Proper grow tent ventilation is essential to healthy plant growth, and proper filtration is equally essential to clean the air and remove all odors. You should be replacing the air in your grow space at least every 5 minutes when the lights are on, and even quicker if your environment is struggling to combat heat.
On top of this, it is important to circulate your air within the tent. This will do a number of things to improve your grow, including keep temperatures and odors down, strengthen plants, and more.
We are going to share some useful tips for improving your ventilation and circulation within your grow room or tent. But first, let's start with the basics.
Passive or Active Air Flow
There are two ways you can set up the intake system for your grow tent: Passive vs. Active.
For the majority of grow tent growers, a passive intake system works perfectly.
Passive intake will actually not use an intake system. Instead, the inline exhaust fan will suck the air out of your tent creating a vacuum. This pulls in fresh air from the intake ports at the bottom of your tent.
As long as you have negative pressure inside the grow tent, you will have a passive system — negative pressure means your grow tent has less air pressure in it than the environment it’s sitting in.
With an active intake system, you will place an additional inline fan at the bottom of your tent to pull in fresh air through an intake port.
An active intake system usually isn’t needed unless you have a very large tent. You may also need one if you struggle with high temperatures, or your intake ports at the bottom are smaller than your exhaust ports.
Most tents have larger intake ports at the bottom so this isn’t much of a concern. If you plan on running a passive system and haven’t bought a tent yet, make sure to keep an eye out.
Sizing your ventilation system
To calculate the CFM you need to properly ventilate your grow space, use the following formula: (Grow Space Width X Length X Height) / 5 = Recommended CFM.
CFM performance of a fan is affected by the length and path of ducting. If you are using a carbon filter, this will further reduce your fan performance. Therefore, when using a carbon filter you must add an additional 20% to the CFM recommendation to account for the loss.
So, the formula when using a carbon filter would be: ((Grow Space Width X Length X Height) / 5) X 1.2 = Recommended CFM.
Once you have determined the necessary CFM for your space, you can decide on your ventilation setup.
If you are planning on using air conditioning or CO2 into the room to enhance plant growth, you will see the best results with the sealed room and utilizing a fan and carbon filter combo to scrub the air in a closed loop system.
Common grow room or tent ventilation setups
Your ventilation can be set up in a number of ways. Here are some possible configurations:
Again, keep in mind that the length and path of the ducting used can affect the total CFM performance of the ventilation system. It’s best to keep it as short and straight as possible.
5 steps to setting up your ventilation system
There are several ways you can connect the exhaust port to the inline fan to the carbon filter. How you set it up exactly will depend on how your lights are hanging and the type of grow lighting system you’re using — does it use a reflector or not?
When your ventilation components and tent are physically in front of you, setup and configuration makes sense, so don’t worry.
- Step 1. Attach your inline fan to one of the extra ceiling bars that your grow tent most likely came with — adjustable rope clip handles work great as you fan will hang only a few inches from the ceiling.
- Step 2. Either slide the inline fan over to fit into an exhaust hole or even easier connect your inline fan to the ducting which can be run through and out an exhaust hole.
- Step 3. Hang your carbon scrubber — it most likely will come with ropes for hanging.
- Step 4. Attach the carbon scrubber to the inline fan so that the fan is pulling air through the scrubber — you can use ducting or simply connect them if they are the same size.
- Step 5. Confirm your components are the in proper order: Outside air is passively pulled in through the bottom intake ports up into the filter (passing air through the lights), which then moves the air through the inline fan and out the exhaust holes.
Factoring in your reflector
For those using a reflector as would be needed for HID, your set up will be slightly more complex as it’s recommended to have direct airflow through the reflector, cooling the bulb.
If you want a more detailed guide on setting up your grow tent, check out our full grow tent setup guide!
Dealing With Heat and Humidity In Your Grow Room
If after setting up a traditional in-line fan and carbon filter setup you are still experiencing temperatures above your desired level (about 78 - 90ºF for seedlings and 72 - 76ºF for mature plants), you will need to turn to alternative methods of removing the heat.
Temperatures above 85ºF or below 55ºF will stunt plants, even if CO2 is being injected into the grow room. It is important to note that humidity control varies in open loop ventilation systems vs closed loop ones.
In open loop systems, one option is to directly ventilate the lighting through the use of an “air-cooled” reflector. These reflectors have ducting ports and can be hooked up to standard flexible ducting and ventilated by another in-line fan.
By removing the hot air being produced by the lights, you can see quite a bit of reduction in overall room temperature. Air conditioning is another option in extreme heat cases. We carry a number of different air conditioning styles with mini-split being the most popular.
Humidity control is also important in an indoor garden. Depending on the stage of plant growth, you will need various humidity ranges.
Controlling humidity in the room directly with a dehumidifier will greatly improve your environment. Dehumidifiers are available at Hydrobuilder, and act as stand-alone units that do not need ducting.
Dealing with Odor In Your Grow Room
A standard carbon filter will do the job in most cases. However, some growers may find that it isn’t enough for their particular strain or garden.
In these cases, first check your carbon filter. Make sure it is still usable, as the activated carbon loses effectiveness and the filter’s performance decreases.
Shaking a carbon filter can expose more of the carbon particles that have not been used in some cases.
All of these methods can be used together or separately as needed.
Grow Room CO2 and other Ventilation Tips
You will not want to allow the CO2 you add to your grow room to escape. Find a method of correctly dealing with heat and odor without venting the air outside of the grow room.
We want to keep this short, so read our full guide on using CO2 in the grow room here.
Be aware that ducting can transmit light into an otherwise light-proof grow room if not setup properly. If needed, creating a “u-bend” in the ducting can help prevent light leaks.
Also consider the use of a screen where your ventilation ducting makes it’s final output from your structure. This helps to prevent pests and animals from entering the system, and causing problems.
More information on setting up a ventilation system
This is a simple guide with some useful information, but we are just scratching the surface. The truth is, ventilation is incredibly important to the health and potency of your plants. There are so many things that factor into it, and so we encourage you to check out our definitive guide on grow room atmosphere and ventilation.
Here, you will learn more advanced ventilation strategies, along with how each factor in your environment affects the others.