Cfm?

Ok, I did a search but came up with nothing. I have a small grow box about 7.5 cubiic ft. I just got a PC fan that pushes 35 CFM @ 2500 RPM. Would this be enough for this grow box? I think I need to put a hole somewhere for air to come in am I right? Also, where would be the best place to put the fan? (I was thinking top center of the back of the box.) Also for the hole I need to make, I was thinking putting it on the side of the box towards the bottom. How can I light proof these as well?

Thank you.

btt said:

Ok, I did a search but came up with nothing. I have a small grow box about 7.5 cubiic ft. I just got a PC fan that pushes 35 CFM @ 2500 RPM. Would this be enough for this grow box? I think I need to put a hole somewhere for air to come in am I right? Also, where would be the best place to put the fan? (I was thinking top center of the back of the box.) Also for the hole I need to make, I was thinking putting it on the side of the box towards the bottom. How can I light proof these as well?

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You need to change/replace the air in your grow box on average about once every 3 minutes. So to calculate the hourly exchange multiply your total grow space cubic capacity by 20 (60 minutes divided by 3) so that's 7.5 x 20 = 150 cubic feet per hour. Your fan moves 35 cubic feet per minute, converted into hours is 35 x 60 = 2100 cubic feet per hour. So your fan would be more than powerful enough, but 7.5 cubic feet is tiny, that's smaller than a 2 foot by 2 foot by 2 foot box, how are you supposed to grow anything in that? You've either calculated your cubic capacity incorrectly (height x width x depth) or your box is too small.

The fan exhaust should be placed at or near the top of the box so it extracts the hot warm air (hot air rises) and a passive inlet (simple hole) placed near to the bottom of the box so it brings in cooler air. To light proof both, you make a baffle. That's basically a dogleg or 90 degree duct so it can draw or exhaust air out but no light can escape.

OK I lied, it's more around 8 cu. ft. lol. I plan on flowering pretty early 6-8". My grow box is approx. 2ft wide x 1ft deep x 3ft high. Thanks for the reply!