by Jorge Cervantes
Air Ventilation
Install air exit vents in the hottest part of the room – usually the highest point – for passive, silent air venting. The larger the diameter of the exhaust ducts, the more air that moves out. Airflow is usually inadequate with just an air vent. Add an exhaust fan to make the air move faster out the air vent and increase airflow in the room.
A fresh-air intake vent is necessary to create a flow of fresh air into the room. The vent can be in the form of cracks in the grow room walls, a space under the door, or an actual louvered vent. it must allow enough air to enter the grow room so there is an adequate flow of fresh air into the room.
Locate intake vents near the floor so they bring in cooler air. An exhaust fan vented outdoors that pulls new air through the vent usually creates a sufficient flow of air. If passive airflow through the vent is inadequate, attach a fan to draw air into the room.
A slight vacuum inside the room that keeps the door closed generally provides the perfect scenario. The ratio of 1:4 will give the room a little negative pressure and keep the door closed.
Fresh air entering the room should be the same temperature as air within the room so that plants do not suffer temperature stress. Cover the intake vent with fine mesh silkscreen to help exclude pests.
Grow spaces must have an exhaust vent or an extraction fan. The air must change in the room every 1-5 minutes. Air in small grow spaces should change every minute. A vent fan pulls air out of a rom 4 times more efficiently than a fan is able to push it out.
Axial fans are quiet and move air efficiently when properly installed. Attach the fan to a rheostat (fader switch) to control the speed, or to a thermostat. Turn fans down to the point at which they make virtually no noise and will still keep the room a cl 75F during the day and 70F at night.
Exhaust or extraction fans are rated in cubic feet per minute (cfm) or cubic meters per hour or air volume they can move. The fan should be able to replace the air volume (length x width x height = total volume) of the grow room in 1-5 minutes.