What’s happening growmies, I’m looking for advice on exhaust fan size for my new spot. How do you calculate a setup for a 35-40 sq ft space. I have a 4 inch in there now and it’s not cutting it during first week of flower. Humidity was 72% when I opened the door today. I have another 4inch setup I could throw in there. I’m thinking I will need an 8inch at least. I’m in a basement. Have a dehumidifier running round the clock already. I could add another smaller one closer to grow area also. 3 fans in grow area now. My oh my the stretch has been real on these Colombians! I’m 6’6” and I gotta stand on a 5 gallon bucket to look down for the top view! @OGIncognito @ChittyChittyBangin @Borderryan22 @Spiney_norman @Bonjoyle @DEEPDIVERDAVE @kellydans
I run a 4x4 space with a 6 inch Exhaust fan with variable speed set on medium speed 90 percent of the time. 8 Inch fan should get the job done for you. Your Plants look great 
I use 2 8 in exhausts
I guess I’m looking to get more fresh air in and more air exchange out. My only air in is coming from under the door, 3/4- inch gap. I was hoping to avoid cutting a hole in the wall for more air , but it’s an option. I’m starting to get wet leaves where touching from the humidity inside and I got the 4 inch on full blast. Overall basement humidity is high 50s -60s I’d say. Past few days it’s been 70%ish inside room.
What size space are you in bro?
1 is in a 12x8 and the other is in the 4x8. My flower room dumps into the veg room and the veg room dumps outside
A 8” AC infinity with 69 controller would work just fine that’s what I use in a 4x8. Can you vent to outside with exhaust?
@John7 I’m venting into a soffit that goes like 10 feet across and into another closet. I don’t think venting outdoors is an option right now.
That’s pretty sweet set up!
Probably not enough intake area to let your fan move as much as it could. A more powerful fan would just make it worse in terms of efficiency. (More intake area would improve efficiency.)
The soffit itself may be small enough to also be restrictive, depending on the fan itself & the cross-sectional area. You said its 10’ long.
You can bench flow your fan & make a flow gauge at the same time, then reinstall & check for losses on your gauge easily enough.
But where does the air from the closet go? Is it an enclosed space to where it can’t move from there?
That’s what I’m thinking an 8inch with filter and I’ll Punch a 6-8inch hole down low on drywall to bring more air in.
The soffit is pretty wide 2-3 ft and just goes into closet , I insulated and fire caulked any openings inside the room, so it’s pretty sealed. I don’t think any exhaust air is coming back into the room. I could open the door to closet and let it back into basement, or just contain it somewhat.
If you’re exhausting into the closet & it’s also a sealed area, then the fan is not going to do much of anything, even if the intake side was completely unrestricted.
On a flow map you’d be at max pressure & zero air flow, even with an unrestricted intake side.
Basically a similar problem to the intake side, where the only intake area is the space below the door.
You’re going to want to provide more area on both sides until the fan can move as much air as it can.
That being said, a 4" fan probably won’t be enough for that space & you’ll probably need to go to a more powerful fan, but it might be worth it to get the 4" flowing some air first, just to see. If you only need it to control RH, it might possibly be enough, depending. Probably most likely not enough for hot air temps.
AC-Infinity T8’s Move air quietly, from 227*CFM up to 806.9
AC-Infinity Cloudline Controller 69P+ handles it well.
Just know that those numbers are from a fan with no restrictions, & only a change in power. The more useful metric to know before you buy is seeing a ‘pressure vs. flow’ map, which ACI doesn’t provide for any of their fans. Either way, unless I’m misunderstanding his setup, he’d still be at basically 0 CFM at 2867 RPM until he gives the air somewhere to come from & somewhere to go. He won’t hit the rated max flow number unless the airflow through the fan is still unrestricted on both sides once installed. Adding restrictions starts to move the CFM number down, even at full power. Sometimes restrictions are unavoidable, but you want to minimize them to get as close to max flow as possible. The more restrictions you add, the lower the CFM number goes. (Although hybrid fan types like the S8 do usually have a plateau in the middle of the flow map somewhere, but even that falls off too. We could see that if they showed us ‘pressure vs flow’ maps for their fans.)
I just ordered the ACI 8” setup. I drilled an 8” hole on the one side wall of grow room and stuck a fan in front of hole . I also opened the exhaust dump closet door to allow for no restrictions. I think I’ll be in good shape come Monday when fan arrives. Appreciate y’all @DEEPDIVERDAVE @PhotoFinisH @ChittyChittyBangin @kellydans @John7