i rigged up a stanley blower to a 6" vent for exhaust. i have a 7" passive intake. both exhaust and intake have two 90 degree elbows to block light.
i turn on the blower and it feels like there is a fan in the intake but there isnt, its not needed.
this is in the growfaq
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.
