Complete Ventilation Beginner’s Guide For Indoor Grow Room

August 30, 2021

An indoor growing system gives you absolute control over the growing conditions of your crops, allowing for year-round yields in any climate. But outdoor plant is constantly exposed to breezes and fresh air, a luxury unavailable to your indoor plant.
Proper ventilation can make or break a small grow space. Medicinal plants, like all plants, need fresh air and good air circulation to thrive. A properly ventilated grow room not only eliminates odors but also maintains a healthy growing environment. Installing an exhaust system to expel old, stale air and excess heat, in exchange for new cool air, can dramatically improve the health of your medicinal plants, yielding bigger, better harvests. In this guide, we’ll walk you through everything you need to know about properly ventilating your medicinal plants grow room/tent.

Different Extractor and Carbon Filter Configurations

Importance of grow room ventilation 

 1. Controls CO2

We all know plants take up CO2 (carbon dioxide) during photosynthesis.

If your system doesn’t have a ventilation system in place, CO2 levels your grow room will gradually decrease, limiting a crucial reactant for your plant’s growth.

Adequate ventilation draws in fresh CO2 dioxide from outside the growing environment and removes stale air, boosting the yield and growth of your plant.

carbon dioxide photosynthesis
Higher CO2 concentrations mean greater plant growth. Without adequate ventilation, you’ll suffocate your crops. (Flickr)

2. Controls humidity

Plants emit material throughout the day due to transpiration, a process where the plant “sweats” water through its leaves. This increases the humidity of your grow room.

Wet and humid air can trick the plant into thinking it’s been watered, halting both transpiration and the uptake of water and nutrients from its roots. If not corrected, this can cause several problems for your plant and sometimes even kill it.

An efficient ventilation system wicks away some of the water released in the transpiration process. The plant then absorbs more water and nutrients from its roots, resulting in better growth.

3. Prevents disease and pests

Pests and microorganisms love stagnant, humid environments. Fungus gnats, spider mites, powdery mildew, mold — you name it, they love humid growing conditions.

Damp topsoil is a favored nesting spot for pests. Proper air circulation can reduce the overall humidity in your growing area and dry the surface soil, disrupting any reproduction attempt by pests.

4. Removes heat

See those grow lights in your grow area? They emit heat. A lot of it.

Yes, even those lower-heat LED lights.

It may not look like much, but a few degrees of increase can mean the difference between a good yield and an unsuccessful yield.

Some types of grow lights (think, MH and HPS lights) emit more heat, but regardless of the type of light used, you can’t ignore the heat they produce.

5. Controls odor

Combining a carbon filter with a ventilation system can help eliminate unwanted odors. The two are crucial if you are looking to keep things discreet and under wraps.


Factors that dictate how to set up a grow tent kit ventilation system:

  • The size of your grow tent: is your tent small and you need to put the fan outside of the tent, but carbon filter inside?
  • The height of your grow tent: do you have enough vertical height to have both the fan + carbon filter inside the tent? Above the light as well or to the side of it?
  • Fan inside or outside of the tent: some people like keeping the fan inside the grow tent so that it can muffle the noise of the fan slightly.
  • Air-cooled lights or non air-cooled lights: air cooled lights will need ducting hooked up to them. This will mean ducing, fan, light, and the carbon filter all have to be in sync to connect to one another.

Choosing the Right Size Inline Exhaust Fan for a Grow Space

You'll want to consider the following additional specs before choosing an inline exhaust fan:

  • CFM
  • Duct size
  • Noise
  • Speed Controller
  • Carbon Filter Rating (if using)

Once you've worked out the estimated CFM, including all influencing factors, from the ventilation system to the outside climate, round up and look for options that fit this number. Inline fans are first based around CFM rating, and it should be easy to clean those rated above and below your grow tent target.

The CFM plays into duct size. The higher the CFM, the larger the duct required. Each inline exhaust fan uses a specific duct size (from 4" to 10" and beyond). Use the following as a general guideline:

4ft x 4ft = 4” Duct Size

5ft x 5ft (or 4ft x 8ft) = 6” Duct Size

Larger than 4ft x 8ft = 8” or larger
While noise won't play into your exhaust system's efficiency or functionality, it may be important depending on where you place the grow tent in your home or garage. Indoor growing is a lot noisier than some people expect, largely thanks to the need for a full ventilation system. If noise considerations are important, look for fans with silencer components.

For a bit more grow room control and flexibility, invest in a fan with a controller. This feature creates intelligent control over temperature and humidity programming, fan speed control etc.

It's always better to invest in a slightly larger fan, with speed controller, than you need for the system. This gives your grow room to expand, and gives you a little leeway in terms of CFM, without needing to buy an entirely new fan system.

Finally, if you are using a carbon filter, you'll want to ensure your fan is compatible. A powerful exhaust fan may push air through the filter too fast, making the filter ineffective. Always choose an inline exhaust fan with a lower CFM rating than the filter.

How to Calculate CFM For Your Grow Tent

 The workings here are quite straightforward. Using 10ft by 8ft by 8.5ft tent as an example, we can get the required fan size by performing the following calculations:

Note that there’s no converting the units into meters as we’ve already got the feet measurements as the base dimensions.

The volume of the active growing area = 10ft by 8ft by 8.5ft by 1.33 = 904.4 CFM.


While managing airflow in your indoor grow room might seem tricky, it doesn’t have to be. As long as you follow the tips in this guide, choosing the right ventilation kit, constantly replacing the air inside your tent or room, your plants will have the perfect conditions to flourish in.

You work out the correct calculations whether you’re working with European or American measurements.
Look at the fan's specs before buying, and, ensure that the CFM is enough for your grow room or grow tent.

If you want to know more about grow details, do not hesitate to contact us, the ECO Farm technician is always here to help you.

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