How many CFM for intake/ exhaust in 30 cubic foot room

exactly as the title states


im making a stealth grow box in a dusty garage so i wanted an intake attached to a filter aswell as an exhaust attached to a filter


my room is 22.75 cubic feet, therefore i wanted to have a 10-12 CFM exhaust with a 5-8 CFM intake fan

1) can i attach a carbon filter with a much higher rating than the cfm on my fans (the smallest carbon filter i saw was 150 cfm) ( yes you can! you want a filter with a higher cfm than your fan, this will allow the filter to work more efficiently and increase the useful life of it)


2) if i attach three 10 cfm exhausts and used three 5 cfm intake fans, would the fresh air in my room still cycle every 3 minutes or faster?


3) where can i purchase fans that can go that low in cfm's? (frozencpu.com, i'll use computer fans)

okay im pretty sure theres like 2/3 people that answer in this board so PLEASE just answer one question, MY GROW ROOM IS 22.75 CUBIC FEET

WILL MY ROOM CIRCULATE FRESH AIR EVERY 3-4 MINUTES BY USING;

TWO 3.5cfm exhaust fans (7cfm of exhaust) accompanied with THREE 2cfm active intake fans (6cfm of intake) (22.75/7= 3.25 minutes for air change)

OR

ONE 7cfm exhaust with ONE 6cfm intake


Which setup is better, or i should say, am i able to use setup one or am i stuck with only using setup 2?

any help is GREATLY appreciated

dude you're asking a bunch of potheads to do math calculations. it's gonna take a while. personally I have no clue about air exchange. I use a 400cfm fan turned down to ~50% and just passive intake around the doors of my closet.

ii dP ii said:

dude you're asking a bunch of potheads to do math calculations. it's gonna take a while. personally I have no clue about air exchange. I use a 400cfm fan turned down to ~50% and just passive intake around the doors of my closet.

Click to expand...

both options still cycle the room every 3.25 minutes. but i want to install option 1 so i can get circulation all around my grow room, however, i dont know if i install all these fans that i'll create too much stress on my plants,

the only knowledge i have of ventilation is to keep the intake as far as possible from the exhaust, however, if i just installed one intake and exhaust i think this will deprive my 2 plants of air around the back and sides, i could attach on oscillating fan opposite the intake, but how do i ensure that the fan can 'cyclone' the air in my grow room so that air can go all around my 2 plants?

this is why i wanted to install multiple active intakes to ensure proper circulation.

Here's my bible as far as setting up a room for exchange and cooling.


http://urbangardenmagazine.com/2010/07/planning-your-grow





J

jondamon said:

Here's my bible as far as setting up a room for exchange and cooling.


http://urbangardenmagazine.com/2010/07/planning-your-grow

J

Click to expand...

Thanks! Twas an excellent read but it didn't answer the question of if there can be too much cfm entering and leaving the room. And i was confused as to why you'd multiply 1.25 (exchange in minute) instead of divide, wouldn't you create more stress to your plants by creating a wind tunnel effect?

My room is only 22.75 cubic feet and I want an air exchange every 3 minutes, what size of an exhaust and intake would I need?

Rm Vol = L x W x H = approx cfms needed for 1 minute of air exchange


example: 2x3x5 = 30 cfms needed

Note divide by 3 for 3 minutes = 10 cfms needed

IMO You don't need to over complicate. Buy a cheap bathroom fan from HD or lowes ($14) rated 50 cfms and use for exhaust. All u need for intake is a open vent with filter attached and u will get plenty of air exchange and circulation.

ThePerfectGrow said:

Rm Vol = L x W x H = approx cfms needed for 1 minute of air exchange


example: 2x3x5 = 30 cfms needed

Note divide by 3 for 3 minutes = 10 cfms needed

Click to expand...

I see, so I'm forced into using PC fans to vent my room.

However, would it be possible to use in line fans to intake/exhaust that are rated between 200-400 cfm in a room my size? Or would this cause a wind tunnel effect thus stressing out my plants?

bengali548 said:

Thanks! Twas an excellent read but it didn't answer the question of if there can be too much cfm entering and leaving the room. And i was confused as to why you'd multiply 1.25 (exchange in minute) instead of divide, wouldn't you create more stress to your plants by creating a wind tunnel effect?

My room is only 22.75 cubic feet and I want an air exchange every 3 minutes, what size of an exhaust and intake would I need?

Click to expand...

It actually states that if you are having to exchange your room more than 3x per minute then it can stress plants and AC would be needed.

However no one on this forum can give you a decent answer without knowing what lighting you plan to use.



The reason for the multiply by 1.25 in the link is to allow for restrictions placed on fans by ducting and filters etc.



J

bengali548 said:

I see, so I'm forced into using PC fans to vent my room.

However, would it be possible to use in line fans to intake/exhaust that are rated between 200-400 cfm in a room my size? Or would this cause a wind tunnel effect thus stressing out my plants?

Click to expand...

I've never tried so I can't say but wind tunnel is probably a good assumption.

As jondamon says lots of things such as lighting add to the air exchange formula. good rule of thumb is add 25% to desired air exchange formula to account for lighting and air restrictions like long stretches of winding duct in large grow rooms.

IME with large power cfl's (200-300w versions) they require upwards of 55CFM PC case fans to keep things cool.

I used to use a mother area that was built out of marine boarding and it was 2x3x4ft. So around 20cu ft.

I used to use an AKASA VIPER PWM 88CFM as an exhaust and an AKASA APACHE PWM 55CFM as intake to keep a 200w CFL cool and exchange the room.



J

Here's a link to the building of that box.


https://www.rollitup.org/grow-room-design-setup/368478-mother-box-design-setup.html



J

Sorry, the reason I didn't mention light is because I'll be using a solarstorm 400w led light which doesn't generate too much heat as it is


My temp in summer should reach high 80s to low 90s from what I've read so I won't need to worry about heat management as much, I also plan on getting a dehumidifier+ac module for my grow room

Ideal temp for flowering is 75F.

Especially if you like tight dense buds.


J