is great I am also confident in saying you have multiple rack systems and a dedicated room to you collection. That space has fully regulated ambient heating. You don't have the issues that exist if you have a small collection, no rack system (that creates a micro climate) in a living space. My house and the area I live has rapid and large temperature changes outside (26ºC 46.8ºF change in 24 hours) The interior temperature also changes with it. Where my snakes are I have ambient temperature variations from 84-70ºF. A rheostat cannot work under these conditions. My herpstat keeps the hot side 91º constant and my cool side from thermo-spill shifts a few degrees up and down from a base line of 80.9. When I was testing a set up with a rheostat I was getting hot side variations of ten degrees up and down and 15 on the cool side. That is unacceptable. I actualy and switching soon (next full cleaning day) to twin heating systems controlled by a herpstat pro One for the cool side one for the hot side. so I can have a comfortable work room again!