I was curious how quickly should your fans be able to completely exchange the air in a room? If I am going to have rooms that are about 1300 cu ft, would a fan that moves 600-800 cfm be effective or would I want it to be exchanged in about a minute or less? And would having a smaller fan on at a low speed bringing air in 15 minutes of every hour be a wise choice?
If exchanging air is what you want to do in a large room like that, then you will need a fan that does 1000 cfm+. General rule of thumb is to completely exchange the air every minute. With a decently sized room like that you could also consider going completely sealed with AC and CO2
You need to calculate your CFM (cubic feet per minute) of the room, L x W x H.
Once you know that, you can look at the specs on different fans. Liked mentioned above, exchanging the air every 1-3 minutes is the goal.
Two important tips:
1- Buy a stronger fan than you need. When you run these fans on lower speeds, you get less noise and vibrations, but you also have the chance to turn it up if needed in extreme cases. You also have a fan that can move with you into a larger or new grow area.
2- The length of your ducting will reduce efficiency of the fan. Efficiency lowers even more when you start putting bends or turns in the ducting.
If you bought a fan that is just enough for the CFM of the grow area, but then you add ducting and make a few turns, the fan will no longer be adequate for your needs.
Thanks, great info. I am essentially making 3 underground grow rooms out of 3 conex’s to help control the drastic cold temps of Montana in the middle of a forest. I was wondering about the length of ducts and whatnot.
oh yeah, if you have an intake fan that is bringing in more air than is going out at the moment, you create “positive” pressure, which will blow internal air out through the seems. This air does not go through the carbon scrubber and could put the smell of your grow in the air, which is not good for stealth. That is why you want to run “negative” pressure.
Stealth is a non issue because if anyone that I don’t want to smell it can, they will have 2 Caucasian Sheperd’s to deal with. So just use exhaust fans when needed for temp or humidity should suffice?