will my 6" fan be able to take in air from a 4" sewer roof vent pipe.

will my 6" fan be able to suck enough air through the 4 inch pipe coming through my roof to cool 4 x 600w lights.

i am going to use a reducer to increase from the solid 4" inlet pipe to a 6" flexi acoustic duct to the lights.

i dont really have any choice i just hope it can draw in enough air to keep my lights cool.

You really want to suck air from a shit pipe?

I would think not. I used to run 1 6 inch fan per 2 lights with a straight run. having a bend and reduction plus 4 lights, going to be hot.
Sidd

uh, why would you want to suck air in from a sewer pipe? That idea is all kinds of bad. Also, I wouldn't do it. It's difficult to explain but messing around with vent pipes for toilets can end really, really bad. In short, you could fuck up the drain system and have a shitty mess(literally)

drill a hole in the floor and suck air from the crawl space. Much better idea.

most likely not. with that much heat your going to need a 8 inch at least and maybe 2 of them. even at 1 or 2 600 watt i would think you would still have cooling issues going from a 6 inch to a 4 inch like that.