Will an Inline Fan Handle My Heat Issues?

By Kent Gruetzmacher
Published: July 27, 2021
Presented by AC Infinity Inc.
Key Takeaways

If you are in the design phase of your indoor garden and still unsure if an inline fan exhaust system can handle your heat and humidity issues, we put together this brief guide.

The process of piecing together an indoor garden can be both costly and time-consuming. When setting up a new growroom or tent, you will often find hidden expenses around every corner. As such, it’s a good idea to thoroughly research available technology — including the most cost-effective way to regulate heat and humidity.


When setting up an indoor cannabis grow, you must consider the cultivation environment every step of the way. Even more, you need to weigh equipment expenses versus the environmental demands of your particular setup. Due to cost difference and ease of use, most growers would prefer an inline fan to a mini-split AC for regulating heat and humidity. While inline fans can effectively regulate the environments of most indoor gardens, they lose their efficacy in certain extreme circumstances.

If you are in the design phase of your indoor garden and still unsure if an inline fan exhaust system can handle your heat and humidity issues, we put together this brief guide.


Heat & Humidity Levels for Indoor Cannabis Gardens

For cannabis plants to thrive in indoor environments, cultivators must respect certain thresholds for heat and humidity. This threshold is also the baseline for understanding whether or not an inline fan exhaust system will handle the demands of your garden.

There is no question heat is the biggest environmental challenge that needs to be addressed by indoor growers. Not only must you consider outdoor temperature fluctuations, but you must also address the excessive heat given off by equipment — such grow lights. When designing your growroom or tent setup, you should always be thinking about how you will keep temperatures between 75-80°F.

Besides heat, humidity is the next biggest environmental challenge for indoor gardeners. Humidity levels over 50 percent are directly correlated to increased pathogen growth in cannabis — including both powdery mildew and botrytis.


Cloudline S10 inline duct fan from AC InfinityCloudline S10 inline duct fan from AC Infinity.

How do Inline Fans Work?

Inline fan technology has long been used in the HVAC industry. Because the primary focus of inline fans is to quickly exchange stale air for fresh air, they are popularly used to ventilate such areas as kitchens, workspaces, bathrooms, art studios, and laundry rooms.


Inline fans are built in a long cylindrical shape that matches the different circumferences of industrial ducting. When installed within a piece of ducting, inline fans pull air out of a room and propel it through a vent to the outdoors. How efficiently an inline fan works has to do with more than size, but also how it is situated with ducting and vents in a particular setup. If you have too many bends in your growroom ducting, your inline fan will work much less effectively in regulating heat and humidity.

(Read also: Feelin’ Fresh with Fans in Your Growroom)

Companies like AC Infinity have designed premium inline fans specifically for indoor growing. Their fans, such as the Cloudline S10, feature digital controls, adjustable speeds, as well as temperature and humidity gauges. Following these sensors, you can get a real-time readout of how well your fan is handling the demands of your grow.

How do I Size an Inline Fan for My Indoor Garden?

To help growers size inline fans for their gardens, manufacturers use mathematical equations and rating scales. Inline fan companies use the term CFM (or cubic feet per minute) to describe how quickly fans exchange stale air for fresh air in a growroom. Importantly, CFM figures are used to define the specific size of your room or tent, as well as the air-moving capacity of particular inline fan models.

To match the environmental needs of your garden versus the air-moving capacity of different inline fans, you must first figure out the baseline CFM needs of your room. This simple equation will give you the CFM rating of your room: height x length x width.

As a baseline, a 5ft x 5ft x 6.5 ft grow tent requires a fan with a minimum CFM rating of 162.5. However, you must also account for other factors that will lessen your fan’s overall efficiency. Most notably, long pieces of ducting and excessive bends in your ductwork reduce the effectiveness of inline fans. The added heat produced by grow lights will also increase your minimum CFM needs. While it is difficult to employ a single equation to cover all the possible variances in an indoor garden setup, most manufacturers agree you should at least double your original CFM rating. Consequently, at a minimum, the garden in question requires an inline fan with a CFM rating of 320.

Fan inside a ventilation duct.

Seasonality & Weather Considerations

While mathematical equations and CFM ratings are an excellent way to gauge the efficacy of an inline fan exhaust system, these setups eventually meet a threshold when facing the rigors of hot climates. Importantly, changing outdoor temperatures directly influence how well your inline fan exhaust system will be able to regulate heat in your indoor garden.

(Read also: Four Things You Need to Control in the Growroom)

A majority of locations in North America enjoy the environmental diversity of the four seasons. As the calendar year progresses, most indoor cannabis growers can safely cultivate indoors with an inline fan exhaust system in the fall, winter, and spring. Depending on how efficiently you have setup your garden, you can safely assume it will run at least 15-25°F hotter than the conditions found outside. This temperature gradient will vary with factors such as grow lights (LEDs vs DE HPS), room insulation, as well as the ambient temperature of the building where you are growing.

Summary: Will an Inline Fan Work for My Indoor Cannabis Grow?

In most conditions, as long as you run your lights at night, you can generally rest assured that the right sized fan will keep your room cool enough. However, when outdoor temperatures average more than 60°F at night during the summer, most inline fan setups reach their threshold.

To keep overhead costs minimal, and lessen electrical expenses, many indoor farmers opt to only grow cannabis during the fall, winter, and spring. In doing so, you can avoid purchasing an extremely expensive mini-split AC unit that will only be needed a few months of the year. Even more, by shutting down your indoor grow in summer, you can avoid the exorbitant electricity expenses that come with operating on an overloaded electrical grid.

AC Infinity LogoAC Infinity is the foremost name in air delivery systems, designing and developing the latest innovations in cooling and ventilation technology. They offer a suite of quiet inline fans that automate the growing progress and track key metrics. Visit or contact [email protected] to learn more.


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Presented By

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Written by Kent Gruetzmacher | Writer, Owner of KCG Content

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Kent Gruetzmacher MFA is a Colorado-based writer and owner of the writing and marketing firm KCG Content. Kent has been working in the cannabis and hydroponics space for over a decade. Beginning in California in 2009, he has held positions in cultivation, operations, marketing, and business development. Looking specifically to writing, Kent has worked with many of the leading publications and marketing agencies in the cannabis space. His writing has been recognized by such icons as Steve D’Angelo and Rick Simpson.

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