How To Ventilate Your Grow Room Properly

Why ventilation is so important for cannabis?

Like all plants, cannabis needs good air conditions to thrive for various reasons:

  • Keeping an ideal temperature, CO2 and humidity level
  • Avoid mold and pest issues
  • Stronger stems 

When growing indoors, you have the ability to fully control the environmental conditions of your setup with the help of ventilation equipment. This is crucial if you want to achieve the best results. Keep in mind that the objective is to offer the plant a "better-than-nature" environment where the conditions are stable and optimal for photosynthesis.

Although these variables change depending on the stage of your plant, the genetic and other variables such as the levels of CO2 here is a general rule of thumb:


  • 20-30°C
  • 70% humidity

Vegetative stage:

  • 20-30°C
  • 40-60% humidity

Flowering stage:

  • 18-26°C
  • 40-50% humidity

How can you ventilate properly?


Air exchange: 

The worst thing you can do is to keep your plant in a hot, humid environment where the air is stagnant. So the first thing you will need is good air exchange.

Depending on the size of your grow room or tent you will need an adequate and powerful enough fan to push the hot and humid air located inside of your growing space outside of the growing space (you don't necessarily need to exhaust it outside of your home). By doing this, negative pressure will accumulate inside of the room/tent and fresh air will be sucked in from outside.

Choosing the right extraction fan will depend on:

  • The type of light you are using and the heat they produce. HID setups tend to produce a lot of heat and in most case, you will have to think of using an air-cooled reflector which adds to the complexity of your ventilation system. Learn more about grow lights here
  • The size of your growing environment. For this, you will need to calculate the volume of air per minute that needs to be extracted which is calculated in CFM (Cubic-Feet/Minute). A general rule of thumb for this is to calculate the volume of your room/tent and multiply it by 3. For example, if you are growing in a 4'x4'x7' tent, the volume would be 112 Cubic Feet, multiply this by 3 and you get 336. So a good fan for this setup would be something equal or more powerful than 336CFM.

Here are some good in-line fans.





A very nice piece of equipment you can use for this is the Grozone TV2 which will automatically adjust the speed of your fan to keep the desired temperature. If you prefer to adjust the fan speed manually there are some dimmers available.



Air circulation: 

In order to recreate optimal outdoor conditions, you will need to move the air around in your tent just like a gentle breeze would do to make the plants sway. This will allow your stems to grow stronger and bigger which is essential to support the weight of the buds later in the flowering stage.

Moving the air inside your grow room is also a way to distribute the heat and humidity evenly creating steady conditions for each plant and will greatly reduce the risk of mold, bud rot mildew and pests like fungus gnats and spider mites.

Having a good air circulation system is very simple you will only need small fans inside your space. You can use regular pedestal fans but we recommend using a couple of clip fans or oscillating fans for better results.

Air Filtration:  

Filtrating the air in your grow space is highly recommended for many reasons. Not only will it get rid of the smell that can bother friends, family, and neighbors but it will also ensure the bacteria and other particles such as spores are kept away from your plants.

You will most likely need a carbon filter for this to complete your ventilation setup.

Learn more about air filtration and odor control here


Assembling your ventilation

There are various ways you can assemble the pieces listed above. It will most likely depend on your light and if you need to use a ventilated reflector or not.

For people growing with LED, the ventilation setup is pretty standard. There are again some variations but the principle is the same. You want the air going through the carbon filter before it passes through the fan and gets exhausted outside through the holes of your tent if you have one.

Most tents will have the required straps to hang the carbon filter and the fan on a top corner, this is ideal because this is where most of the heat will accumulate.


To connect this you will need some ducting, duct tape and clamps (optional)

Simply connect your fan and carbon filter together, secure them with duct tape then connect the ducting on the other extremity and secure with clamp and duct tape. Pass the ducting through the vent holes in the tent and make sure it's as air-tight as possible.

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