Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

dust to prolong the life of the activated charcoal filter. Whether the intake is passive or brought in by a fan, use a filter for incoming air to minimize pollutants in the grow room.

Ozone can severely damage foliage. This is what it does to foliage.

Charcoal filters remove fragrance and pollen from the air. The model shown above has a half-inch outer filter that encases porous ducting surrounded by activated charcoal. These filters are efficient until humidity climbs beyond 60 percent, at which point moisture-filled charcoal fails to absorb.
    Check with filter manufacturers or retailers about venting specifications for your grow area. A more powerful exhaust fan will be necessary to draw an adequate volume of air through the activated charcoal filter. An adequate airflow is imperative to keep a high CO 2 content in the grow room air.
Setting Up the Vent Fan - Step-by-Step
    Step One: Figure the total volume of the grow room. Length × width × height = total volume. For example, a grow room that is 10 × 10 × 8 feet (21.5 m 2 ) has a total volume of 800 cubic feet (10 × 10 × 8 feet = 800 cubic feet) (21.5 m 2 ). A room measuring 4 × 5 × 2 meters has a total volume of 40 cubic meters.
    Step Two: Use a vent fan that will remove the total volume of air in the room in less than five minutes. Buy a fan that can easily be mounted on the wall or inline in a duct pipe. Quality inline fans move much air and make very little noise. It’s worth spending the extra money on an “in line” fan. Small rooms can use a fan that can be attached to a flexible 4-inch (12 cm) dryer hose. Many stores sell special ducting to connect highspeed squirrel cage fans with the 4-inch (12 cm) ducting.
    Step Three: Place the fan high on a wall or near the ceiling of the grow room so it vents off hot, humid air.
    Step Four: If possible, cut a hole in the wall, and secure the fan in place over the hole. Most locations require special installation. See: Steps 5-9 below.
    Step Five: To place a fan in a window, cut a 0.5-inch (1.5 mm) piece of plywood to fit the windowsill. Cover window with a lightproof dark-colored paint or similar covering. Mount the fan near the top of the plywood so it vents air out of the grow room. Secure the plywood and fan in the windowsill with sheet rock screws. Open the window from the bottom.
    Step Six: Another option to make a lightproof vent is to use 4-inch (12 cm) flexible dryer ducting. Vent the hose outdoors, and attach a small squirrel cage fan to the other end of the ducting. Make sure there is an airtight connection between the fan and hose by using a large hose clamp or duct tape. Stretch the flexible ducting so it is as smooth as possible inside. Irregular interior surfaces cause air turbulence and seriously diminish airflow.

An activated charcoal filter is attached to a vent fan. The air is cleaned before leaving the grow room.
    Step Seven: Another option is to vent the air up the chimney or into the attic where light leakage and odor are seldom a problem. If using the chimney for a vent, first clean out the excess ash and creosote. Tie a chain to a rope. Lower the chain down the chimney, banging and knocking all debris inside to the bottom. There should be a door at the bottom to remove the debris. This door is also used as the exhaust vent.

Can carbon filters are available in many sizes and are a popular brand.
    Step Eight: Attach the fan to a thermostat/humidistat or other temperature/humidity monitor/control device to vent hot, humid air outside. Set the temperature on 75°F (24°C) and the humidity on 55 percent in flowering rooms and 60 to 65 percent invegetative rooms. Most control devices have wiring instructions. More sophisticated controllers have built-in electrical outlets, and the peripherals are simply plugged into them.

Air is deodorized by an ozone generator that is inside this ducting.
    Step Nine: Or attach the vent fan to a timer and run it for a specific length of time. This is the method used with CO 2 enrichment. Set the fan to turn on and vent out used CO 2 -depleted air just before new CO 2 -rich air is injected.

Air flow and volume are diminished when they turn corners.

This grower uses insulated ducting to dampen noise and vibrations caused by moving air.

A small fan placed in a window box removes smelly air 24 hours a day.

Turning air around a corner keeps grow room light from signaling passersby.

Here is a charcoal filter without the outer dust filter. The inline fan