Greenstuff
Well-Known Member
I was wondering what size of an passive intake i should use and what size should my exhaust fan be? I'll be using a 400w HPS in a 3x3x7 box
Thanks for help!
Thanks for help!
Passive Intake & Exhaust Fan?
- Thread starter Greenstuff
- Start date
justatoker
New Member
passive intake should be around 3 times the size of the exhaust is what ive heard
justatoker
New Member
I would think 1.5 is minimum.. 3 is optimal. just my opinion. Its jsut what ive heard from other places.
7th1der
Well-Known Member
I only have one intake at the bottom and plan'd on adding another one. Have to see what temps are like once my fan is delivered.
Hairy Bob
Well-Known Member
With HID lighting you want to cycle the air in the room at least once a minute, more ideally, can't have too much ventilation!
You want the passive intake slightly smaller than the exhaust, to create negative pressure in the room and prevent air/odour leaks. I don't know where all this talk of 3x the size has come from...
If you're getting a carbon filter for the exhaust, now or at any point in the future, make sure you uprate the fan so it can cope with the static pressure from that. Inline fans should be roughly doubled, as they really don't like to be held back! If you were getting a squirrel cage or centrifugal fan then an extra 20-30cfm would do, but I don't think one of those would be necessary unless the dimensions you gave were in metres!
You want the passive intake slightly smaller than the exhaust, to create negative pressure in the room and prevent air/odour leaks. I don't know where all this talk of 3x the size has come from...
If you're getting a carbon filter for the exhaust, now or at any point in the future, make sure you uprate the fan so it can cope with the static pressure from that. Inline fans should be roughly doubled, as they really don't like to be held back! If you were getting a squirrel cage or centrifugal fan then an extra 20-30cfm would do, but I don't think one of those would be necessary unless the dimensions you gave were in metres!
justatoker
New Member
sry.. I was mistaken.. I was actually half asleep when I posted.. lol.. A 2:1 ratio is perfect IMHO.. Not 3 times., iunno wtf I was thinking TBH lol.
peace
peace
skippy pb
Well-Known Member
Isn't the intake supposed to be smaller then the exhaust to create a negative pressure, so long as that exhaust is active and the intake passive?
Because this makes the exhaust fan more effective in exchanging the air in your grow box completely.
That what i thought might be wrong though.
Because this makes the exhaust fan more effective in exchanging the air in your grow box completely.
That what i thought might be wrong though.
justatoker
New Member
Yes.. a 2:1 ratio ( exhaust to intake ) is the best way to go IMHO.
skippy pb
Well-Known Member
FUCK... i knew i shouldve read this post but it was the longest one so i was like fuck that. Now i sound like a tool.
justatoker
New Member
na lol.. most of us do that shit. ( dont read every post lol )
Hairy Bob
Well-Known Member
Sorry pal! I do have a tendency to ramble on a bit when I'm stoned. I'll use 50 words where 5 will do...FUCK... i knew i shouldve read this post but it was the longest one so i was like fuck that. Now i sound like a tool.
In summary, I believe it is my fault alone for you not reading my post, and for that I humbly apologize. After all, why should i expect someone on a stoner website to pay a second glance to more than two lines at a time?
Btw, no sarcasm there, not a hint, promise.
Peace
Greenstuff
Well-Known Member
Thanks for the reply's guys.
Would a 4" passive intake and a 6" Exhaust fan work?
Would a 4" passive intake and a 6" Exhaust fan work?
smoke and coke
Well-Known Member
no you want the passive intake slightly larger than the exhaust. a 6" exhaust should have a 7" passive intake.
skippy pb
Well-Known Member
Why?
Also no one here is gunna give you a reliable answer. Unless you already told us the size of the fan and how much air it moved and shit.
I think we have to add in another factor here being the airflow factor and the power of the fan.
Its all about a negative pressure inside the both. If the intake is bigger it defeats the purpose fo the fan.
smoke and coke
Well-Known Member
Detailed vent addition
How do I add ventilation to my grow area details?
Should I place the fan in the exhaust, intake or both?
The fan should be placed in the exhaust, and the intake should be a simple hole (or light trap, if light getting out is a concern).
This type of system is known as an Active Exhaust, Passive Intake System.
Mounting the fan in the exhaust, sucking air out of the room accomplishes a couple of things...
· Since the exhaust is at the top of the area, the fan will suck the hottest air out of the area first.
· The fan is actually lowering the air pressure inside the area. Any incidental pinholes or leaky seams will simply draw air in. If the fan were blowing IN, those pinholes and leaks would allow potentially smelly air OUT.
How big should the passive intake be?
It should be slightly larger than the exhaust. Remember, the volume of air being blown out, will be replaced through the intake. Using a bigger intake hole allows the incoming air to be at a lower velocity (speed), which minimizes mixing up of the air in the area. It will also allow the fan to operate more efficiently.
How big should the fan be?
Fans are rated in either cubic feet (CFM) or cubic meters per minute in North America. In Eurpose, metric fans are rated in m3/hr - cubic metres per hour (m3/hr).
That means a 70CFM fan will move 70 cubic feet of air in one minute.
Your fan should be big enough to move the volume of your area 2 to 3 times every minute. A 70 CFM fan would be adequate for a 35 cubic foot area, and would be optimal for roughly a 23 cubic foot area.
· To figure your area’s cubic volume, multiply (in feet) the length by the width by the height.
What if I have more than one fan? Should I use one to blow air in and one to suck air out?
Not if the object is to provide as much ventilation and cooling as possible.
· If you have two 3-inch diameter fans, and you mount one in the intake, and one in the exhaust, you have a total intake area of one 3-inch hole and a total exhaust area of one 3-inch hole.
· If you use both fans as exhausts, you have TWO 3-inch exhausts and two 3-inch intakes (actually, two 3.3 inch intakes. They should be bigger than the exhausts, remember?).
· Twice as many holes, twice as much airflow.
How do I add ventilation to my grow area details?
Should I place the fan in the exhaust, intake or both?
The fan should be placed in the exhaust, and the intake should be a simple hole (or light trap, if light getting out is a concern).
This type of system is known as an Active Exhaust, Passive Intake System.
Mounting the fan in the exhaust, sucking air out of the room accomplishes a couple of things...
· Since the exhaust is at the top of the area, the fan will suck the hottest air out of the area first.
· The fan is actually lowering the air pressure inside the area. Any incidental pinholes or leaky seams will simply draw air in. If the fan were blowing IN, those pinholes and leaks would allow potentially smelly air OUT.
How big should the passive intake be?
It should be slightly larger than the exhaust. Remember, the volume of air being blown out, will be replaced through the intake. Using a bigger intake hole allows the incoming air to be at a lower velocity (speed), which minimizes mixing up of the air in the area. It will also allow the fan to operate more efficiently.
How big should the fan be?
Fans are rated in either cubic feet (CFM) or cubic meters per minute in North America. In Eurpose, metric fans are rated in m3/hr - cubic metres per hour (m3/hr).
That means a 70CFM fan will move 70 cubic feet of air in one minute.
Your fan should be big enough to move the volume of your area 2 to 3 times every minute. A 70 CFM fan would be adequate for a 35 cubic foot area, and would be optimal for roughly a 23 cubic foot area.
· To figure your area’s cubic volume, multiply (in feet) the length by the width by the height.
What if I have more than one fan? Should I use one to blow air in and one to suck air out?
Not if the object is to provide as much ventilation and cooling as possible.
· If you have two 3-inch diameter fans, and you mount one in the intake, and one in the exhaust, you have a total intake area of one 3-inch hole and a total exhaust area of one 3-inch hole.
· If you use both fans as exhausts, you have TWO 3-inch exhausts and two 3-inch intakes (actually, two 3.3 inch intakes. They should be bigger than the exhausts, remember?).
· Twice as many holes, twice as much airflow.
Greenstuff
Well-Known Member
I think i get it now, passive intake slightly larger than the exhaust. I'm going to go with a 6" passive intake and a 4" exhaust in 3x3x7, how does that sound?
and is the size of a oscillating fan important?
and is the size of a oscillating fan important?
smoke and coke
Well-Known Member
its not the size its how you use it. ooops wrong forum.
it depends on the size room. you want a slight breeze but not blowing directly on them.
