I am installing a kitchen fan about 9' away from the nearest external wall. The wall there is very narrow and all I can fit there is a dryer type vent that works with 4" round pipe. Also, my spacing behind the framing along those 9' allows me only about 4" of space.
Can I exhaust a kitchen fan through a 4" round pipe across 9' linear with only one 90° turn? I'm guessing kitchen fan ventilation is subject to more scrutiny because the fumes contain oils that settle along the pipe, presenting a cloggage (carbon monoxide) and fire hazards.
Best Answer
Sure, you could exhaust a jet engine through a 4" pipe but the problem is the velocity of the air. As the size decreases the velocity increases for any given cubic feet per minute rate of exhaust.
So, what you have to do is calculate the velocity of the air through a 4" pipe given the CFM of the fan. And then will that velocity cause an objectionable noise. Most bathroom fans are connected through 4" round ducts and go up to 900 CFM or so?
What size fan do you want to use? What will the velocity of the air be? What is the recommended velocity?