Grow Tent Ventilation: Importance of Proper Airflow

ventilation system for cultivation

When someone finally decides to roll up their sleeves and start growing their own medical cannabis at home, the first step is to put the Internet upside down, digging for information.

“Where can I buy seeds?” “What’s the perfect soil to grow weed?” “Should I get sativas or indicas strains?” “What’s the ideal temperature for my grow room?”

And even if these are valid questions, they often forget about one essential piece related to the room climate: ventilation.

Getting proper airflow and ventilation in your grow room is as important as getting the right temperature and light hours.

Why Do You Need Good Ventilation in Your Grow Room?

Suffice it to say that airflow plays a key role in regulating temperature and relative humidity levels, two factors that can make the difference between a successful harvest and a maybe-next-time harvest.

Airflow also helps to cleanse your plants. When marijuana grows wildly, natural breezes take care of this. However, when growing indoors, you must wear the Almighty God hat and replicate breeze, rain, and sunlight for them.

Let me fully convince you by listing everything good ventilation will do for you.

Removes Excess Heat

Now, if you’re smart enough and have already invested in LED grow lights, you may proudly pat your own back and know you’ll barely have heat issues. However, you still need an extractor to exhaust stale air and draw in the fresh air.

On the other hand, HID light growers have to deal with hotter grow rooms. And even a slight temp change from 29°C to 32°C can have disastrous consequences for your crops.

Controls Humidity

Good ventilation takes down humidity levels inside your grow room. Having accurate relative humidity is a good thing; we don’t want our plants to dry out and die. However, uncontrolled humidity can foster poor growing conditions and disrupt your plants’ growth.

Ventilating your grow room correctly wicks away excess moisture from plants’ transpiration, leading them to draw in more water and nutrients from the soil.

Avoids Pests and Diseases

Pests and diseases are likely to thrive and take over in a highly stale and humid environment, so you could end up struggling with mold, powdery mildew, spider mites, or fungus gnat.

However, if you run a fan to ensure good airflow, the soil’s surface remains dry, and pests won’t be able to lay their eggs. Even if they do, the constant air movement helps to slow their reproductive cycle and makes it harder for them to establish.

Controls CO2

Plants and humans have the greatest deal ever. They need CO2, and we need O2. So, they absorb CO2 during the day and give us back O2. If your grow tent is sealed, the CO2 level will slowly decrease, disrupting your plants’ photosynthesis.

Every seasoned grower knows that adding extra CO2 to your grow tent has significantly positive effects on your crops. This is because while the levels of C02 in the air are, on average, 390 ppm (parts per million), marijuana can synthesize 1500-2000 ppm.

On the other hand, CO2 regulators are quite expensive, so you need to compare the benefits against the investment cost. The best way to keep the CO2 level from dropping is definitely drawing in fresh air.

Airflow vs Ventilation

Although it may sound like it’s the same for first-timers, airflow, and ventilation play different roles in the overall health of your grow room environment.

You can have oscillating fans mounted up on your walls to achieve a nice airflow. These won’t cool off your grow room, but they circulate the air within, helping to minimize hot spots. A fresh breeze batting your plants also replicates the natural wild outdoor wind, stimulating stronger stem growth.

On the other hand, ventilation refers to having an air extraction system to clear out stale and hot air while letting fresh air in. You could have a passive or active air intake system, but you need a system to exhaust stagnant air either way.

Passive Intake

Passive intake refers to using a fan to extract stale air but letting the air in naturally. If you’re opting for this type of ventilation, you will place a fan to blow stagnant air out, and you will have a hole in your grow room that allows fresh air to enter, thanks to the pressure differences between the inside and the outside of the grow space.

You should have more than one passive intake hole or ensure it’s at least three or four times the size of the exhaust hole. This will allow proper suction and ventilation without your fan overworking.

Also, be mindful not to let air in from outdoors if you go through cold winters.

Active Intake

Active intake systems have one fan blowing air out and another drawing air in. With these active ventilation systems, you don’t need a larger intake hole, so it may actually make things easier for you.

Tips for a Perfect Grow Room Ventilation

Invest in an Extractor Fan System

First things first. The best time to buy and set up an air extractor fan system is right when you’re setting up your grow room or tent. It will make things much easier for you as you won’t need to work and manipulate things around your fragile plants.

Second, this ventilation system needs to be large enough to renew the total volume of air in the room every few minutes, ideally, every two minutes. To choose the right fan, we need to know the room’s capacity and the fan’s exhaust efficiency.

How to Calculate Fan Efficiency and Room Capacity

Room Capacity

You just need to calculate your grow room’s volume.

Length x Width x Height = Volume m3

If your favorite grow tent is 1.2m by 1.2m by 2m, then the total air volume in the room is 2.88m3.


CFM stands for cubic feet per minute, which measures the total amount of air an extractor fan can move.

Following the previous example, if you need to renew the air every two minutes, that would be 30 times an hour. So, 2.88 X 30 equals 86.4m3/hour, which is 50.85 cubic feet by minute (CFM). You can easily convert from m3/h to CFM using this online calculator.

Use the fan CFM as a starting point and look for higher CFMs. Now, if you’re using HPS grow lights that put off a lot of heat and you also need to cool off your grow room, it’s a good idea to at least double that figure.

CO2 Injections

As we mentioned before, adding extra CO2 to your plants positively impacts their growth and development. However, before adding it to your grow tent, you need to consider a few things.


CO2 injections are an expensive investment to do. If you are on a tight budget and feel happy with your resulting yields, know that it’s perfectly fine not to use it.

On the other hand, if you can afford it and you feel like experimenting, do some research and go for it.

CO2 system


Increasing so much the CO2 levels may be beneficial for plants, but hazardous for humans. Make sure that extra CO2 pump does not leak into your house, putting you and your family in a potentially harmful situation.


For CO2 injections to be effective, you need a sealed grow room or tent. Actually, the very first reason to seal the grow tent is to prevent the CO2 from leaking out and intoxicating your house. The second is that CO2 injection efficiency is noticeable in very high concentrations.

Finally, for the plants to make the most of their CO2 injection, you will need bright lights to boost the photosynthesis rate and plant growth. Also, consider getting a thermostat, as you may face a 5°C increase in the grow room temperature.

Read Also: When to Stop CO2 Injections During Flowering

Humidity Levels

You can control your grow room humidity by controlling the ventilation. Humidity control is the perfect definition of a “middle point.” Too low humidity levels will cause your plants to dry out; too high humidity levels will welcome pests and diseases to prey on your precious marijuana plants.

So, depending on your needs and your local climate, you can either get a humidifier or a dehumidifier.

For example, lowering humidity levels is simply done by venting humid air out and letting fresh air in, as long as you don’t live in the Caribbean and the intake of “fresh air” is as humid as the air inside the room. In that case, you can get a dehumidifier.

On the other hand, to quickly raise the humidity, seal your grow tent and turn off your air extractor system. Or you can just get a humidifier. 

One Final Word

Hopefully, you are now ready to implement your ventilation system and grow gorgeous plants at home. As a final take, remember that choosing the right size ducts can also smooth the ventilation within your grow room. Focus on getting shorter ducts with fewer bends to optimize the airflow in and out.

Also, remember all these climate factors are closely related to one another, so don’t forget to monitor your grow room temperature.

Happy growing!

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