I just had this problem too. I got a reostat and I wasted my money on it. I had gotten away with not using a any type of controling device by putting more or less air space between the tub and the uth. But I had to change this every few hours and it was really a pain to keep the temeratures right. I finally said screw this and ordered a ranco and flexwatt from rich at reptile basics. It is on its way now and will really make keeping my snakes much easier and safer. I could recommend getting a ranco. They don't cost as much as some of the proportional thermostats and if your room temeratures fluctuate at all you are going to have a ton of trouble keeping the temps right with a dimmer or reostat.