Is it safe to drill a 6" hole into a beam or i-joist for range hood duct?
When I got my first car, my Dad said, “GM builds ‘em, tests ‘em, and tells you how to maintain ‘em...so follow ALL the maintenance rules.”
I think that applies here. They know what their I-joists can withstand. I’d follow it carefully.
The one thing that causes problems seems to be when installers get in a hurry and “eyeball” cuts, etc. id carefully layout the holes and use a SHARP saw. You want it cut perfectly. No tearing of surrounding fibers.
Remember, there is a “safety factor” the manufacturers use and you don’t want to cut into that.
Note: Now you’ve got to be careful of any additional loading (like waterbed, refrigerator, etc.) from the second floor that could affect the manufacturer’s normal design criteria.
For cut timbers there are dozens of things that can go wrong, so I’d get a structural engineer or architect to lay it out, but for I-joists I’d follow their instructions.