It sounds like that's because of the heat tape trying to do too much work (too much temp dif between the room and rack) I bet the fact that it doesn't touch the tub makes it harder to retain heat as well. Airflow = lower temp. I had to crank mine until I realized that just wasn't safe. I started keeping my room at 79-81 and the temps stabilized perfectly. I now have my Herpstat set at 93.8 degrees and it does a perfect job keeping temps stable at 90-91 on my hotside. Have you tried setting your proportional setting up to Hi1 or Hi2? You got to remember that Flexwatt is like 8 watts a foot for 4". That just isn't going to heat a room full of air when the temps fall under a certain amount.

Regards,

B