CFM fans and tents

Thread starter #1
Hello everyone I'm struggling to get my head round how much air, and how often needs to be extracted from the tent That i have on ordered

Please could someone link me the forum post or be kind enough To explain the equation to me.

Tent dim are 240x120x200
I think my fan is 175m3/he ????

Cheers everyone
How often do you run fans mate or is it constant
Run that can same timer as the HiD

Then I have 2 6" fans pointing at the tube left and right helping cool the air directly around the outside of the tube..

Plus the 6" ducting is sucking from the highest part of the tent..

And I have just 4" ducting feeding cold air from a window with no fan..

Always negative pressure


Well-Known Member
hello headlaaa!

i run a 1500 cfm tordado acoustic extraction fan that also does a 1.2x2.4m tent aswell as a 1.2x1.2m tent on a y piece.

i dont use no where near 1500cfm in both, if you wanted you could get a 1000 cfm tornado or similar.

i use a fan speed control aswel with the fan which is perfect for getting the right temps you want!

my extraction fan runs 1hr after the lights go off, but my small fans inside run 24/7.

never noticed a difference running extraction 24/7.

quite cheap to and well worth it!

good luck with your grow.
Based on your measurements for both the tent and your fan, I'll assume you're in Europe somewhere. If so, is that 175M3/H rating correct? If it is, you'll want a larger fan.

You've got a growing area of roughly 5.76m3 (about 204 cubic feet) and your fan cycles at around 2.91m3/minute (roughly 102.75 cubic feet / minute).

The idea is to completely evacuate / exchange the air inside the tent every minute, so at a bare minimum you'll need a fan that provides 345.6m3/H (or 204cfm).
Assuming you'll want to run a carbon filter with your setup as well, you'll have to increase your fan power by at least 25% to compensate for the extra resistance (most people use a 1.33 multiplier to be safe) so that would mean getting a 460m3/H fan (or 271cfm).

You'll likely end up with something a little more powerful than you need and use a fan controller to reduce the power as needed, but if you're pretty close to the numbers it isn't required / worth it. Just make sure you maintain a slight negative pressure (the tent walls will have a slightly "sucked in" look) and you'll be good.

If you're concerned about heat buildup more than anything else, bear in mind that the fan is a big part of temperature management, but there are a LOT of other factors, not the least of which is lighting system and ambient temperature of the air you're drawing into the tent as well.