Good ventilation accomplishes several things:
1. Provides continual CO2 (the main component of air) which plants need in abundance for good growth. In commercial greenhouses, air drawn in one end by large fans may have nearly all the CO2 exhausted by the time it exits the other end.
2. Vents out moisture transpired by the plants. This may amount to gallons of water per day.
3. Reduces heat buildup from artificial lights or sunlight. Depending on the size of the space and wattage of light(s), this may eliminate heat buildup.
A good rule of thumb is to completely exchange the air in a growing area every 5 minutes. A commercial grade blower is used. Place the blower so air is drawn from the top of the space where the air is hottest and vented out. Size it by the required CFM (see application guide below). Blowers are rated by the amount of air they move in CFM (Cubic Feet per Minute). Bear in mind that with any duct attached, a blower will only move about 1/2 the rated CFM.
PHP Code:
Dimensions of space Total volume of space Required CFM
(assuming 8' ceiling) (in cubic feet) for 5 minute air exchange(CFM=Volume / 5)
4' x 4'........................128...................26
5' x 5'........................200...................40
6' x 6'........................288...................58
7' x 7'........................392...................79
8' x 8'........................512...................103
9' x 9'........................648...................130
10' x 10....................800...................160
(thats 160 for the 10 x 10. wouldn't let me put it there
)