yeah, definatly dont put it on the inside, because i put mine on the outside there is not as accurate. However, thats why i put another digital thermometer on the inside. For example, if i set the T-stat to a perfect 91 then it would probably be around 88 in the hotspot. Which i would see from the digital thermometer. So i jack the T-stat up to 94 and it hits 91. Also it probaly dpsnt matter what heat pad if they both hit the required hot spot temp. And herpstats are allways very nice and will be much easier then a cheap dimmer.