The only reason you would need a second UTH is if you keep your house colder than about 75-77 and the ambient temp inside the tub doesn't hold. I would suggest starting off with one UTH and see how it goes. I keep my house temps cooler, but I use a space heater in the snake room to keep the ambient temps in there up. I also use an oscillating fan to circulate the air around the tubs which helps keep the humidity stable. Also, when you go to Wal-Mart to get the tub, you should consider getting a soldering iron. They cost about $6 and will make punching the holes so much easier and quicker, unless you already have a drill and want to use that...