The Importance Of Air Circulation In Indoor Cannabis Grow

Why and how to stealthily exhaust air from your grow tent!
04 November 2020
7 min read
The Importance Of Air Circulation In Indoor Cannabis Grow

  • 1. Air circulation
  • 2. Why is air circulation important
  • 3. How to place oscillating fans in your indoor grow
  • 4. What is an exhaust system?
  • 4. a. How to choose the proper exhaust fan
  • 4. b. How to calculate cfm
  • 5. Use a carbon filter to eliminate the cannabis smell
  • 6. Diy stealth exhaust system step-by-step
  • 7. In conclusion

If you’re growing indoors you want a breeze all over your plants and an exhaust fan to pull the hot air and cannabis smell effectively, but it has to come out, and depending on where you live it can be quite dangerous to pull out cannabis-smelling air through your window.

An air exhaust is just as important as air circulation but doing it stealthily is more, you can easily do it using cheap and easy-to-find materials like duct tape and foam!

1. Air Circulation

Air circulation refers to the breeze that moves around your grow space, proper circulation can be achieved by having an oscillating fan. 


The importance of air circulation: air circulation

Proper air circulation in a grow tent.

This is needed to create a perfect growing environment for your plants and it’s important because air is present in nature, where cannabis grows naturally so if you want to grow great cannabis you will have to create good growing conditions and air is one of the ingredients.

2. Why Is Air Circulation Important

When you’re growing indoors, your plants are in an enclosed environment without access to natural wind, which is super important for cannabis plants in nature. When growing outdoors, there’s always a breeze flowing through cannabis plants that helps strengthen the stems and even protects them from pests.

Proper air circulation will bring several benefits such as:

Strengthens Stems

Air circulation helps strengthen stems by bending them a little bit, like wind would do in nature, over time, the stems will get stronger which is extremely needed when your plant is producing buds during flowering.


The importance of air circulation: benefits

Air circulation in big scale cannabis grow operations

An exhaust system ensures the air in your grow room is replaced regularly and that your plants get fresh CO2 and are in proper conditions and as you may know, good conditions results in the best growth rates.

Helps control temperature and humidity

The right combination of good air circulation and the proper exhaust system helps spread vapor and heat evenly throughout your growing space, this along with small fans blowing on your canopy and below helps homogenize the air, getting rid of humid or hot spots.

Reduces chances of getting mold and pests

When air blows over your cannabis plant, it carries away the moisture that is released during the transpiration process, this decreases the moisture level which also lowers the chance of your plants getting bud rot, powdery mildew, or mold in general.


The importance of air circulation: prevent mold

Airflow helps prevent mold like powdery mildew.

Also, the air that flows over your plants and soil makes it hard for bugs such as spider mites and fungus gnats to live in your garden, both of these bugs (and much more) prefer living in places where the wind isn’t strong so a proper air circulation will make bugs go away from your plants.

3. How To Place Oscillating Fans In Your Indoor Grow

Most indoor growers use clip-fans to create a nice breeze in the grow tent, this creates the proper air circulation that cannabis plants love and need to become stronger but have in mind that every fan is different and you’ll have to find the sweet spot.

When there’s too much breeze your plants will start to show signs of stress, these signs are known as “wind-burn” symptoms.


The importance of air circulation: place fans

Fans should be placed above the canopy and below so your plants get air all over them.

Wind-burnt leaves usually look droopy and can be hard to diagnose because they can look like they’ve been overwatered, overfed, or suffering from nutrient deficiencies

To be able to diagnose your plants properly when the leaves are droopy and curved (like claws), you should take a look at where the affected leaves are; If the affected leaves are in front of the fan and the others are not, is most likely your fans are too strong.


  • When placing your fans you want a nice breeze flowing around your plants, which means you want fans blowing above and under the plants;
  • Too much wind may damage your plants so don’t point them directly at your plants;
  • Check your grow tent thoroughly so all the plants get a slight breeze equally;
  • It’s better to have several smaller fans than one big fan, this will help you provide a gentle breeze without damaging your plants.

4. What Is An Exhaust System?

An exhaust system consists of a fan, ducting tube, and a carbon filter (optional), these equipments are needed to remove the heat emitted by your light fixture and other equipment in your grow tent.


The importance of air circulation: exhaust system

Good exhaust system installed in an indoor grow tent.

Without an exhaust system, the temperature in your grow tent will sit and may be too high for your cannabis plants, making it hard to control.

So to avoid mainly heat stress symptoms, an exhaust system is highly recommended.

How to choose the proper exhaust fan

Even if you live in a place where you don’t need to control humidity and temperature, you still need to exhaust old air and have new air in, providing more CO2 to your plants which is needed in the plants’ basic processes.

Installing an efficient exhaust system is quite simple but you need to understand how airflow works; The idea is to create negative airflow so that the air inside your grow tent is replaced with fresh air.


The importance of air circulation: exhaust fan

Exhaust system and roper exhaust fan.

All the air in your grow tent should be replaced every 1-3 minutes for the best results so ideally, you should replace the air every minute unless you live in a place where the conditions are not too harsh.

In order to do this properly, you should use a good exhaust system and calculate the strength you need based on the dimensions of your grow tent, which is usually measured in CFM.

How to calculate CFM

Cubic feet per minute (CFM) refers to how much air your fan can move per minute, it’s really important to get a fan with the correct CFM because this will affect the conditions inside your grow tent.

Exhaust fans usually come in 4, 6, and 8 inches but for home growers, 4in fans are recommended for smaller growing spaces and 8in for bigger grows so most home growers will be just fine with 6in fans.


The importance of air circulation: calculate cfm

How to calculate CFM.

First, determine the cubic area of your space, to do this you need to multiply the length x width x height, the resulting number should be the amount of air you need to exhaust once per minute. 

Second, have in mind that every exhaust system has some level of inefficiency because not every grow tent has the same setup.

In an efficient exhaust system, the air goes in a short and straight line after passing through the fan, and in an inefficient system, the air goes a long way after passing through the fan.


You need to have this in mind to make sure you’re moving enough air so:

Efficient system - multiply by 2

Inefficient system - multiply by 3

Remember that you need to pick a fan that has the same or slightly higher CFM number that you calculated. 

You will need a higher CFM if your grow space tends to get hot or humid, so it’s better to get a slightly bigger exhaust fan than a smaller one.

If you live in a place that doesn’t use the imperial system, here’s a table to help you know the exhaust CFM you need.


Grow tent size and CFM

Grow tent (foot)Grow tent (centimeters)Efficient system (CFM)Inefficient system (CFM)
2 x 2 x 4.560 x 60 x 1403654
2.5 x 2.5 x 5.380 x 80 x 16066.399.4
3.3 x 3.3 x 6.5100 x 100 x 200142212.4
4 x 4 x 6.5120 x 120 x 200208312
5 x 5 x 6.5150 x 150 x 200325487.5
8 x 4 x 6.5240 x 120 x 200416624
8 x 8 x 6.5240 x 240 x 2008321248


Remember that this is calculated in inches so if you are using the metric system, you should convert it to inches.

This table should help you choose the appropriate CFM based on the size of your growing tent and how you installed your exhaust ducting, remember that if you don't find an exhaust fan for your specific grow tent size it’s better to go for a bigger exhaust fan than you need, as long as you can adjust the speed you’ll be fine.

Also, you can buy a speed controller to control your fan or if you don’t want to spend more, turn the exhaust off for a couple of hours if it's affecting the growing conditions.

6. Use A Carbon Filter To Eliminate The Cannabis Smell

The best way to control the cannabis smell is with an exhaust system and a carbon filter, this is the most recommended method because it’s the only way to completely eliminate the smell.


The importance of air circulation: carbon filter

A carbon filter is the best way to eliminate smell.

A carbon filter isn’t hard to install at all but have in mind that the way you install, setup, and where you exhaust to is important so we’ll teach you a good way to exhaust stealthily.


7. DIY Stealth Exhaust System Step-By-Step

Even though you may already have a good exhaust system, depending on where you live, you’ll also need a good and stealthy way to exhaust the air.

Here’s a simple and cheap way to stealthy exhaust with materials that you can find at every construction store!

Materials needed

  • Duct tape
  • Ducting tube to match your fan’s size
  • Glue
  • Wicker blinds
  • Foam
  • Corrugated plastic sheet

Step 1

Install the wicker blinds on your window like you normally would, wicker blinds are ideal because air can go through but people won’t be able to see inside.


The importance of air circulation: stealth air exhaust

Wicker blinds allows you to exhaust without people being able to look inside.

Step 2

Glue the corrugated plastic onto the foam and cut it to be the exact size as your window, use your ducting tube to trace a hole near the top of the plastic and cut the hole, the ducting tube should reach the wicker blinds.

Step 3

Use duct tape to hold the foam/plastic in place and more tape to hold the ducting tube in place. The foam/plastic should be quite secure if you think it’s not then you should use a staple gun or another way to reinforce it.


The importance of air circulation: stealth air exhaust

The plastic/foam helps isolate the sound, making your exhaust system 100% noise-free.

Now that you’ve successfully made your stealthy exhaust you can continue growing without worrying, just remember that this is just one way to do it, you can do it any way you want, as long as it works for you it’s valid!

7. In conclusion

A good exhaust system and a carbon filter are extremely needed, doesn’t matter where you’re living. By eliminating the cannabis smell you prevent a lot of trouble that you may have if your neighbors or police end up knowing you are growing cannabis at home.

If you have other ways to exhaust air effectively and stealthily, please share it with fellow growers, leave a comment in the comment section below!


04 November 2020