Not quite sure how going from an on/off T-stat to proportional/dimming T-stat would cause a swing in humidity. Temps, sure. I'm using a Hydrofarm on my BP cage atm and I have it set to 91F. It turns on at 88.8F and turns off at 91.0F but gets up to 91.7F which is understandable with an off/on T-stat. My humidity is stays at 56-60%. But like I said, since a UTH doesn't heat the air, I cant see how it would affect your humidity that much. I got a Herpstat 1 on my red tail cage and its the same. I wont argue though that they are really nice. I'm just debating whether I want another Herpstat 1 redline or regular or a Herpstat 2 redline or regular or just go for a Herpstat 4 to run both my boa and BP cage and have wiggle room for anything else later. Anyways grats on the Herpstat, they are really nice.