Hi hp hope everyone is well today , i jsut had a quick question ......i jsut wondered if you bought a 6 inch exuast fan , i know you can buy clips , that allow you to reduce the duct size from 6 inch to a 4 inch , so you can use 4 inch duct on a 6 inch exuast , if that makes sence , well my question is could i hook up a 4 inch exuast to the 4 inch duct , thats attached to a 6 inch exuast fan ?

That's exactly right. You get a reducer for 6in to 4in, and then you can use the 4in ducting.

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No point in mentioning these bats I thought, poor bastard will see them soon enough.

Remember that Fans (real turbine fans) are rated at 100' of straight pipe (snap ducting, not flex) ducting equal to the fans size. So every foot of ducting you have in there that is 4" when the fan is 6", subtracts well more than 1 foot from your 100'. So running a short distance of 4" is OK, but if you run a lot, your fan will not be operating at the rated CFM. I actually like to run bigger ducting than my fans use.

sorry was in a rush when i first wrote the first post , kinda missed the major point to my question lol , would i be able to put a 4inch carbon filter with a 6 inch fan , using a reducer for the 6 inch exuast fan to a 4 inch duct

Chances are a 4" carbon filter doesn't need the airflow a 6" fan will give it. Meaning you would be better off using that fan for exhaust intake, and get a cheaper 4" for your carbon filter.


If you already have your exhaust/intake hooked up, and have an extra 6" fan, yes it will work. Probably really well, since you are giving the filter more airflow than it needs.