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.