Recommend Mat Size?

I'm upgrading one of my guys to a 45 inch wooden viv pretty soon, and I'm going to buy a new heat mat with it. Should I stick with an 11 inch or 17 inch (length) mat? I'm worried 17 would be too big.

17 inch is still less than 1/3 the length of the new cage you are building so it should be fine.

Are you planning on sandwiching between glass or tile or is the bottom a material that is thermally conductive? Wood (Not melamine but actual wood/plywood) tends to be not the best for UTHs. you need to get a fully water resistant one that can be seated under tile or glass for use inside the wooden enclosure. This will make it no different than placing it on the outside pane of glass on the bottom of a glass tank. the main difference is you cannot use heat tape or non sealed heat pads as that would be a short and fire hazard.

However... Look into a radiant heat panel instead. Will offer far better options than the UTH in a wooden enclosure if you, like me, are uncomfortable placing a UTH inside an enclosure.

Edit: I suppose plexiglass would work to sandwich ;)

Thanks for the advice- though I'm not building a new one, I'm going to be getting this: https://www.reptiles.swelluk.com/viv...lge-walnut-45/

His current tank is the same make, just smaller, and has so far been just fine with the UTH inside, but I'll make sure to look into it just in case :)