How many CFM?

M

mightymouse12

Active Member
i am building a new grow box tomorrow since my wife wants the closet back. it's going to be 2.5' wide, 2' deep, and 6' tall. my last few plants have already bean veging for a while now and will be switched to flower as soon as the box is done. i'll be flowering with a 400w HPS. and was wondering how many cfm my exhaust fan should be? thanks for any advice.
 
P@ssw0rd

P@ssw0rd

New Member
well assuming your not using a carbon filter, in that small of a space with a 400 i would highly recommend a air cooled reflector. but 2.5x2x6=30 Cubic feet, so assuming you want to change the air 4 times an hour [i think thats right but its late and im high]thats 4x30=120 so get a fan of at least 120 cfm, but you can always go higher, especially if you plan to use a cheap inline type fan.
Good luck
 
2kstyle

2kstyle

Well-Known Member
P@ssw0rd said:
well assuming your not using a carbon filter, in that small of a space with a 400 i would highly recommend a air cooled reflector. but 2.5x2x6=30 Cubic feet, so assuming you want to change the air 4 times an hour [i think thats right but its late and im high]thats 4x30=120 so get a fan of at least 120 cfm, but you can always go higher, especially if you plan to use a cheap inline type fan.
Good luck
Click to expand...

what if he was using a carbon filter, how much more would the cfm be for his situation? I have a similar amount of cubic feet to him that's why. thanks
 
P@ssw0rd

P@ssw0rd

New Member
hard to say, I'm far from an expert, If you bought the filter get a fan that matches the rated cfm of the filter. If you built it, i can really help much, sorry. but i built my own filter from plans on the RIU boards, and i use a 350 cfm squirrel cage fan [and a diy cooltube] in a space approx 4'x2'x6, with a 400watt hps, keeps it nice and cool and smell free. But a squirrel cage or centrifugal fan works WAY better then an inline when it comes to pulling through a filter, they just can't handle the back pressure of the filter. good for intake fans, or cooling a cool tube i guess. let me know if i can help anymore.
good luck:peace::joint:
 
email468

email468

Well-Known Member
if the exhaust fan is properly rated for the room (CFM is equal to or greater than three times the cubic feet of the grow area) and the carbon filter is rated for the fan, you can expect proper efficiency and longevity from your fan and ditto for the carbon filter.
 
User24

User24

Well-Known Member
cfm = 3x the cubic feet seems high, in a 10x10x8 you would need a 2400 cfm fan.

i think maybe its cfm/3, for air exchange every 3 minutes then a 10x10x8 would only need a 260+ cfm fan
 
bigballin007

bigballin007

New Member
Fresh air is essential for healthy plant growth, especially in an indoor environment. Intake and exhaust fans are necessary to exchange air in the garden area, as well as to provide relief from excess heat and/or humidity. Circulation fans are also necessary to strengthen plant stems and to prevent stagnant air from building up around leaves. Fan capacity is expressed in CFM (cubic feet per minute) of air movement. To exchange air effectively, it should be done in 5 minutes or less. To choose the right fan(s) for your space, multiply the garden area's length x width x height. Divide this cubic volume by 5 to determine the MINIMUM CFM of air movement. In other words, your fan should be able to remove or exchange the entire volume of air in your garden area in 5 minutes or less.
168 cfm fan or so that will change the air out every 5.6 min
 
email468

email468

Well-Known Member
User24 said:
cfm = 3x the cubic feet seems high, in a 10x10x8 you would need a 2400 cfm fan.

i think maybe its cfm/3, for air exchange every 3 minutes then a 10x10x8 would only need a 260+ cfm fan
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The more fresh air the better. Your calculation was correct - if you are using a single fan to exhaust that large a room, then you'd want it rated at 2400 CFM.

though for that size room, I'd recommend two but you could get away with one FanTech FKD14 or if you really want to get things rolling a FanTech FKD14XL.

Can you get away with less? Sure can. in fact, as little as one time every minute would be adequate.

My source for this info is: Grow Great Marijuana by Logan Edwards
 
2kstyle

2kstyle

Well-Known Member
P@ssw0rd said:
hard to say, I'm far from an expert, If you bought the filter get a fan that matches the rated cfm of the filter. If you built it, i can really help much, sorry. but i built my own filter from plans on the RIU boards, and i use a 350 cfm squirrel cage fan [and a diy cooltube] in a space approx 4'x2'x6, with a 400watt hps, keeps it nice and cool and smell free. But a squirrel cage or centrifugal fan works WAY better then an inline when it comes to pulling through a filter, they just can't handle the back pressure of the filter. good for intake fans, or cooling a cool tube i guess. let me know if i can help anymore.
good luck:peace::joint:
Click to expand...

Thanks for the help so far. I got a dillema where I don't want to spend to much, but I was researching and found a inline can exhaust fan, which is rated at 188 CFM from still air ( In-Line Booster Fan, 6" ) or should I get a bigger fan, like a 265 squirrel fan. I'm trying to keep the elec bill down, and the noise factor down. Currently I have a 50 CFM computer fan cooling the light, so that is the fan I'm going to be replacing. thanks
 
P@ssw0rd

P@ssw0rd

New Member
the fan you linked two is going to be LOUD. So if noise is a concern avoid it, however if you really want one they can be found at lowes, Home DePot etc for considerably cheaper then that. Believe it or not some of the best fan deals i have seen is on amazon.com Check it out for yourself, just do a search on amazon for "hydrofarm fans" They would be much better, greater true cfm, and if you bought a large enough one you would be able to add a carbon filter later on w/o needing to buy a new fan. Good luck
 
email468

email468

Well-Known Member
P@ssw0rd said:
the fan you linked two is going to be LOUD. So if noise is a concern avoid it, however if you really want one they can be found at lowes, Home DePot etc for considerably cheaper then that. Believe it or not some of the best fan deals i have seen is on amazon.com Check it out for yourself, just do a search on amazon for "hydrofarm fans" They would be much better, greater true cfm, and if you bought a large enough one you would be able to add a carbon filter later on w/o needing to buy a new fan. Good luck
Click to expand...
good catch!
 
2kstyle

2kstyle

Well-Known Member
P@ssw0rd said:
the fan you linked two is going to be LOUD. So if noise is a concern avoid it, however if you really want one they can be found at lowes, Home DePot etc for considerably cheaper then that. Believe it or not some of the best fan deals i have seen is on amazon.com Check it out for yourself, just do a search on amazon for "hydrofarm fans" They would be much better, greater true cfm, and if you bought a large enough one you would be able to add a carbon filter later on w/o needing to buy a new fan. Good luck
Click to expand...

thanks did you hear of the Dayton squirrel fan brand? I was just wondering what is better, Hydrofarm or Dayton squirrel fans?
 
Maccabee

Maccabee

Well-Known Member
Hydrofarm and Dayton are both fine. I picked up another Hydrofarm the other day, and it's working well as expected although for some reason this new unit is much noisier than my old one, and there are some holes in the weld around the exhaust coupling so I may exchange it for another unit. Hopefully they didn't have a bad lot shipped out of the factory or anything like that.
 
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