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In this guide you will learn

In nature, wind is a very important factor for the reproduction of plants. It carries the pollen from the males to the pistils of the female for fertilization. The wind also helps to spread the seeds. After rainfall, the wind will blow the plants dry to protect them from fungi. It also cools your plants off a bit during hot summer days. These are some of the advantages an outdoor grower automatically benefits from, because there’s always a bit of wind.

If you’re growing indoors, you’ll have to create the climate yourself. The heat from the lamps has to be extracted and you need to provide your room with fresh air that’s rich in CO2. The warm and cold air in your grow room has to be mixed well in order to create a constant temperature. Fortunately, there’s proper equipment that can help us to ventilate the grow room and at the same time prevent odor nuisance. In this course I’ll teach you everything you need to know about the airflow in your grow room.

Air exhaust

If you’re growing with fluorescent lighting, you probably don’t have to extract warm air, because these lights don’t get as hot. But if you’re using MH or HPS lamps, the temperature can rise significantly if you’re not extracting any air. A small room of 3x3x6 feet can easily heat up to 120 degrees with a single 600 watt HPS lamp. You definitely need a good extractor for this.

Since warm air rises, it’s best to place your extractor at the top of your room. The warm air with a low CO2 concentration has to be blown out of the grow room. Grow tents have special holes in the ceiling and at the top of the sides to attach the hose of your extractor to. If you’re growing in a closet or room, you have to blow out the processed air through a window or a hole in the door.

Ventilation Air exhaust for marijuana grow
Ventilation air exhaust

It’s useful to attach a carbon filter to your extractor to prevent odor nuisance. All air that leaves the grow room is purified by the carbon filter. Since the filter provides quite a bit of back pressure, you’ll need a 440 CFM extractor for a 600 watt lamp. Read the section How to install my grow room to see how to install an extractor with filter.

Air inlet

Your plants consume large amounts of CO2 from the air. The outside air contains about 350ppm of CO2 on average. If you don’t provide your plants with fresh air, this value will quickly decrease and be at 200ppm after an hour, causing plants to produce less sugars and therefore grow less quickly.

An air inlet is therefore required. An inlet is the same as an extractor, only reversed. Your inlet always needs to have a lower capacity than the extractor, because it could otherwise create positive air pressure, thereby pushing the air out of the room through all cracks, causing odor nuisance. Use an inlet with half the capacity of your extractor. So, use a 440 CFM extractor and an 220 CFM inlet for a 600 watt lamp.

Ventilation Air inlet for marijuana grow
Ventilation air inlet

In addition to CO, an air inlet also blows cold air into the room, lowering the temperature a bit, so your extractor won’t need to use as much capacity. Make sure that you blow the fresh air in from the bottom of the room. This enables the plants to take in CO2 before the air warms, rises and is extracted again.

Air flow

You could install a fan to make sure the fresh air at the bottom of the room mixes with the warm air at the top. Aim the fan between the plants and the lamp, so it can blow away some of the heat the lamp generates and can properly mix the air. I usually place two fans facing each other, so their airflows meet each other in the middle.

A proper airflow also helps to prevent fungi, because they have little chance of nestling somewhere. Bugs and other diseases usually also occur in dead spots. Never aim the fan directly on the plants, because this could cause damage. A nice breeze over the tops of your plants, causing them all to move a bit, is perfect.

Ventilation Air flow for marijuana grow
Ventilation air flow

The plants will create stronger stems by providing them plants with some wind from the very start. The plants defend themselves against hard winds, which they wouldn’t do if there was no airflow. A proper airflow is furthermore necessary to create a constant temperature.

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