i tried a uth on the coolside of a tub... didnt work. still couldnt get my ambient temp above 75 with my thermostats/dimmers off.(no animals in there of course) so im forced to use a tank with lighting to get my ambient temp up. i have a dedicated reptile room but 4 of my geckos cant deal with temps over 80, so heating the room is out. pretty much sucks! wish i could find a way to use the tub. itd be sooo much easier