Thanks for the replies. I think I'll just go with the 8" Max-Fan and try it out, have a speed controller if I need to dial it down. Rather go overkill on the fan then not go big enough.

I do have the fans for my old setup, but they're only 4". I'd try out your suggestion bigsby, but wouldn't the 8" to 4" reduction make quite a big difference in the math? Thanks for the light trap tip too. I've always used 180 degree turns thinking it was necessary.

When I get this put together would anyone be interested in a DIY guide to putting together a sealed room with top drip to waste system for a couple 4 x 4 tables? Not sure if there's anything like that posted on here atm. I know I wish I had a guide to follow when I put my first one together.