Quote Originally Posted by giaach View Post
Actually I messed around with a rheostat and found that while it doesn't allow as much power to the UTH. It will eventually get to the hottest temp which in my experience is around 115. Basically by dimming the UTH it just takes longer for it to get hot but still gets to its highest temp. SOOO I would def suggest getting a thermostat. There's a nice sticky in Husbandry that shows a glass tank set-up.
That is not true. A rheostat doesn't slow the transfer of power to the UTH, it cuts it. It essentially is a manual form of a proportional thermostat. Theoretically, if you have the rheostat switch set directly in the middle, the device should be using half the power it normally would. A rheostat controls how much power the device is allowed to use.

What your seeing is probably your ambient temps rising throughout the day, which in turn will cause the heat/temperature to increase. In this case you would have to adjust the rheostat to compensate for the higher ambient temperatures.