# How to measure exchange of air?



## Bongofury (Jan 18, 2016)

Hello peeps.. I've been thinking again.. I read some peeps like to exchange the air every so many minutes in their grow area. Well, how does one know how many minutes the air is being exchanged. Is there a meter? Again I have googled and can't find the answer.


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## zem (Jan 19, 2016)

calculate the cfm rating on your fan and your growroom cubic feet. cfm=cubic feet per minute


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## Hushpuppy (Jan 19, 2016)

To expound on what Zem just said; You want to exchange the whole volume of air within the growroom or rooms, typically, depending on the size/volume of the rooms from 2x per minute to 1x every 2-3minutes for larger volumes. To determine what you need, you measure your room(s) then You calculate that by multiplying the length x width x height of the room(s) and that will be your total cubic footage. Your fans are rated in cfm= cubic feet per minute. If your total volume is 800cf and you have a fan that moves 430cfm then it will exchange all of the volume of your room 1x every 2min. If you have a room that is only 200cf then the same fan will exchange the entire volume of air 2x every minute or every 30 seconds.


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## Hushpuppy (Jan 19, 2016)

If you have a space that is 2'x4'x8' and you still have that same 430cfm fan and run it on 100%, it will exchange the air in that space roughly 6.5x per minute, which makes it not longer a grow space but a wind tunnel


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## pcduck (Jan 20, 2016)

All that ^^^^^^^ plus you need to subtract some for filter, duct length, and ect.


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