Hi, I'm new here
I am setting up a small workshop in my shed, and have a question about duct size for ventilation - the hood I've got has a 7" duct opening. As most inline fans are widely available in 6" and 8" versions, I'm wondering how to join 6" or 8" ducting to the hood. If I bought an 8" inline fan and 8" ducting, what would happen to the CFMs if I add a reducer to 7" right where the ducting joins the hood? Will that kill the power of the fan? Should I go with a less powerful 6" fan with 6" ducting instead, and add a duct increaser right where the ducting joins the hood to fit the 7" opening? I'd rather do the first option if it lets the more powerful fan still do its thing, but if by reducing the opening to 7" I'm dropping the CFMs of the fan, then maybe I should just buy a smaller fan and go with 6" ducting?
Ducting will be minimal - 2-3 feet of ducting above the hood plus the fan plus a 90 degree elbow to vent outside.
Thanks for any insights!