Everything You Need to Know About Air Flow in Cannabis Cultivation

Setting up an indoor grow room for cannabis cultivation is all about the perfect lighting, well-balanced nutrients, and good genetics. Right? Wrong.

What many new growers overlook during the initial set up is the importance of airflow and ventilation (after all, beginning to grow cannabis indoors can feel challenging) Finding the best grow room circulation fans are a crucial piece to the puzzle of growing bountiful harvests. Airflow prevents mold, mildew, disease, and pests from taking hold. 

Do yourself a favor and plan grow room airflow and proper ventilation well in advance of planting a single seed or potting a clone. The best grow room circulation fans naturally mitigate many of the most common issues with indoor growing. It's the simplest solution, yet most often ignored.

If you are setting up an indoor operation for the first time or retrofitting an old one, don't neglect air circulation. Ventilation should be a top priority in your grow-room strategy.

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At its core, indoor growing is about bringing outdoor conditions inside - and then perfecting them. It's the fine-tuning of the seasonal light spectrum and schedule, providing the ideal hydration and balancing nutrients in the perfect soil, all in a way that mimics mother nature. 

Indoor air circulation is yet another way that the indoor grower must seek to replicate, and improve upon, the outdoor growing conditions.

Cannabis, when grown outdoors, is constantly exposed to weather conditions, including gentle breezes and gusts of wind. Natural conditions promote the growth of a strong plant and making it hard for disease and pests to take hold. Indoors, your goal is to create a similar exposure to constant air circulation.

The value of proper ventilation and constant airflow are as follows:

• Regulation of Humidity and Temperature

A key component to indoor growing is environmental control, meaning temperature and humidity control. If left unventilated and unmonitored, an indoor growing environment quickly becomes too moist and too hot. Proper airflow, combined with ventilation and environmental monitoring, creates an ideal ecosystem for your cannabis plants. 

Plus, with several of the best grow room circulation fans scattered throughout the grow, your indoor space will maintain a consistent temperature and humidity level from one side of the room to the other. This airflow eliminates some of the 'hot spots' which can develop in the inaccessible corners of the space. 

• Reduce the Risk of Mold and Mildew

What do you get when you combine heat and humidity? The perfect environment for mold and mildew. As soon as moist, stagnant air settles in under the canopy of your crop, you'll quickly find evidence of mold and mildew. In an indoor grow space, that can mean disaster if left unaddressed.

Boost the breeze through the canopy to mitigate issues with molds and powdery mildew. Again, a simple but highly effective solution.

• Increasingly Difficult for Pests to Take Hold

Take a peek under the canopy, are the leaves moving? Is there a constant stream of gentle airflow across the under foliage? Pests like spider mites and fungus gnats tend to move into areas with limited air circulation because their ideal environment is still and calm. They don't want to spend their tiny lives holding on for dear life in a strong headwind. They want to live and lay eggs where there is no breeze. 

Make your under foliage inhospitable to these pesky invaders, by creating better airflow.

• Creates Structural Integrity

Air circulation is also a critical aspect of the plant growth cycle. A room with a few of the best grow room circulation fans set up, creating a gentle wind through the canopy encourages strong, healthy plants.

Grow room fans mimic the conditions in an outdoor environment, and are critical to vigorous seedlings, and robust, mature plants. Strong plants produce better buds, as the stems allow for more efficient movement of water and nutrients.

All grow rooms are different, which means there is no one-size-fits-all blueprint for what your ventilation, fans, and circulation-system should look like. So, where should you start?

There are two critical components to a full indoor grow room ventilation system:

1. Room Ventilation (Intake and exhaust fans)
2. Air Circulation (strategically placed fans within the room)

Proper grow rooms, even cannabis grow-tents, should be outfitted with an intake/exhaust ventilation system. This system moves fresh air in and stale air out. If you plan on growing more than a single crop within your grow room, invest the time and money into a proper room ventilation system. 

The size of the intake and exhaust fan system depends on the size of the room. The industry rates fans by the capacity to move air in cubic feet per minute — or CFM. 

To calculate the CFM requirements of your space:

Width x Length x Height = Cubic Feet 

Cubic feet are equivalent to CFM, meaning a 100 cubic foot room, requires an exhaust fan with at least a 100 CFM rating. If you have an air filtration system, be sure to increase the exhaust capacity to account for this added strain.

On top of the movement of air into and out of your grow room, you'll also need to move the air consistently through the canopy. That means, strategically placing the best grow room circulation fans around and within the crop.

The placement of these smaller, often portable fans isn't as calculated. The goal of these smaller fans is to eliminate stagnant pockets of hot, humid air from settling in the corners of the room. 

The best way to determine fan placement is to monitor the room, especially once full of maturing plants. There should be fans placed above the canopy, and blowing within the foliage. Keep a very close eye on the nooks and crannies to ensure they don't need some adjustments to airflow as well.

Unless you've done this before (and maybe, even if you have), you likely have a few questions about proper airflow in cannabis cultivation. Here are a few of the most common questions:

Circulating fans (those blowing air around the room, but not into or out of it) can be left on 24 hours a day. Depending on the indoor grow you run, there is some debate about exhaust fans.

In highly controlled environments, the exhaust is often automatically connected to environmental controls such as temperature and humidity monitors. When the room registers above or below preset metrics, the fans kick in. Other growers recommend leaving the intake/exhaust fans on all the time.

To best understand grow room pressure, let's apply the concept to a grow tent. Negative pressure within the grow tent will pull the sides of the tent, while positive pressure will balloon the tent walls out. 

While the walls of a grow room won't suck in and balloon out like a grow tent, the concept is the same. Negative pressure pulls air in, while positive pushes it out. 

Positive pressure isn't ideal because it expels the aroma along with the air. Most growers suggest a slight negative pressure. If you need to adjust the pressure in your growing space, tinker with fan speed.

Such a common question, it's worth repeating. Calculating the CFM or cubic feet per minute required for any grow room is necessary to determine before buying an exhaust fan. Cubic feet is equivalent to CFM, therefore calculate cubic feet of your entire space:

Height (in feet) x Length (in feet) x Width (in feet) = CFM

Between the fans strategically placed in and around the cannabis canopy, and the intake/exhaust fans, the quality of the latter is by far the most important. Spending the time to find an appropriate model (with the features your room needs) can change the yield and health of your crop. 

There are a few features worth considering, including speed control, size, and responsiveness to temperature and humidity. You may also want to allow for the addition of a compatible filtration system.

Max Fan (both the Max-Fan Pro, and the Max-Fan Q-Max), focuses on performance and sound reduction. The Max-Fan Pro incorporates an acoustic muffler offering maximum sound absorption. If the hum of an always-on exhaust fan isn't exactly what you had in mind for your grow room, you'll want to look for brands like Max Fan, which cater to a quieter design needs. 

For growers who require a more intelligent and responsive design, the Cloudline is specially produced for a more controlled grow room. Their inline duct fan system works with automated temperature and humidity programming to control fan speed. Cloudline also connects to a branded filtration system, if desired.

As your design or renovate your indoor grow space, take care while planning the ventilation system. All plants, not just cannabis, needs the free movement of air to encourage growth, prevent disease, and to avoid infestation.

While it is impossible to recommend a single grow room circulation fan for your specific needs, the above details should provide a few helpful pointers. 

Plan for both intake/exhaust fans, and in-room circulation. Exhaust fans are sized based on CFM and come with several useful features, including soundproofing, filtration systems, and automatic controls. What you end up with is ultimately based on your strategic plan for the grow space. Just remember, a gently blowing canopy is a happy one.