Ventilation, air exchange !

Hi growers. This is my first grow. I need information about CFM. I have 12cm PC fan for exhaust which is 112,13 m3/h so it will be 1,87 m3/min ... I will put behind fan carbon filter, so I think it will lose about 20% of CFM. And it will be about 1,5 m3/min. My grow room is about 1,5 m3 ... Is this fan not to big? Cause I read that air must change one time per 5 minutes... Is it true? And I need help with intake, can I put 100 m3/h fan for intake, with some filter before it, or it will make positive pressure?!?... I have in my grow room one HPS 250w bulb and 3 CFL each 23w 2700k just for light mixing... I hope someone will help me. And sorry for my english, and for meters not feets...

http://botanical.com/hydro/air/calculating_fan_requirements.html

Before everybody starts chiming in with some good info and a lot of bullshit, go read and learn knowledge for a lifetime and not just for pot. No worries on metrics. There are converters online free for that.

My motto - "Go big to grow big". That applies to AIR, containers and light in that order! If they can't exchange gasses what the hell good does a huge light array or Wango Bango Super Nutrients do?

And when this fellow comes along to tell you to plant in teeny tiny containers because "pot won't grow up until its roots touch the sides of the container" just know he is incorrect. Well meaning but totally wrong. Put them in the biggest container your grow area will handle. Screw repeated transplantings and the subsequent shock following each one. Cut to the chase, boys.

I don't really get it. I make everything like in formula, add all stuff, and my minimum CFM is 0.63 m3/3min but my PC fan which is 12cm x 12cm does 1.87 m3/min ... So I need fan which is 3 times smaller than mine, it sounds very weird. About temperature I can't do any math 'cause I don't know what temperature make my fan ...

Ok lets say in m3 ...

L 1.1 x W 0.85 x H 1.5 = 1.40m3 ... If air must exchange every 3 minutes so it will be 1.40/3 so 0.46m3/min ... Add 20% for carbon filter and 15% for HPS without ventilation, and we got 0.63m3/min... But My fan does 1.87m3/min... This what I've got...

I have about 2 months old AK48 feminized, 5 pots each 15L ... One is big about 60cm and ready to flower, others is about 40cm and ready for flowering to. They now is in my sun house but it is getting cold outside so I made grow room for them, I have everything done but don't have info about correct ventilation

Without your temps, projected at least, you cannot figure the size and this leads to the problems. The reason I simplified it by saying go big to grow big. Buy the biggest sonofabitch fan you can fit in there! You cannot move too much air while you can easily move too little.

you talk about air circulating fan inside grow room or about exhaust or intake fan? Tomorrow I will turn all lights on and watch what temperature will it be only with circulating air fan inside grow room, no exhaust and no intake... Will see the numbers...

Just measure my grow room... L 1.30m x W 0.86m x H 1.50m = 1.68m3 / 3 = 0.56m3/min (CFM)

CFM = (0.56 x 20%) + (0.56 x 15%) = 0.756m3/min X 3 = 2.268m3 each 3 minutes ...

Exhaust PC fan 112.13m3/hour = 112.13 / 60 = 1.868m3/min x 3 = 5.60m3 each 3 minutes... Am I right?

My PC fan http://www.soselectronic.com/?str=371&artnum=45381&name=sunon-dp201at-2122hbt-dp201at-2122hbt-gn

I measure all in feets and my result was 60 CFM ... My PC fan is 67/80 ... But what does it mean 67/80???? I think my fan will be alright

All you can do is see. Fans do not cool air. They move air. They can help bring a grow area to the ambient (surrounding room) temp but that is all. They can only do that by moving large amounts of used air so heated air is not allowed to remain.

ErikBL said:

I don't really get it. I make everything like in formula, add all stuff, and my minimum CFM is 0.63 m3/3min but my PC fan which is 12cm x 12cm does 1.87 m3/min ... So I need fan which is 3 times smaller than mine, it sounds very weird. About temperature I can't do any math 'cause I don't know what temperature make my fan ...

Ok lets say in m3 ...

L 1.1 x W 0.85 x H 1.5 = 1.40m3 ... If air must exchange every 3 minutes so it will be 1.40/3 so 0.46m3/min ... Add 20% for carbon filter and 15% for HPS without ventilation, and we got 0.63m3/min... But My fan does 1.87m3/min... This what I've got...

Click to expand...

DUDE. STOP worrying about size of the fans.
I think what harley is trying to get you to understand, is just because you read the numbers on the box, which will indicate maximum performance of that fan under optimal controlled test conditions, do not stick that number in your head as written in stone.
Think of it like making a pot of spaghetti. You grab a small pot, just big enough to some for yourself. Then the doorbell rings, and you've got company for dinner...... Now you have to get a larger pot in order to cook more.
Granted, this is easier than going out and buying a bigger fan in 3 months when you decide your math was bad and you need more air flow.
Also, I have no idea what you are talking about you can't do math about fan and temperature, the fan does not cool or heat the air. it MOVES the air.

Thanks dude... Will try now what I have and than make conclusions about size of fan