CFM fan size & carbon filter ?

guynbama40 · Mar 11, 2014

8' x 6' x 9' closet grow setup, 432 ( edited -cubic ft. ) sq. ft. - 6 inch passive intake with 4 inch can fan H.O 155 cfm, fan mounted in attic, exhausted thru roof in pvc pipe (no filter) used for my first cfl grow (2 plants). which turned out ok with very little odor. Well, I have upgraded to a air cooled hood, 600 hps digital dimmable. (3) strain grow Big Bang (GH), Grapefruit Krush (ET), Pineapple Skunk (Humboldt) Botanicare coco bricks, perlite, cal mag plus, superthrive (1 drop) GH 3 part, going into week 4 from seed and already the skunk is smelly. I would appreciate recommendations on carbon filter and fan size and how I can utilize what I have setup now ? Here are a few photos BB and PS (day 24) GK (day 15) Thanks

photo (1) krush (2) skunk (3) big bang

rickymac21 · Mar 11, 2014

I think you mean 432 cubic ft. But your going to need a much bigger fan if you want to scrub the air properly. Although some strains odor are minimum, they say the fan should scrub air 4 or 5 times a minute to be safe.

So you have 432 cu ft. Multiply that by 4 and thats roughly 1700. So to scrub the air 4 times per minute youd,need a 1700 cfm fan. Obviously thats a lot, and ho,estly i never agreed with that knowledge. Or i guess i should say just not necessary.

If your fan you have already is 155 cfm, i would buy a 400-1000 cfm fan. The bigger the better obviously.

As for setting it up , i would have the smaller fan at the very,end of the duct in the attic. Then id have the larger fan,directly in front of the hood. So both fans are pulling from the hood and carvon filter.
The filter size will depend on the total cfm of your fans. If you get a 600 cfm fan, add 155 for the one you have, so 755 cfm. Youll want a filter that can handle thag easily. Otherwise the filter wont be,scrubbing properly.

Ask questions if that was too much and didnt make sense. I have a tendency of rambling.

jondamon · Mar 11, 2014

rickymac21 said:
I think you mean 432 cubic ft. But your going to need a much bigger fan if you want to scrub the air properly. Although some strains odor are minimum, they say the fan should scrub air 4 or 5 times a minute to be safe.

So you have 432 cu ft. Multiply that by 4 and thats roughly 1700. So to scrub the air 4 times per minute youd,need a 1700 cfm fan. Obviously thats a lot, and ho,estly i never agreed with that knowledge. Or i guess i should say just not necessary.

If your fan you have already is 155 cfm, i would buy a 400-1000 cfm fan. The bigger the better obviously.

As for setting it up , i would have the smaller fan at the very,end of the duct in the attic. Then id have the larger fan,directly in front of the hood. So both fans are pulling from the hood and carvon filter.
The filter size will depend on the total cfm of your fans. If you get a 600 cfm fan, add 155 for the one you have, so 755 cfm. Youll want a filter that can handle thag easily. Otherwise the filter wont be,scrubbing properly.

Ask questions if that was too much and didnt make sense. I have a tendency of rambling.

It is recommended to exchange air once per minute up to a maximum of 3x per minute before you need to use an AC.

There are restrictions that must be allowed for when sizing a fan for a grow room.

Initially you start with your cubic area.

432CFM for one air exchange per minute.

Add 25% for the restriction a carbon filter adds. 108cfm extra. Total 540CFM.

Add 15% for an open reflector 600-1000w. 65CFM extra. Total 605CFM.

You need to look at duct lengths and bends.
Any bend that's at 90 degrees restricts airflow by 20%. Either add the 20% or remove the bend.

Every 10FT of ducting reduces efficiency by 5%.

Keep duct lengths short, or add the 5%.

J

guynbama40 · Mar 11, 2014

Thanks a lot rickymac21 and jondamon, yes ricky I did mean cubic feet, my bad, well that answered my question, guess a little carbon filter research is next. One more thing, wouldn't a 400 to 600 CFM fan be extremely loud in the closet? and about setting up another fan with filter, would it be placed like this

carbon filter - fan - minimal ducting - hood - ducting thru room roof - already installed 155 cfm fan ?? out 4 inch exhaust pvc pipe already installed ?

one other issue can I reduce the 6 inch ducting to 4 inch to exhaust the air out ?

Thanks again guys

Ou8aCracker2 · Mar 11, 2014

Restricting the ducting will add more pressure losses,so no.

guynbama40 · Mar 11, 2014

Thanks Cracker, so I can shut down the 4 inch exhaust fan set up and exhaust the 6" out of my attic via the attic fan opening ?

CFM fan size & carbon filter ?

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