View Full Version : Math problem,ventalation part 1

09-03-2010, 10:14 AM
:confused: Can anyone tell me in the faq part of this web site labled ventalation part 1, How they came up with 231 cfm? and can you show how they got that answer?

09-04-2010, 12:56 AM
It's an estimate based on these calcs:

Step 1 – Room Volume
First the volume of the room needs to be calculated. To calculate multiply length x width x height of growing area e.g. A room that is 8' x 8' x 8' will have a volume of 512 cubic feet.

Step 2 – CFM Required
The fan should be able to adequately exchange the air in a grow room once every three minutes. Therefore, 512 cubic feet/3 minutes = 171 cfm. This will be the absolute minimum cfm for exchanging the air in a grow room.

(CFM required for room – step 2) + (CFM required for room – step 2 x 10% (2 air cooled lights)) + (CFM required for room – step 2 x 5% (CO2)) + (CFM required for room – step 2 x 20% (Carbon Filter)) + (Ambient Temperature 0 (Air coming from air-conditioned room)).

The first part is the definitive part, the second part is speculative based on the listed criteria. HID lights obviously add a lot of heat to the room. No clue why Co2 enrichment would add 5%. A carbon filter would obviously restrict flow, hence 20%. And then climate will vary the ambient room temp. The second part seems extremely speculative to me with no citations on where they got the information. You could easily use this info to do your own calculations though.

09-04-2010, 07:30 AM
thanks brbubba