8 inch intake / 12 inch exhaust

where do most people intake their air from? If outside air is the only option and one lives in the north, what to do? Perhaps use flex ducting and direct incoming air towards ceiling? 24ft by 16ft room.

Before intake, you say 8" fan with a 12" exhaust. Why? Increasing tubing or pipe sizes reduces the speed of the moving air. Cold air piped into the ceiling area is going to immediately sink. Intake from anywhere, including just outside your grow room. It's the odor in the exhausted air most are concerned with.

Decrease your pipe or tubing diameters as the run goes longer to keep the velocity of your air up. Don't increase it.

Too much neg pressure doing it this way. You would want to go 8" exhaust and 12" intake if the same amount of length and turns.

If cold air hits the ceiling (or anything) in a warm room, if its cold enough air, it will cool the object below the dew point. Condensation will build, and you'll have moisture on that spot.

- Jiji

I went with 8 and 12 inch fans because I need to move that many CFM. Many websites have led me to believe I want to change the air every 60 seconds. I know this will not be possible (outside temp average about 36 degress), but how close can I get?

outside temps 36 degress centrgrade use a Split Air Conditioning and use a 5" carbon filter/fan exhaust and a 4" fan intake

hang a 6" carbon filter/fan to the room to reduce the oder in late flower, keeping the room cool is the most important thing 20-30c

outside temps 36 degress fahrenheit use a 5" carbon filter/fan exhaust and a 4" intake fan ( run it when the lights on )

hang a carbon filter/fan to the room to reduce the oder flower
use a heater to keep the room warn when the lights off

when you start a new grow getting the room environment perfect is a waste of time and money, you just want the environment so you can grow a few healthy plants and pull a good yeild.

intake air aimed at the floor and exhaust fan/carbon filter as high as you can
(heat rises)

couple of fans to mix the air is alway good

Dogfish907 said:

Many websites have led me to believe I want to change the air every 60 seconds. I know this will not be possible (outside temp average about 36 degress), but how close can I get?

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This seems to be a common mantra about grow rooms. But I don't buy it. Whats it based on? The only answers people have make no sense.

If you exchange air, you should be exchanging air according to your temp or possibly humidity(which would be less likely). Plants use very little co2 in a room. So if your constantly moving air, it doesn't matter how much the CO2 isn't going to change. If you don't believe me, get a CO2 monitor.

Now if your not constantly exchanging air during lights on, but only cycles, it depends on plant matter and volume of room, and building construction etc. But even then its not that important as long as air gets exchanged periodically.

- Jiji

Thank you farmgang. That makes sense. Jorge Cervantes, and a couple other youtube sites are where i got that info. I will just let the 12 and 8 inch fans regulate room temp and humidity accordingly. Perhaps use some flex ducting to ensure cold air is not blowing directly on crop?

Farmgang,
current vent plan has 12inch exhaust and 8 inch intake. Is this backwards? Is my local grow shop guy giving me bad info?

No its not backwards.

I always like to do passive intake if I can.

A 12 inch fan moves a lot of air. You might not need that intake fan.

- Jiji

jijiandfarmgang said:

No its not backwards.

I always like to do passive intake if I can.

A 12 inch fan moves a lot of air. You might not need that intake fan.

- Jiji

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A 12" fan does move a lot of air. To balance that with a passive intake youd need close to a 24" opening. Or a couple of 12s or so.... and so on.

That comes from my experience with an 8" exhaust anyway....nearly collapsed my space.....lol

Gquebed said:

A 12" fan does move a lot of air. To balance that with a passive intake youd need close to a 24" opening. Or a couple of 12s or so.... and so on.

That comes from my experience with an 8" exhaust anyway....nearly collapsed my space.....lol

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I only have a 4" intake fan when the lights on and a 6" exhaust fan runs 24 hours ( I will never have an oder problem even with the door open but my room is soil and the walls are painted)

but thats a very good point gquebed, if you have black and taped to the wall or using a cheap tent this will cause a fire, just a mater of time !!