FYI, you aren't going to be able to bump ambient temps up with a UTH. You might be able to gain a couple of degrees but nothing substantial. That is the drawback of tub setups, or rack setups because there is no way to really bump ambient temps up without making adjustments to the room. In a nutshell whatever temp the room is the tub is going to be. 75 degress really isn't a problem IMO for these guys. Thats what my room averages during the cold season. Also you said something about keeping your room at 90 degrees which is kind of crazy lol. The most IMO is low 80's. You figure in the wild these guys are in rodent dens all day, and aren't out basking like lizards do. I think people stress ambient temps too much with balls. Also, I notice some of mine like it a little cooler. My one ball always stays on the cool end for the most part. And all my temps are thermostat controlled so its not too hot. So shoot for mid 70's if its a problem.