If you are brewing ales, putting carboy inside of water filled cooler is a great, cheap way of controlling temps. I have 2 carboys in my large rectangle mash tun right now. I just check the cooler water temp and the liquid crystal thermometers on the sides of the carboys twice a day.
For example, I just brewed yesterday so fermentation is cranking right now. The water in the cooler is 64 degrees, but the beer is at 68 degrees. As the fermentation slows I can increase the water temp in the cooler to maintain 68 degrees. It's as simple as draining a bit of the water from the cooler and adding a little hotter or cooler water to adjust temps...no electricity costs, mash tun (in my case) doubles as a temperature control device.
This is all done in my basement which varies in temps throughout the year anywhere from 64 degrees to 72 degrees depending on the weather outside. Keeping my ales at 68 degrees and not allowing higher temps has made my beer very consistent and clean.
''Once, I thought I was wrong, but I was mistaken'' (Read that somewhere, just loved it. Sorry if I stole it...consider it a compliment)
''I don't allow work during drinking hours''