I built this welding booth a couple of years ago. Should of built it decades earlier. I bought a variable speed Fantech (https://www.fantech.net/) exhaust fan. I picked one and called them for tech support. They were great and I ended up with the next larger size. I exhaust through a 6 inch pipe I used to use for an oil furnace that I don't use anymore. But honestly, it does not pull real hard. It does work, but I still wear a respirator whenever I weld. I'm anal.

I would call them, tell them what you want to do and get some feedback...........