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Grow Tent Ventilation: What Home Growers Should Know



Though indoor growers enjoy a growing season that is often endless, grow room ventilation is often put on the back burner. Proper ventilation is key in running a clean, and efficient cannabis grow room, however. Without proper ventilation, weed plants tend to suffer from disease, stunted growth, and pest infestations. 

Not only is proper ventilation important in preventing disease and pests, cannabis plants thrive under an airy breeze that mimics the fresh air of the wild. Factors such as transpiration, and intense grow lights make the grow room hot, and humid, and without proper ventilation systems, these conditions are a ticking time bomb for the whole crop. Getting rid of the hot, humid air, and pulling in fresh cool air, increases both the speed of growth, and yields of marijuana plants. Good ventilation definitely pays its own way!

Join us as we outline good grow tent ventilation, and show you how you can install a simple system of your own.

The Basics of Grow Tent Ventilation

Why do you need to ventilate your grow room? It turns out there are a number of reasons. 

As we have mentioned, cannabis plants that grow outdoors enjoy the benefit of light breezes, evaporation, sunshine, and precipitation. Indoors, fans are substituted for breezes; watering systems take the place of precipitation, and grow lights make up for sunshine. 

A factor that is often forgotten is the free circulation of air outdoors, which is of great benefit to the plants. This is where cannabis grow room ventilation comes in. We will discuss exactly what an effective grow tent ventilation kit will achieve. 

A good ventilation system will:

Remove Excess Heat: Both grow room lights, and some plant processes emit heat. This heat could cause stress to the cannabis plant, and thus need to be ventilated out. 

Control Humidity: Humidity builds up quickly in cannabis grow tent ventilation setups due to the process of transpiration, and other processes. Failure to control this humidity could lead to mold, pests, and diseases. A good grow tent ventilation system will suck away some of this humidity and allow the plants to go on with their processes comfortably.  

Prevent diseases and Pests: When air remains stagnant, it becomes a prime candidate for the breeding of diseases, and pests. Powdery mildew, fungus gnats, mold, and spider mites have a preference for humid, stagnant conditions. Pests also lay their eggs in damp top soil. Having a fan dry out the top soil interferes with their reproductive cycle, while the breeze prevents them from establishing themselves on leaves, and stems.

Control CO2: Not providing fresh air from outside means that once your plant depletes its reserves of CO2 for photosynthesis, it has to slow down its processes. Ventilation brings in fresh air from outside that has new CO2, which ultimately boosts both growth, and yields. 

Introduce Wind Stress: Outdoor plants constantly get buffeted by the wind. This strengthens the stems, and makes them better able to sustain the weight of the buds later. Stems of cannabis plants that have not grown strong are sometimes unable to hold their own when the flowers start maturing. 


Why is Ventilation Important when Growing Cannabis?

As we have discussed, good marijuana ventilation has great benefits including:

  • Faster Growth, and Bigger Yields – In the right environment, cannabis plants grow faster, and yield more produce. Plants given the right environment grow faster and produce more bud
  • Temperature & Humidity – An effective exhaust system control both humidity and temperature, creating an ideal environment for the cannabis plants. 
  • Prevent Pests, and Mold – As we have seen, most mold and pests thrive in stagnant air that is humid and hot. Properly ventilating your grow room, and allowing fresh cool air to come in, reduces the chances of encountering these unwelcome guests. 
  • Stronger Stems – The breeze created by the fans causes stress that strengthens the stems. 
  • Air circulation – The use of more than one fan ensures that the air circulates within the grow area, and does not have damp spots. 
  • Cheap and stealthy exhaust options – When looking through grow room ventilation ideas, most are usually quite costly. That said, cheap, and stealthy systems do exist. 

Understanding Airflow in a Grow Tent 

Airflow (the way in which air “moves around” in your grow area) forms an important aspect of an ideal grow tent environment for growing your cannabis. Left to its own devices, the air in the grow tent will remain stagnant, and more often than not damp, hot, and depleted of CO2. That is why it is vitally important to ensure that proper air circulation is taking place. Indoor growers usually strive to create an environment that is even better than outdoors for their growing weed plants.

Proper air circulation involves getting rid of humid, hot air, and replacing it with cool, fresh air that has new reserves of CO2 required for continuing photosynthesis. The way air moves in your grow tent surprisingly has a big effect on the growth of your plants.

Plants grown outside have the benefit of enjoying the breeze, which is not only refreshing to them, but also strengthens their stems. 

To optimally create ideal airflow in a grow tent, the following factors have to be taken into consideration:

  1. An adequate exhaust system to “pump out” stagnant, humid, hot air.
  2. An inflow, which allows fresh air to get into the tents
  3. Oscillating fans which circulate the air in the grow room, and create a much needed breeze

Having these different elements allows for ideal grow room airflow, which in turn leads to the benefits we have discussed above including faster growth, stronger stems, and less pests and diseases.

What are the Best Exhaust Systems and how do you install them?

Evaluate CFM

CFM is the abbreviation for Cubic Feet per Minute, which is also airflow. It is the description of how much air a ceiling fan can move. Most exhaust fans in the US have a “CFM” rating. It is important to install a fan which has the correct CFM rating ideal for its size.

In addition to CFM, exhaust fans come in 3 sizes determined by diameter (the width of the fan). They are usually 4”, 6” or 8”. Most grow room ventilation setups will require the 6”, because most ducting and air-cooled hoods have a 6” opening. Adapters can be used where the sizes are not the same. 8” fans are usually used in more high-powered grows.

How to calculate CFM needed

  1. Determine your space's cubic area by multiplying” Length x Width x Height”. You want to move this amount of air roughly once every minute.
  2. Exhaust Efficiency – The exhaust taking out air will reduce the efficiency of your fan. Therefore multiply your previous number by two if the fan path is efficient (a short, straight line), or by 3 if the path is inefficient (a long way around turns). 
  3. Pick your fan. The fan you select should have a higher CFM indicated than the value you reached at above. When doing this, note that “booster” fans are not as strong as Inline exhaust fans.

Exhaust Fans

Now that we know how to calculate CFM, let us look at the grow room exhaust fans that will help us move hot and humid air out of our grow spaces. 

Designing an exhaust system that is efficient requires an understanding of how air flows in a room. The whole essence of a grow tent fan setup is to achieve a good exhaust system that creates negative airflow in your space, so that hot air gets replaced regularly by fresh, new, cool air. It should be your aim to replace all the air in your grow room every 1 minute, or if you live in a cool area, at least every 3 minutes. 

For you to be able to vent your grow room, at least one strong fan is required in your exhaust system. 

When in doubt, get a bigger exhaust fan that your requirements. You could always adjust its speeds downwards if need be, or switch it off altogether if it’s moving too much air. You could also control it by using a timer to regulate its speed. Due to the probability of needing to have more air moved in the future, it’s always more advisable to size up your exhaust fan. 

Window Fans

With window fans, you have to ensure that you have an intake hole, which could be another window, or a door, to let fresh air in. So, as the fan pushes hot, humid air out through the window, the inlet gets in fresh air. While installing your widow fans, ensure that they are all blowing out. This basically builds an exhaust system without having to use ducting. 

Though it is not as efficient as the ducting method, it can be used for small grows. As long as the outside is cooler than inside, it should work. 

Carbon Filters

Carbon filters absorb all the impurities from the air in your grow tent ventilation system, before releasing it into the environment. This also acts as a safety measure because the terpenes that let off a strong cannabis smell are also absorbed, concealing your activity. Carbon is very dense (one single gram boasts a surface area of 3,000 m2), and activated carbon filters are excellent for eliminating the strong smell of cannabis from your grow room.  

CO2 Injections

CO2 in supplemented quantities is known to speed up photosynthesis and the growth rate of marijuana plants. However, when designing an exhaust system with this in mind, it is important to note that the grow room needs to be sealed tight, and have extra lighting to ensure the added CO2 does not escape, and is used optimally. This should be done while still efficiently exhausting the hot and humid air.

As I’m sure you can tell by now, this is a much more expensive enterprise than the other ventilation systems we have discussed so far. However, if you want to reap the benefits of additional CO2, you might want to dig deeper into your pockets to provide sealed grow room ventilation that will be optimum for CO2 injection. 

Extractor Fans

Extractor fans are designed to pull the old air out of  your grow space. As hot air has the tendency to rise, your extractor fan should be installed at the top of your tent/room. Some reflectors or grow lights provide an attachment for fixing an exhaust system.  While considering an extractor fan, ensure to get one that is strong enough for your grow space (refer to the CFM calculations above). 

How to Create a Cheap Exhaust System

Creating a cheap exhaust system for your diy grow room ventilation simply involves doing away with duct, and not necessarily attaching the fan to your grow lights. As we have discussed in the previous section, you will need a grow tent exhaust fan and a window fan, and have an inlet to let fresh air in.

There you have it! A very cheap exhaust system.

What about smells? All the techniques that are normally used for the control of smells can work well with this system. Additionally, a carbon filter can be used to remove odor from the air on its way out. 

How to set up Grow tent Ventilation

  1. Set up your grow tent
  2. Install your exhaust fan right at the top of your room/tent ensuring it blows air out. Your intake hole should be larger than the exhaust, and located on the opposite side to your exhaust fan, and on the bottom of the tent. Though not always possible, it guarantees the best results. 
  3. Install a window fan which will blow hot air out of the grow room. You could also install your carbon filter at this stage, if you plan on using one. 
  4. Install your grow lights into your grow space with rope ratchets. However, do not plug anything in until just before you start growing.
  5. Apply ducting. Connect everything inside the grow tent with ducting.  You will need ducting clamps for this. Connect your carbon filter, to your light, and your light, to your exhaust fan. On the outside of the grow tent, install ducting that will exit the air from the fan outside. Use the ducting to connect your exit port with wherever you are exhausting your hot air to. Try to make the path straight, and short.

Final Tips on Grow Tent Ventilation 

While managing the airflow in your weed grow room might appear to be tricky, it doesn’t necessarily have to be. Following the tips we have outlined in this guide, and aiming to constantly replace your grow room air will provide the optimal conditions for your cannabis plants to flourish in

You are welcome to comment below, or share our article with other growers, and all the best of luck growing!


  1. Why is it important to ventilate your grow tent?

The hot and humid stagnant air found in grow tents can be prime for breeding mold, pests, and diseases. The depleted CO2 also affects the rate of photosynthesis are growth rate of the cannabis plants. 

2. How do you ventilate a grow tent?

Basically by using exhaust fans to push out the old, hot, and humid air, allowing fresh, clean air to come in.


Sebastian is a passionate advocate of CBD's therapeutic potential, dedicating himself to exploring its diverse benefits. As a seasoned writer, he eloquently shares his insights and personal experiences with CBD, aiming to educate readers about its transformative power. His life's mission is promoting holistic wellness, with CBD at the heart of his advocacy.