How Often To Run Exhaust Fan In Grow Tent

A grow room’s primary goal is to provide plants with a better growing environment than they would have outside. This also entails supplying clean, CO2-rich air.

A ventilation system is required to keep the CO2 concentration inside the grow room at appropriate levels for the plants. Because CO2 levels in the atmosphere are low, a steady flow of fresh air with proper ventilation from outside is required.

Plants are accustomed to growing in the open air, exposed to a gentle breeze from the elements and the wind. When deprived of such conditions, they can suffer.

You may wonder, do I need a fan for my grow room? The answer is, exhaust fans need installing in almost every grow tent to improve the conditions for your plants. But, you can also find there is more to finding the ideal exhaust fan than brand and price, such as expelling enough hot and humid air.

Guide in Running Exhaust Fan In Grow Tent

Other factors affect ventilation from your extractor fan system, such as how often to use them and the power they offer to maintain the temperature inside. Because of this, bigger isn’t always better as a too larger fan or using your fan too much use the fan too much; you risk injuring or harming your plants. (Learn How To Increase Humidity In Grow Tent)

In our guide, you can learn about should I leave my fan on when lights are off,

Should Exhaust Fan Always Be On In Grow Tent?

The length of time required for optimum ventilation will vary depending on the size of the grow tent.

There is, however, no specific time to display the run time. The fundamental reason for this is that each stage of the crop necessitates individual attention.

Here, you can learn more about fans on or off during dark period and also at the various stages of plant growth.

Lights ON

Heat is produced by lights, which raises the indoor temperature. Therefore, fans should move air throughout this lighting period. As a general guideline, tailor the right size fan and speed to your specific requirements.

Lights OFF

When the lights are turned off, the heat production automatically decreases. But, wait 20 minutes before lowering the fan speed, and then run your fans for at least 15 minutes per hour.

Location will also determine this because some locations are hotter than others. If the temperature in your location is high, you may need to run the fan for extended periods.

Seedling Stage

Run your exhaust fans throughout the day to ensure your seedlings grow correctly. The fan’s job is to maintain temperature and humidity, prevent the tent from becoming too humid, and allow a light breeze from adequate air circulation over your seedlings.

Flowering Stage

The flowering stage is crucial to the success of the plant’s development. When the lights are turned on, the fans should turn on. Allow at least one fan to run during dark hours. Some flowers may emit an odor during the late flowering stage, thus keeping the fans running for the duration, so these odors are caught in your carbon filter.

Night Time

Colder nights may not require ventilation and could rely on passive intake. During summer, many indoor grower will schedule fans to turn ON/OFF periodically in their grow space.

You can set the exhaust system timer to go off at midnight, so your grow room’s tent ventilation will balance itself come morning without causing too much negative pressure. (Read Rust Spots On Leaves During Flowering)

Proper measurement unit for running an exhaust fan

How Often Should I Vent My Grow Tent?

The proper measurement unit for running an exhaust fan is CFM. This stands for cubic feet per minute. This tells us how much air should be exchanged in the grow tent in question.

CFM is dependent on two factors. It depends on two factors: first, the size of the grow tent, and second, the size of the exhaust. The impact of the exhaust fan’s size, on the other hand, is so minor that it is frequently overlooked.

You need to know the mathematical explanation to calculate your sealed grow room ventilation.

In almost the whole space of almost all grow tent sizes, your exhaust needs to replace the air inside every three minutes. Therefore, divide the grow space total volume by three to optimize your scrubber fans and exhaust time.

This is the best moment to determine how much an exhaust fan should run within a grow tent of a certain volume.

However, it would help if you used grow space fans on the exhaust side rather than the input with more CFM.

This is because inside your grow tent, many factors begin to play a role, and these factors affect the ventilation of your grow tent. (Learn How To Sterilize Soil)

An exhaust with slightly higher CFM helps maintain the perfect ventilation that your plants are literally dying for.


As we all know, the process of photosynthesis is the kitchen of plants. Carbon Dioxide is the stock in that kitchen. Only proper ventilation can produce new carbon dioxide.

Without appropriate ventilation, the amount of carbon dioxide within a grow tent will become stale, which will be harmful to the plants rather than beneficial.

It needs to be set up high in the tent. Hot air rises, but denser cold air sinks. We need to get the heat out of the grow tents. As a result, exhausts are permanently mounted at the top.

Number of Plants

Make sure the plants in the grow tent don’t get too crowded. Plants are harmed because of these behaviors because they cannot realize their full potential.

If you want your plants to flourish as healthily as possible, don’t overcrowd the grow tent as demand from the plants inside could overpower the air intake, especially if there is no breeze because of the carbon filter.

How Ventilation System Affects Plants

A grow room’s ventilation systems primary goal is to give plants a better environment than outdoors.

A ventilation system is essential for maintaining ideal CO2 levels inside the grow chamber. Because the CO2 content in the environment is low, continual outside airflow is required, although you need to consider outside, where the carbon filer comes into play.
Here’s why an indoor grow room ventilation system air intake is necessary.

Grow Tent Exhaust Fans and Carbon Filters

Exhaust Fans and Carbon Filters

You need to bring fresh air into your tent and circulate it to offer the best chance of plant growth and to remove stale air inside.

An exhaust fan or inline duct fan can help here and use one to vent the hot air from your grow light, depending on the type of light you have. Inline fans pull air through a carbon filter, thus masking 99 percent of the scent.

Your exhaust fan should come with silver exhaust tubing to conduct the hot air from your grow tent and pass it through the carbon filter to stop any smells and also potential pathogens or bacteria.

A 4′′ exhaust fan with a carbon filter is recommended for modest growth. These will fit 90cm x 90cm x 180cm tents. If you are this size or larger, a 6′′ inline fan may be better. The 6′′ fan has two speeds, fast and slow, and may expand if desired.

One thing to know at the same time as which fan can reduce humidity is that airflow reduces the further it travels. So, it doesn’t matter if they are intake fans or exhausts fans; you need a straight path and as short as possible ducting to the outside.

When an exhaust fan is running, they do three things.

They reduce temperature and reduce humidity. The third thing they do is introduce cool air into the grow room to bring fresh CO2. Plants need this to flourish.

Factors that can affect the success of your fans are here:


HID and even fluorescent grow lights generate heat, mainly when confined. Temperatures of 80°F or higher are harmful to plants, so if your grow tent is indoors, the temperature will be around 70°F. The temperature rises once the grow tent lighting is turned on in any grow tent.

The hot spot to take a temperature reading can reach 80 degrees in less than ten minutes, and even running an exhaust continually, the temps won’t fall below 70 degrees as your home air is that warm.

In reality, a grow room will never fall below 75 or 78 degrees since you have a hot light inside, producing radiant heat and convection heat.

If you have other fans running continuously during the light cycle, you won’t have to worry about the tent losing CO2 or the humidity rising too high. (Read Growing Strawberries Indoors Under Lights Guide)

Running Time for Exhaust Fan

To figure out how long an exhaust fan should run within a grow tent, we must first measure it. This is because ventilation requirements vary for each grow tent.

A grow tent’s analysis should be in cubic feet. After measuring the space, we divide it by three to achieve the optimal exhaust fan running duration within a grow tent to fill the grower tent with fresh air.


CFM is the exhaust fan unit. CFM = cubic feet per minute. This tells us how much air should be exchanged in the grow tent.

CFM is reliant on two. It depends on the size of the grow tent and the exhaust. The impact of exhaust fan size is so minor that it is often overlooked.

Mathematical Explanation

An exhaust should replenish all the air for every grow tent every three minutes. Although, you need to calculate this based on tent size. Divide the overall volume of your sealed grow tent by three to optimize the exhaust according to the ideal exhaust duration.

How Often To Run Exhaust Fan In Grow Tent

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