How to Improve Air Circulation in Your Grow Room

Grow room air circulation is a vital part of each gardener’s set up. Too little air movement can allow mold, mildew, and other fungi to grow. Resulting in poor growing conditions and compromised plants. These can make for quite the headache and clean up, but with a few simple adjustments your grow room can be easy and breezy.

Increasing Air Movement


Fans are a quick and effective way to move increase air flow. They can be mounted on walls, ceilings or placed simply on the floor and used in conjunction with other fans to create consistent air flow over a large space.

Fans can also be set up with osslilating heads to move air in different directions around the room. The fan size should fit the grow space. They can be as large as industrial fans or compact as tiny computer fans. It all depends on the size of your individual space.

[PRO TIP] Being exposed to air movement from seedlings, stems and branches become hardier and more dense. This makes for strong and sturdy plants that can transfer nutients more efficiently. Resulting in a more more abundant harvest and a tougher defense against pest and disease. But remember air should not blow directly at plants at all times.

This can result in wind burns and do more harm than good. You can spot signs of this when the plant curls its leaves and has a slight “slump” in the branches. This issue can be resolved by having oscillating fans. You can also place a fan, on low, on one side of the room, and another fan, on high, on the opposite side to allow for an even distribution of air.


Ventilation is another effective way to insure proper air circulation for your plants. It is often used interchangeably with “fans,” but they’re not always referring to the same thing.

Fans move air through the room.

Ventilation refers to taking old air out of the room and replacing it with new air from an outside source. Installing intake and exhaust vents can seem like a major daunting task, but it doesn’t have to be if you know where to start.

Know Your Space

First off, multiply the size of the grow room, Height x Length x Width, to find the volume of air that needs to be moved for healthy ventilation. This will be measured in CFM or Cubic feet per minute.

The size of the room will determine how powerful the intake and exhaust fans will need to be.

For example, if the grow space is 8ft x 8ft x 12ft = 768 CFM (cubic feet per minute).

This is the least amount of air that needs to be moved per minute.
If you have a carbon or HEPA filter in place in the exhaust vent, it will require the air flow to work harder (by 25% at least) to escape the filter.

To account for any filters, multiply the total CFM of your space by 1.25.

Using the example above, this would look like:1.25 x 768 = 960Total CFM Needed with Filter

This means that an intake/exhaust fan has to have a CFM rating of at least 960 for adequate air movement through the example room.

All fans are required to have a CFM rating on their label. Matching the fans CFM with the size of your space is an easy task and a great place to start when it comes to ventilation.

[PRO TIP] HEPA Filters are installed to prevent mold spores and other microbes from entering the grow room. They keep your grow room contaminate free.

Carbon filters are used for neutralizing strong odors. So attaching a carbon filter to your exhaust vent will keep any powerful odors from leaking out into the surrounding area.

Be sure to replace or clean your filters by the replacement date (indicated on the package) to keep your space clean, healthy, and efficient.

Active or Passive Ventilation

Active Ventilation is by using fans or blowers to forcefully move air in and out of the grow space. This can be done by the use of fans or air conditioning ducts.

Passive Ventilation allows for air to naturally enter the grow space through an open intake port and only requires a fan to move the air out of the room at the exhaust port.

The intake port should be larger than the exhaust port.

This will let new fresh air in more easily, and let the exhaust fan work more efficient, while not allowing any excess CO2 to be trapped in the room.

The exhaust port is most effective if it’s higher on the wall than the intake port. This makes it easier to remove hot air, because hot air naturally rises, and will only require a little push to be removed.


There are four factors that go into keeping an ideal grow room temperature.

  1. Inside the grow room when the UV lights are off
  2. Inside the grow room when the UV lights are on
  3. Outside temperatures during the day
  4. Outside temperatures at night

Since indoor crops can be grown year round, deciding how you maintain an ideal grow room temperature is base on your climate and location.

During summer months if the outside temperature is over 100°F, and the grow room needs to be maintained between 70-80°F, once UV lights turn on the grow room is going to overheat. This means that your plants are going to suffer.

This is the reason why some growers opt for a night time “lights-on” cycle and a daytime “dark” cycle in their grow rooms.

This makes temperature regulation more manageable, especially if your intake air is from an outdoor source.

Control or Timers

Using controllers or timers can take some of the hassle out of maintaining the grow room. These have been used by many grower to regulate power to the lights, fans, air conditioning and vent systems. They can be as simple as a traditional timer from your local hardware store or as detailed as a digital interface, you can control and adjust from your phone.

[PRO TIP] Another great way to improve air movement and fight mold growth is to cut back the leaves and branches near the main stalk of the plant. Known as defoliation or pruning. This will allow air to move freely through the plant and keep mold and mildew at bay.

Whatever your grow room setup, adequate airflow and ventilation can go a long way in maintaining a healthy and happy crop for years to come.

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