Fundamentals Of Cannabis Grow Box Ventilation

Fundamentals Of Cannabis Grow Box Ventilation

Ventilation is crucial for the cultivation of healthy plants – in fact, it is one of the most important factors. In other words, if you don’t have good ventilation in your grow box, your plants could end up dying.

Why Is Ventilation Important For Your Grow Box

Ventilation controls air quality, CO2 levels, heat, and humidity in the grow box. To ensure good air quality, you need to provide sufficient air circulation (air exchange). The required airflow will vary depending on the temperature outside the box. To achieve adequate airflow, I recommend getting good fans. Fans will help create the necessary conditions in the grow box. By circulating air, the fan will give you control over the following factors:


One of the fundamental functions of fans is to reduce temperature, which quickly accumulates in indoor cultivation due to limited space. The ideal temperature in the growing space should be between 70°F-83°F (21-28°C) when lights are on. At night, aim to keep the temperature from dropping by more than 9°F(5°C). Allowing the temperature to fall below or rise above these limits could seriously endanger your plant’s health.


When lights are on, aim for humidity levels between 40-75%. High temperature and excessive air circulation can affect relative humidity. High temperature reduces humidity, creating unfavorable conditions for the plant. This issue is more prevalent in summer, so using a humidifier may be necessary. If the humidity in the grow box drops very low (below 40%), it can cause young leaves to become smaller, while larger leaves may curl, dry out, and fall off. It’s important to note that such stress can slow down the growth or stunt the development of your plants, especially in younger ones. Larger, older plants naturally increase humidity in the grow box.

During the winter months, there’s a low probability that you’ll need a fan to regulate humidity; instead, you’ll likely use them more for temperature regulation. Air exchange is less frequent in winter, and plants naturally increase humidity. However, excessive humidity can create a perfect environment for the development of fungal diseases. Plants are particularly vulnerable when lights are turned off, temperatures drop, and humidity increases. In fact, inadequate ventilation is the main cause of most fungal diseases. Let fresh air flow, and you can forget about moldy tops.

plant in well ventilated grow box

Air Circulation

Installing an additional fan in the grow box during winter is one way to achieve equal distribution of CO2, humidity, and temperature regulation. This additional fan would be used to mix the air inside the box.


There are many different types of fans, and here we’ll explain circulation and exhaust fans. We’ll also touch on how to improve ventilation with additional equipment.

Circulation/Exhaust Fan

This fan is a critical part of the grow box ventilation. It is capable of removing heat and moisture from the box. However, to get the most out of the fan, you need to determine the necessary amount of air the fan must exhaust. 

You can find the necessary fan capacity in cubic feet per minute (CFM) by multiplying the volume of your growing space (in cubic feet) by the air exchange rate (in minutes). Use the formula (L x W x H)/3 = CFM to make this calculation. This will serve as an initial reference for choosing the suitable exhaust and intake fans for your ventilation setup.

However, often, though not necessarily, an intake fan is also needed. We recommend having both exhaust and intake fans. If you don’t have an intake fan, your exhaust fan could have 25% less exhaust power than its stated value. When cooler air enters the box, it’s important to ensure that the air mixes well with the warm air. Mixing the air will help minimize the negative effects of cold air on your plants.

fan used for grow box ventilation

Ways To Improve Your Grow Box Ventilation 

Modify the Grow Box

You can reduce the need for ventilation by modifying the box. For example, using a fan to cool bulbs can prevent the heat generated from the bulbs from entering the plant space. This also reduces the likelihood of “hotspots” by bringing the bulbs closer to the plants, allowing better utilization of CO2.

Fan Positioning

Place the intake fan at the bottom, diagonally opposite the exhaust. Remember, the exhaust fan should be as high as possible. This placement allows fresh air to circulate through the entire box, picking up warm, moist air as it goes. Use parts designed for each fan when installing to avoid vibrations.

Use a Thermostat

To achieve precise climate control in the box, whether it’s summer or winter, it’s worth investing in a thermostat. Proper air exchange is critical for successful cultivation. However, fans at higher speeds create a lot of noise, which can sometimes be a problem! Combined together, speed control and a thermostat will allow you to control the amount of air exchange per hour. It’s important to regulate airflow, and it’s not the same whether it’s summer or winter, so this can help reduce or increase the air exchange in the box. Fans will constantly run at a reduced speed, just slightly below full speed, if the thermostat is activated.

Noise Reduction

If noise is a significant issue, consider using “acoustic ducting” (sound-insulated pipes). These pipes reduce noise by almost a third. About 3ft (1m) on each side of the fan is needed to achieve the best effect. The use of silencers is also a good way to reduce noise. Silencers allow the use of powerful ventilation in small spaces, useful when you have many bulbs and need strong ventilation. For the best effect, attach silencers to both sides of the fan. This will reduce noise by 2/3.

Odor Control 

Certain cannabis strains produce a strong smell which can sometimes be an issue. A professional carbon filter connected to the exhaust will help with that “odor.” It can remove between 90-95% of the smell, allowing you to grow whatever strain you want. 

However, it’s important to connect the right filter to the right fan. Unpleasant odors have a “dwell time” that must pass before they are completely absorbed. So, a 26,000 ft3 (750m3) fan will need a 26,000 ft3 (750m3) filter. Don’t try to use a filter with a lower capacity; it won’t work as it should!

fan used for grow room ventilation

Final Word

Ensuring proper grow box ventilation is crucial for establishing and sustaining an ideal growth environment for your cannabis cultivation. By grasping the elements of a proficient ventilation system and incorporating budget-friendly do-it-yourself solutions, you can enhance yields and promote robust plant health while curbing odors and upholding a regulated climate.

Armed with the knowledge and tools necessary to forge an efficient ventilation system in your cultivation space, you are well-positioned to embark on a successful journey as a cannabis cultivator. Best of luck, and may your growing endeavors be both prosperous and fulfilling.

1 thought on “Fundamentals Of Cannabis Grow Box Ventilation”

  1. Pingback: Complete Guide to Growing Cannabis - Canna Capable

Comments are closed.

Scroll to Top