Perfect guide to finding your CFM Requirement.

This is a formula with 4 variables; A, B, C, and D.
Assign each variable the value based on this guide, then put those numbers into the formula down
at the bottom.

-== A ==-
A is equal to your total Cubic Feet  WxDxH   for this example we are going to punch in 4x4x6.5
A common dimention to the growing popular grow mylar tents.
4x4x6.5 = 104 Cubic feet Divided by 3
A=104 /  "rounded to 35"
If your grow is a TENT, divide A by 3
If your grow is a "Closet or ROOM" divide A by 2
If your grow is a larger then a small bedroom or walk in closet, do not divide A
A = (104 / 3 )
A = 35
With active intake you can move up that formula one step.  2 becomes 3, etc.
Although I would use active intake and not move up a step, its always good to have a bit more.


-== B ==-
For each non-tube/air cooled HID light add 1.10 to 1.15 (250 watt - 1000 watt respectfully)
   (Tube cooled lights do NOT heat the room as much so)
    For each air cooled/tubed HID add 1.05
for this example we will say a 600 watter, not tubed. going to go the high end of 1.15
for 100-250 i would use 1.10  for 400 up i would just use 1.15, for 1000 you could do 1.17
Add each one up together for your grow room.
We have just the one 600 watter so
B = 1.15


-== C ==-
The value of C starts at C = 1.00
If your using CO2 add .05
If your using a Carbon scrubber add .20
For our example, No CO2 and a carbon scrubber is used, so 1.00+.20
C = C + CO2 + Carbon;                            "Sorry for the C++ syntax"

C = 1.20


-== D ==-
The value of D is either one of these 3
If your outside temps and humidity is normal for your "plant" then the value is excluded from the formula or use 0
If your temp is higher like California, as example, its value is 1.20
If your temp is high, while being humid. the value is 1.40
This example is normal
D=0

A + (A x B) + (A x C) + (A x D) = Minimum CFM for your room

35 + (35 x 1.15) + (35 x 1.20) + (35 x 0) <--- Yes, 35 x 0 = 0, thats right!
35 + 40.25 + 42 + 0
= 117.25 CFM required for this room "Bare minimum"

In a hot climate with humidity that would be
35 + 40.25 +42 + 49
=166.25 CFM

Remember this is the bare minimum and i suggest you follow this precisely then add 20%
Adding active intake will also boost CFM on the exhaust fan.

Active intake should be directly across on an angle from the exhaust
Exhaust should always be at the top where air in hottest.
This will pull intake up and across your space, through all your plants before being exited again.
Use screens on the rooms venting to prevent bugs.


Post below for comments or suggestions.