Thank you. One is also considerably smaller than the other, so I really don't believe it will cover the whole bottom. Like I said it's just temporary until I get a larger enclosure. Do you think my ambient temp will be OK with just the UTH's? That's the only reason I want to use the other UTH on the 20L, so I can move my CHE to my 40, since my ambient is too low in that one. My other temps are good on both, it's just that darn ambient temp!