CFM calculation?

Discussion in 'Growing Marijuana Indoors' started by Noam_Chomsky, Jun 17, 2006.

  1. If a grow room is 4'X4X6'7", then the fan CFM should be 107.2 or greater. Am I correct in this calculation?

    Meaning I would need a exhaust fan that rates 107.2 or above?
  2. Forgot to include other things as well.

    400 Watt HPS lighting. Although Ballast will be out of growbox. Would I still count 400 Watts since the ballast is not in the grow room?

  3. depends on how hot it is in your area. You might need to move 2 or 3x that much if you think heat will be an issue
  4. You have slightly over-calculated your volume -- 6'7" is not the same thing as 6.7' but close enough, your volume is about 105 cu ft. are making an unfound assumption that you should exchange the air in your grow space at a rate of once per minute. I am more familiar with a 3x turnover per minute, which would dictate a fan of at least 415cfm for that space. That also assumes adequate intake and exhaust.

    This is the standard for ventilation only. When you add in the need to control temps there is no rule of thumb because there are too many variables at play. I'm not sure what you mean by "counting" 400 watts -- your light will throw off some additional heat, and if you are worried about heat (and having the ballast out of the grow space is a good move from that standpoint) then the only measurement that matters is a thermometer.
  5. Thanks for the input toasty.

    Yea i freak up on the CFM calculation. Divide that 79 inches by 12 then calculate right?

    Also I guess I'm assuming a correlation between temperatures and airflow.

    On the grow box it says: The roof area comes with an attachment to mount your exhaust fan and filter, plus a 6-inch outlet sleeve for ducting the fan exhaust! Ventilation holes are located at the bottom of the grow closet - by utilizing an exhaust fan and charcoal filter at the top, the Homebox gives you a chimney drafting effect to prevent odors while providing needed air circulation.

    Does these seem sufficient for a 415CFM fan?

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