Question about inline fans (6" fan w/ 4" duct)

If I get a 250 CFM 6" inline fan, put 6" to 4" reducers on it, and used it with my 4" ducts, how much would the CFM drop? I have a 4" inline now. It's a little weak. It's rated at 80 CFM.

Depends on the size of the room and its enviroment. For a simple 3x3x7 grow room i would use a 6" vortex fan thats rated around 450 or so. 80 or 100 or even 200 is going to keep the temps down where you want them 72-76

The 80 CFM 4" isn't enough. Even if the 6" reduced down dose not pull as much air as it would on 6" ducts it should be better than the 4". I'm going to get a vortex or similar when I pick up my HPS next month. Right now I don't have the funds. 6" inline and reducers are $35.

quick Q, did u get the $24 or whatever 6in one from htg? I recently got that one, and found out it was actually rated at like 160cfm BUT 250cfm if used with a booster fan, basically ANOTHER fan inline with it. But on to UR Q.... The drop in cfm, depends a lot on how much ducting ur running. Far as I know, there's no magic formula for the actual drop in cfm in different situations. Just gotta tweak the system till it's workin.

Yeah, I was going to get the 6" from HTG. I work about a mile from their store. Maybe I'll run my 4" and a 6" at the same time until I get a vortex. Thanks for the info.

Try a 6" valueline from ebay