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Proper ventilation in your grow room is important. Just like humans, plants need air to survive. Cannabis plants need a certain amount of oxygen and carbon dioxide to grow healthy, as well as light and water.

Setting up a ventilation system will help you provide your plants with enough oxygen and carbon dioxide. It will also help control the temperature and humidity in your grow room which is important as this helps prevent mould, fungi and pests.

   

What is Grow Room Ventilation?

In nature cannabis plants are provided with fresh air and a nice breeze. When growing indoors you need to provide this air circulation for your plants. This is done through a grow room ventilation system. A grow room ventilation system ensures a continuous flow of air between the outside and the indoor grow area. It also includes some component for keeping airflow inside the grow room.

The most common type of ventilation system uses a combination of exhaust fans, ducting or pipes to maintain airflow and circulation fans to keep the air flowing inside the room. Larger tents may also include an intake fan to pull in fresh air.

  

Why is Air Circulation Important?

Maintain Co2 levels

A grow room is all about creating the optimal outdoor conditions indoors. This means you also need to maintain the perfect CO2 levels for your plants. In a closed system, the plants will soon run out of carbon dioxide as they use it for photosynthesis. They need an uninterrupted supply of fresh air from the outside. 

This will help boost the growth and yield from your plants.

Heat management

Plants are affected by temperature variations. A few degrees of change can affect the quality of your harvest.

Outdoors, the primary source of heat is the sun and the wind provide a cooling effect. In and indoor grow room, a grow light is used to replicate the sunlight. Some grow lights emit more heat than others. Having a constantly circulating air system will remove a lot of heat produced from the grow lights.   

Humidity management

Humidity attracts a lot of insects and other unwanted pests. It can also be damaging to the health of the plants themselves.

Along with the excess heat, a ventilation system can also remove the excess moisture in the air. Dry air also removes some of the water from the upper parts of the plant. This forces the plant to absorb more water through the roots and along with the water the plant also takes in more nutrition.

Mould and pest control

Still, stagnant and humid air has a negative impact on all surfaces of your grow room. The topsoil, or soilless medium, is particularly vulnerable. 

When air is stagnant, the medium will be unable to dry and will remain damp and humid. This creates an attractive environment and breeding ground for fungi, mould, mildew and many types of insects.

Air flowing over the plants and soil fight against unwanted pests like spider mites and fungus gnats by drying out the top layer of soil or medium. A constant air flow will also make it difficult for them to fly around. 

Strengthens plant stems

Having good ventilation in your grow room will help strengthen your plants stems. The gentle breeze strengthens stems by allowing them to bend and sway like they do in nature. This builds up the strength of stems over time, which comes in very handy when plants start growing bigger and get heavy from the developing buds.

 

Here is a quick list of all the benefits of having good ventilation in your grow room:

• Fresh air rich in CO2 and O2
• Removes stale air
• Gets rid of extra heat
• Stops air pockets from forming
• Stronger, healthier plants
• Better developed plants
• Helps control heat and humidity
• Less likely to get mould and pests

 

Different Ways to Ventilate Your Grow Room

Extractor fan

Extractor fans, also called exhaust fans, are installed to remove hot and humid air from inside the grow space. They are used together with ducting to direct the air away from the tent or room. There are 3 main types of extraction fans: Axial, Centrifugal and Mixed flow.

 

What is the difference?

Having good ventilation in your grow room will help strengthen your plants stems. The gentle breeze strengthens stems by allowing them to bend and sway like they do in nature. This builds up the strength of stems over time, which comes in very handy when plants start growing bigger and get heavy from the developing buds.

 

Here is a quick list of all the benefits of having good ventilation in your grow room:

• Fresh air rich in CO2 and O2
• Removes stale air
• Gets rid of extra heat
• Stops air pockets from forming
• Stronger, healthier plants
• Better developed plants
• Helps control heat and humidity
• Less likely to get mould and pests

 

Different Ways to Ventilate Your Grow Room 

Extractor fan

Extractor fans, also called exhaust fans, are installed to remove hot and humid air from inside the grow space. They are used together with ducting to direct the air away from the tent or room. There are 3 main types of extraction fans: Axial, Centrifugal and Mixed flow.

 

What is the difference?

Axial	Centrifugal	Mixed Flow	TD Silent Series Fan
Less pressure	Lower flow rate	High pressure	Mixed Flow
Higher flow rate	Higher pressure	Good Air Flow Rate	Very low noise level (27dB)
Comes in 4 (100mm),6 (150mm) & 8” (200mm)	Durable ceramic-coated metal housing	Very little noise
Noise rating: 46dB	Thermally protected AC motor	Combines the best properties of the Axial and Centrifugal fans
	High quality moulded impeller

 

Which One to Use - Axial, Mixed Flow or Centrifugal?

Mixed Flow would be the best option to go for in most systems, however Axial fans are perfect for smaller start-up systems. Centrifugal fans would be more ideal for bigger systems as it has a higher pressure which helps if you have a lot of resistance (Air-Cooled Reflectors, Carbon Filter, Ducting) in your system.

Intake Fan

An intake fan is used to bring fresh air into the tent. In smaller grow tents an intake fan is optional but in larger grow area it’s a good idea to use a intake fan along with your exhaust fan.

Oscillating Fan

These can be your average pedestal fans if you have space in your room. Many growers also use clip on fans which can easily be attached to a pole in your grow tent and adjusted to the correct height. Even with a good exhaust system it is recommended for growers to still place small oscillating fans in the grow space to blow air above and below the plant canopy for better air circulation and to help prevent any hot spots or humid pockets of air.

 

Factors to Consider for a Grow Room Ventilation System

1. How to choose a fan for a basic ventilation system

For new growers, a simple in-line duct fan is a great option. To find the best fit for your grow room or tent, you can find the CFM rating for the area.

CFM stands for "cubic feet per minute". It is a common ratio used to show how much air the fan can move in a minute. 

To calculate the CFM, you need to properly ventilate your grow space, follow these steps:

 

Step 1: Determine the cubic area of your grow space by using this formula: 

Grow Space Width X Length X Height

 

Step 2: You will then multiply this by the number of times you want the air to turn over or be exchanged. The general guideline is that you want the air to be replaced inside your grow room in one minute or thereabouts.

 For example, if you have a Grow Tent that is 1.2m x 1.2m x 2m you would need a fan that has a rating of around 172.8 m3/hour (1.2 x 1.2 x 2 = 2.88 x 60 = 172.8). 

The CFM of your fan should be greater than this number.

Now you have a starting figure to work out how powerful your extraction fan needs to be, you will also need to consider the following factors which can affect your final requirements:

 

Cool Environment: + 20%

Warm Environment: -20%

Air Cooled Reflectors: – 30%

Carbon Filter Included: + 20%

Long Ducting: + 20%

 

Example: If you'll be using a carbon filter in your 1.2m x 1.2m x 2m Grow Tent, the final airflow requirement will be 207 m3/hour (173 m3/hour + 20% = 207.36)

 

2. What size intake fan?

If you’re using an intake fan to draw in fresh air to your grow room it should be around 20% less powerful than your extractor fan, this prevents your tent from blowing up like a balloon and helps to keep odour contained.

 

3. What about ducting?

There are different types of ducting available such as flexible aluminium, insulated and heavy-duty ducts. 

Try to keep the ducting as short as possible as this will help reduce the distance the exhaust air has to travel. You should also keep bends and wrinkles in the system to a minimum.

 

4. What about a carbon filter?

A carbon filter is optional. If you don't mind the smell of your cannabis filling the room, then a carbon filter is not necessary.

 

How to Set Up Your Ventilation System

There are two different ways to set up your ventilation system for your grow room or tent: Passive vs Active

Passive Intake

For a lot of growers, a passive intake works perfectly for them. These systems only have a fan to blow out hot air from the tent. There is no intake fan to bring in fresh air. Instead, the inline exhaust fan will suck the air out of your tent creating a vacuum. This then pulls in fresh air from the intake ports at the bottom of your tent. As long as there is negative air pressure inside the grow tent, you will have a passive system. 

Negative pressure means your tent has less pressure in it than the environment it is in.  If more air is leaving the grow room (out-take) than entering (intake), you have achieved negative pressure. You will be able to tell this by looking at the outside of your tent. The vertical sides should be slightly pulled in, in appearance. This is because you have created a vacuum inside.

Negative pressure is beneficial to your plants as it makes it easier to control and maintain temperature, humidity, CO2 levels, and other contaminants because the hot, humid air is extracted from the tent quickly and constantly at the same rate. This allows for a stable environment within your grow room and avoids any risk of mould or mildew forming on plants.

For this system to be effective, the intake hole needs to be larger than the exhaust hole or duct.  

Active Intake

An active intake set up includes an extra fan called an intake fan, you will place this additional inline fan at the bottom of the grow tent to pull in fresh air through an intake port. This system is usually not needed unless you have a very large tent. An intake fan may also be needed if you struggle with very high temperatures or if your intake ports at the bottom are smaller than your exhaust ports.

Installing your ventilation system step by step

There are many ways you can connect the exhaust port to the inline fan and to the carbon filter. How you set it up will also depend on the type of grow lights you are using (does it use a reflector?) and how they are hung up.

1. Attach your inline fan to one of the ceiling bars in your grow tent. Adjustable rope clip handles work great as your fan will hang only a few inches from the ceiling.
2. Either slide the inline fan over to fit into an exhaust hole or even easier connect your inline fan to the ducting using a ducting clamp, which can then be run through and out an exhaust hole.
3. Hang your carbon filter with strong hanging rope.
4. Using ducting, attach the carbon filter to the inline fan so that the fan is pulling air through the filter.
5. Confirm your components are the in proper order: Outside air is passively pulled in through the bottom intake ports up into the filter, which then moves the air through the inline fan and out the exhaust holes.

 

Placing Fans in the Grow Area

Most indoor cannabis growers use small fans to blow air around within the grow area. This creates a nice breezy environment that cannabis plants love. 

Placing fans:

• You want to create a nice breeze surrounding the main canopy, which means you want air blowing above and under the plants.
• Don't point a strong fan directly at a plant. Too much wind can start to cause damage to the leaves and stems.
• Once you have placed your fans, check around the grow area to make sure all your plants are getting a slights breeze. Adjust your fans if you feel any stagnant air or lack of a breeze.
• Small oscillating fans are a great choice for the grow space because they are inexpensive and can be used to provide a gentle air flow to a wide area without blowing on any one part for too long.

  

Some Final Notes on Grow room Ventilation

Air flow and good grow room ventilation is an underestimated part of growing cannabis indoors. Ventilation is incredibly important to the health of your plants. Whether you are growing in a small or large space, supplying your cannabis plants with a regular amount of fresh air will keep them happy and healthy and minimise problems like mould, fungi and pests.