Ventilation
Marijuana Horticulture
by Jorge Cervantes
Fresh air is easy to obtain and inexpensive to maintain – it is as simple as hooking up and placing a proper sized exhaust fan in the most efficient location. An intake vent may be necessary to create a flow of fresh air in the room.
A 10-foot square garden will use from 10 to 50 gallons or more f water every week. Plants transpire (similar to evaporation) most of this water into the air. Every day and night, rapidly growing plants transpire more moisture into the air. If this moisture is left in the grow room, humidity increases to 100 percent, which stifles stomata and causes growth to screech to a halt. It also opens the door for pest and disease attacks. Replace moist air with fresh, dry air, and transpiration increases, stomata function properly, and growth rebounds. A vent fan that extracts air from the grow room is the perfect solution to remove this humid, stale air. Fresh air flows in through an intake vent or with the hep of an intake fan.
Ventilation is as important as water, light, heat, and fertilizer. In many cases, fresh air is even more important. Greenhouses use large ventilation fans. Grow rooms are very similar to greenhouses and should follow their example. Most grow rooms have an easy to use opening, such as a window in which to mount a fan, but security or room location may render it unusable. If no vent opening is available, one will have to be created.
All grow rooms require ventilation. This system could be as simple as an open door or window that supplies and circulates fresh air throughout the room, but open doors and windows can be inconvenient and problematic. Most growers elect to install a vent fan. Some growers need to install an entire ventilation system including ductwork and several fans.
A vent fan pulls air out of a room four time more efficiently than a fan is able to push it out. Vent fans are rated by the amount of air, measured in cubic feet per minute (CFM) or (cubic meters per hour) they can move. The fan should be able to replace the air volume (length x width x height = total volume in cubic feet or meters) of the grow room in less than 5 minutes. Once evacuated, new air is immediately drawn in through an intake vent or an intake fan. Covering the intake vent with fine mesh screen will help exclude pests. An intake fan might be necessary to bring an adequate volume of fresh air into the room quickly. Some rooms have so many crack for air to drift in that they do not need an intake vent.
Do not setup a circulation fan in the room and expect it to vent the area by pushing air out a distant vent. The circulation fan must be very large to adequately increase air pressure and push enough air out a vent to create an exchange of air. A vent fan, on the other hand, is able to change the pressure and exchange the air quickly and efficiently.
Squirrel cage blowers are efficient at moving air but are very loud. Blowers with a balanced, well-oiled wheel run most quietly. Felt or rubber grommets below each foot of the fan will reduce noise caused by vibrations. Run motor at a low RPM t lessen noise.
Inline fans are designed to fit into a duct pipe. The propellers are mounted to increase the airflow quickly, effortlessly, and as quietly as possible. Inline fans are available in quiet, high-quality models that run smoothly.
Propeller or muffin fans with large fan blades expel air through a large opening, and are most efficient and quiet when operated at low RPM. A low moving propeller fan on the ceiling of a grow room will quietly and efficiently move the air.
Hot air rises. Adept growers locate air exit vents in the hottest peak of the room for passive, silent air venting. The larger the diameter of the exhaust ducts, the more air that can travel through them. By installing a biog, sow moving vent fan in this vent, hot stale air is quietly and efficiently evacuated. A fan running at 50 RPM is quieter than one running at 200 RPM. Smart growers install 12-inch ducting and inline fans.
Most often, the vent fan is attached to ducting that directs air out the grow room. Flexible ducting is easier t use than rigid ducting. To install, run the duct the shortest possible distance, and keep curves to a minimum. When turned at more than 30 degrees, much of the air that enters a duct will not exit the other end. Keep the ducting straight and short.