I have a 3.5 x 3.5 x 8 foot closet which im planning on converting to a grow room, my problem at this stage is with the venting.
There is already a small hole in the wall leading directly outside, the hole is about 3/4 and inch with about 4-5 inches of space between the inside and outside of the wall. Is this size hole big enough to get a working vent tube through? or will i have to deface the wall a little. Also if anyone had a site explaining how to set up a cheap vent system handy that would be great too.
Cheers
Each fan has a rating that tells you how many cubic feet of air per minute (CFM) it will move. When dealing with above average temperatures you will want your fan to exchange the grow room air 3-5 times in one minute, so for a room that is 40 cubic feet, a fan that is capable of moving 120-200 cfm (cubic feet per minute) is recommended. If you only want to replace depleted levels of co2 and are growing in a closet using fluorescents, one room change per five minutes (divide room size by 5) will be adequate.
To calculate your room size, multiply Width by Length by Height, this will give you the CFM rating required for one room change per minute.
Air that’s exhausted will be replaced by fresh air, which is drawn from
Passive Intakes-
located opposite the exhaust at the floor of your grow room (Recommended for closet grows) or
forced in using another blower (recommended for larger grow rooms).
For internal circulation oscillating fans are In my opinion the most efficient devices for circulating air in a room. The gentle back and forth sway of the fan is very beneficial for the developing plants. These fans tend to keep anaerobic moulds down by constantly freshening any potentially stagnant air. Home improvement centres carry a large array of various types and styles of air-moving fans, there are wall-mounted styles available and most are relatively inexpensive.
NOTE: To convert CFM to CMH use the folowing formula CFM X 0.03 X 60 = CMH
so you have 3.5x3.5x8 = 98 cubic feet.
if your going to use cfl's and heat is not an issue then you can get away with a smaller exhaust. according to above divide 98 cubic feet by 5 would give you 20 cfm for 1 room change every 5 minutes. i would get at least a 100cfm. exhaust.
if you are going to use a MH or HPS light and heat will be an issue you will need to change the room air 3 to 5 times a minute. for 98 cubic feet you would need 294 to 490 cfm exhaust.
that 3/4 inch hole is quite small.
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.
sorry for the long post as far as going cheap on your ventilation is a crap shoot. if you dont have enough ventilation your plants will suffer and not produce. most that go cheap in the start find out that they need to upgrade and get better exhaust fan.
