Fresh air is inexpensive and easy to find. An exhaust fan is the main tool used to satisfy this need.
In order to have a good flow of air through your growing environment, adequate air circulation and ventilation are necessary. Indoors, fresh air is one of the most commonly overlooked factors in contributing to a plentiful harvest. Experienced gardeners realize the importance of fresh air and take care in setting up proper air movement. Three factors affect air movement: stomata, ventilation, and circulation.
STOMATA are microscopic pores which are located on the undersides of the leaves. These stomata regulate the flow of gasses into and from the plant. These can get clogged with dust, filmy residues, pollen etc... So it is very important to have air movement to keep these pores clean and free.
CIRCULATION if the air is completely still, plants will tend to use all of the C02 next to the leaf surface. When this air is used and no fresh air is forced into its place, dead air space forms stifling the stomata, slowing growth. Air also stratifies with the warm air rising and the cooler air settling towards the bottom of the room.. All of these potential problems are avoided by opening a door or window and installing oscillating fans. Air circulation is important for insect and fungus prevention. Mold spores are present in all growrooms.
VENTILATION an average 10' x 10' foot vegetable garden will use from 10 to 30 gallons of water per week. Where does all this water go? It transpires and evaporates into the air. So basically, gallons of water will be held in the air. If this moisture is left in a small room, the leaves will get limp, transpiration will slow (remember the flow of water through the plant helps keep it erect) and the stomata will be stifled. This moisture mist be replaced with dry air that lets the stomata function properly. A vent fan that pulls air out of the grow room will do the job.
Successful indoor gardeners know that a vent fan is as important as water, light, heat, and fertilizer. In some instances it is more important. All greenhouses have large ventilation fans. It is sometimes said that the person with the most fans wins.
Vent fans are rated by the number of cubic feet of air per minute (cfm) they can replace or move. Buy a fan that will replace the volume (cubic feet) of the grow room air in about 5 minutes or less. The air that is pulled out is immediately replaced by fresh air which is drawn from little cracks under the doors or window sills. If a grow room is sealed tightly then an intake fan will probably be necessary to bring in fresh air.
A vent fan is able to pull air out of a room many times more efficiently that a fan is able to push it out.
To calculate the room size multiply width by height this will give you the total cubic footage of your room for example 10 by 10 by 8 = 800 cubic feet. Remember that you want your fan to exchange the air within 5 minutes so for a room that is 800 cubic feet a fan that is capable of moving 160 cfm is needed.
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