I really like my cool tube on the 400w. It have a 4" fan at 172cfm running same distance into attic with a carbon filter at the end.
I would say you need a 6" or 8" fan, but it depends on the size of your room. Here is a calculator for figuring fan CFMs.
http://www.littlegreenhouse.com/fan-calc.shtml
or you can do it the hard way...
1.)
Convert all inches into feet
Quote:
inches ÷ 12 = feet
38÷12=3.16'ft W (rounded up to 3.2)
28÷12=2.3'ft D (rounded up to 2.4)
42÷12=3.5'ft H
2.)
Find the volume, feet cubed, of your cab.
Quote:
multiply Width × Depth × Height
W × D × H = feet cubed
3.2'ftW × 2.4'ftD × 3.5'ftH = 26.88'ft3
3.)
Find for Exchange CFM rate. We want to echange the volume of the cab 4 to 5 times a minute. I will use the value of 5.
Quote:
feet cubed × 5 = Exchange CFM
26.88'ft3 × 5 = 134.4CFM
4.)
Find for Additional Electrical Cooling CFM rate. Add all the watts of all equipment inside the cab.
Quote:
total watts of all equipment ÷ 4 = Additional Electrical Cooling CFM
250 watt light + 50 watt additional equipment = 300 Total Watts
300 Total Watts ÷ 4 = 75 AEC CFM
5.)
Add the two CFM rates to get Total CFM
Quote:
Exchange CFM + AEC CFM = Total CFM
134.4 Exchnage CFM + 75 AEC CFM = 209.4 CFM
6.)
Find the CFH (Cubic Feet per Hour) from the Total CFM rate.
Quote:
Total CFM × 60 = CFH
209.4 Total CFM × 60 = 12564 CFH
7.)
Find for the amount of carbon needed for the filter.
Quote:
CFH × grams per foot of activated carbon (0.36) = total amount of carbon required.
12564 CFH × 0.36g per ft = 4523.04g
8.)
Divide the amount (in grams) of total carbon by the length to yield the radius quotient. This is done with 2.6cm thickness as a constant.