If you have a UTH, you must regulate it either with a dimmer or a thermostat (the latter being preffered). I have used both and they both suit my needs, although the thermostat is most convenient.
Here is the dimmer you can get at the home depot: http://www.homedepot.com/webapp/wcs/...10000003+90401
You just plug your UTH into it and use the dial to get the UTH to the proper temp.
Here is a thermostat that I have used and has worked well for me. It is nothing fancy though. http://www.reptilesupply.com/product.php?products_id=75
Keep in mind you MUST use a thermometer with a probe to measure the temperature of the UTH to make sure it is right. The little stick on dial things are un-reliable and usually off by as much as 10 degrees.
