How to organize a proper airflow when growing indoors?

How to organize a proper airflow when growing indoors?

Organizing decent airflow and ventilation around your plant is the primary question to be addressed when one decides to grow indoors. Improper airflow in the grow rooms or boxes is the number one reason for reduced yields or even complete project failure. It doesn’t take much effort to get it right, let’s have a look at some basic rules that will ensure your success.

There are 2 things to be taken into consideration before setting up a grow box - ventilation and circulation. Ventilation brings outside air into the room and removes stale air. Whilst circulation moves the air inside of the room. Both are essential as they contribute to the growth in the following ways:

  1. Deliver CO2 to plants which is what they basically breathe. Without proper ventilation in the room amount of CO2 reduces and plants start to suffocate. An exhaust fan pulls hot and humid air out of the grow room, creating a vacuum that pulls in cooler, drier air

  1. Regulate heat and humidity. Grow lights radiate a lot of heat which consequently also increases the humidity inside.

  1. Protect from pests and diseases. Warm and humid air is the best environment for fungi, mold, and several pests. Cooler and drier air reduces the risks of your plant getting attacked by a mile.

  1. Strengthen the stems. Plants feel the impact of the breeze and as a result, their stems grow thicker. That provides decent support for buds during the flowering stage and increases the yield.

The intensity of ventilation you need to provide solely depends on the number of plants you are planning to grow. If we speak just about 1-3 auto-flowering plants that will provide you and your best friends with decent stuff for a season, no special effort is required. Just keep a couple of windows opened in the house and make sure that your grow box is located somewhere on the way of the airflow.


When it comes to growing in bigger volumes and especially classic non-auto-flowering seeds, that may grow up to 2 meters tall. Some equipment will be required. As a higher number of bigger plants need much more light which respectively produces extra heat. In that case, installing two fans to ventilate the room will be a must. 

The rules of organizing the ventilation and circulation work the same way regardless of the space size. Whether it is just a grow box or an entire room, one fan should be placed for intake on one side and the other one of similar size should be installed for exhaust on the opposite side.


Check the cubic feet per minute (CFM) rating of the fan(s) and buy a fan with a CFM rating that’s higher than the volume of the room in cubic feet. The general idea is that you want sufficient ventilation to completely replace the air in the grow room once every minute. Simply measure the room’s length, width, and height in feet and multiply the three numbers. For example, if the room is 3-by-3-by-6 feet, 3 × 3 × 6 = 54 cubic feet, so a fan with a rating of 100 CFM would be sufficient.


The flow of fresh and dry air should cover as much of the grow box/room area as possible. Therefore the most optimal way is to install the fans in the opposite corners of the room. Your intake hole should be near the bottom at one end of the room with the exhaust hole at the top of the opposite end of the room. The exhaust hole is higher because heat naturally rises to the top. 


Even if all requirements are met, the final understanding of whether the circulation is sufficient is a way of trial and error. You may always need to add more fans, especially if Cannabis got really robust upon the completion of its vegetative stage. The goal is to have all parts of all plants “dancing” — all the leaves should be shaking gently. If you notice any part of any plant that’s not dancing, you may need to reposition the fan(s) or add a fan. A great way to start is to install 2 small fans in opposite corners of the room or one slightly larger oscillating fan in one corner of the room and make adjustments from there.

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