I would spend a little more and get one better and easier then a rheostat. With Eheostats you are going to being adjusting the temps all the time. Every time the room temp changes so will you hot spot. Get you a thermostat. I use a Ranco, they are cheap and simple. You can get them many different places, just do a search. I have even seen them on ebay for about $30. They are $75 plus shipping at this site,

http://www.rancoetc.com/ranco-etc111...a81bc19b06d95c

If money is not a factor, get you a Helix!!