Grow Tent Fans – Sizes, Placement, Setup, Accessories and FAQ
Having proper circulation in your grow tent is essential to preventing mold and powdery mildew from growing on your cannabis. I’m going to lay out everything you need to know about selecting a fan for your grow tent, and getting it set up properly.
I’ll help you determine the proper size fan for your grow tent, where to place the fan in your grow tent, how to set up your grow tent fan, and the other accessories you’ll need.
If that’s not enough, I’ll answer the most frequently asked questions from people across the internet who were in the same position as you.
An ideal temperature for cannabis plants is 70-80 degrees Fahrenheit. So if you’ve got a small grow light in a small tent, or other circumstances allowing you to maintain those temperatures without an inline fan, consider yourself lucky.
The downside to using a regular oscillating fan inside your tent is you’re pushing hot air around inside the tent. The hot air isn’t escaping and you aren’t pulling new cool air inside. It’s also not as easy to control humidity inside your grow tent unless you’re able to push out air when you have too much humidity.
Using an inline fan is also a great way to replace CO2 inside your tent. When your plants reach a decent size they’ll start to consume a considerable portion of the available CO2 in your grow space. One method to avoid that is by pumping out the old air and replacing it with new air.
Selecting the proper grow tent fan size:
The first question you’re probably asking is “What’s the proper grow tent fan size?” When you’re replacing air in a grow space, the general rule of thumb is being able to replace the air once per minute. Then you need to make a few additional considerations, such as 25% air resistance if you add a carbon filter, and 30% resistance for each 90 degree bend in your ducting.
The proper size fan for a 4x4 grow tent:
Let me give you an example calculation for a 4x4 grow tent, which is a pretty common size among indoor growers:
Most 4x4 tents measure 48in x 48 in x 80 in. So the total volume of air in a 4x4 grow tent is 4ft (length) x 4ft (width) x 6.667ft (height) = 106.67 cubic feet. But that doesn’t mean you need a 106 cfm fan.
When you consider a carbon filter reducing your fan efficiency by 25%, and one 90 degree duct bend reducing another 30%, a fan with 200cfm will get reduced to ~100cfm (200cfm x 0.7 x 0.75).
So for a 4x4 grow tent with an area of ~106 cubic feet, a grow tent fan (inline fan) rated for ~200cfm would get the job done.
What size fan is needed for other grow tent sizes?
I won’t write out all the math, but I’ll use the same method I used for the 4x4 grow tent above – one carbon filter and one 90 degree duct bend. I arrived at these estimations:
2x4x6.67 foot grow tent: 100cfm
3x3x6.67 foot grow tent: 125cfm
5x5x6.67 foot grow tent: 325cfm
8x4x6.67 foot grow tent: 400 cfm
10x5x6.67 foot grow tent: 640cfm
Note: grow tent fans aren’t always manufactured to the exact CFM output you need, so you may have to go over by 50-100cfm when picking a fan.
The AC Infinity fans mentioned below come with 10 speed settings, so if you only require 100cfm, you can buy the smallest model – a 205cfm fan, and run it on the middle setting for 100cfm.
Grow tent fan placement:
There are two options for placement of your grow tent fan. Either inside or outside the grow tent will work. What’s the difference? If you choose outside, the fan will pull air from the inside of your tent to the outside, via a duct on the top corner of your tent.
If you choose inside, you’ll want the fan and filter (if you use a filter) hanging in the top area of the tent where the hottest air naturally flows to. You’ll need these cheap hangers to hang your fan and filter from the inside ceiling of your grow tent. Not all fans include hangers, so make sure you’ve got them.
If you ask me I think hanging inside the tent is easiest. If you put the fan outside, you’ll need to find a way to make it rest in a good position.
The bottom of most grow tents has passive air intakes – netted windows allowing new air to flow into the tent. The new air gets pulled in naturally as the fan creates a low pressure environment inside the tent as air gets pumped out.
Grow tent fan setup:
The setup is fairly simple provided you have the necessary parts. Just make sure you have the proper size ducting (same diameter as your fan), duct clamps (usually included with ducting), hangers for hanging, and zip ties (make sure zip ties are long enough to go around the diameter of your carbon filter).
The carbon filter is optional, but it’s great for suppressing the smell if you’re growing cannabis, so I’d highly recommend it if you don’t want the cannabis smell traveling beyond your grow tent. To set up the filter, simply connect ducting to the side of your fan that sucks in air. Connect the other side of that duct to your filter. Secure both sides with a clamp (usually provided).
How to install a grow tent fan & carbon filter inside your tent:
- Attach & adjust hangers:
Attach the hangers along the support bars of your grow tent ceiling. You’ll need enough for the fan and ducting. Adjust them to the length you’ll be hanging the fan. Remember hot air stays at the top of the tent so don’t hang too low.
2. Attach zip ties:
Place zip ties or metal brackets on the attachment area of your grow tent fan. Connect zip ties to hangers.
3. Connect ducting:
Connect ducting to the output side of your grow tent fan, wrap zip ties or metal brackets around ducting and connect to hangers.
4. Connect carbon filter:
Connect your carbon filter to the intake side of your grow tent fan (the side that sucks air in). Use provided clamp or zip tie. You can connect it directly to the fan, or use ducting in between.
5. Run ducting through tent exhaust opening:
Run the ducting through the opening in the top of your grow tent. Secure the grow tent duct sleeve tightly around the fan ducting.
Which grow tent fans I recommend:
AC Infinity makes incredible grow tent fans as long as you’re willing to buy the ducts and hangers separately, which is straightforward – simply match the duct diameter to your fan diameter.
Why are the AC Infinity fans so much better than others? This fan comes with a programmable controller to allowing the fan to turn on when a variety of conditions are met.
For example, you can set the fan to turn on at a certain humidity level. You can also set the fan to turn on when temperatures reach a certain level. You can also utilize timer and alarm warnings.
The technology used in AC Infinity fan motors is such that the motors run very quiet. Other brands simply deprive the motors of power to adjust fan speed, causing the motors to get noisy. AC Infinity engineered a different method altogether that works much more efficiently and quietly.
These fans are priced similarly to other fans without the technical features, so it makes sense to go with one of these. The fans are made in 205cfm, 351cfm, and 750cfm (4-inch, 6-inch, 8-inch) variants. Click here to check them out on Amazon.
If you don’t want to source all the parts on your own, this kit comes with a fan, 8 feet of ducting, clamps, hangers, and a carbon filter. It comes in two different sizes for different grow tent sizes.
The only downside with this kit is the fan isn’t programmable to turn on when certain criteria like temperature or humidity are met. The fan is simple on/off. Although people have reported being satisfied having the fan run all the time. It’s up to you.
Secret Jardin made this 6-inch clip-on oscillating fan with grow tent owners in mind. The clip fits securely on grow tent support poles. The fan will provide your grow tent with proper air circulation needed to prevent mold and powdery mildew from growing.
I’d recommend pairing one of these oscillating clip fans with an inline fan to maintain the perfect growing environment in your grow tent.
What Else To Know When Setting Up a Home Grow:
In addition to picking the right size fan, I wrote several helpful lists and guides to help you complete your home grow the right way on the first try. Some other articles I highly suggest would be Picking the Right Size Grow Tent, This Year’s Best LED Grow Light List, and Understanding Grow Light PAR PPFD and Wattage.
Lastly, don’t forget to visit my home page for a complete list of helpful resources.
Grow Tent Fan & Carbon Filter FAQ:
How long will it take to hang my grow tent fan and duct?
30-45 minutes is all you’ll need.
What should I do if there isn’t a CFM output for my exact grow tent size?
The AC Infinity fans have multiple speed settings. So if you only require 100cfm, you can purchase the 205cfm (smallest model) and use the middle of the 10 speed options.
If I’m buying parts separately, how do I know if they’ll all fit together?
These parts are all measured by diameter. If you purchase a 6″ fan, make sure to purchase 6″ ducting and a 6″ filter. That’s all you need to know.
Do I need to hang the carbon filter?
Since the carbon filter is where air will be entering your fan, you should hang it near the top of your tent to capture the hottest air. Hanging the filter low or placing it on the floor would be inefficient.
Which end of the grow tent fan do I connect the carbon filter?
Connect the carbon filter to the “front” of the fan, meaning the fan is sucking air through the filter, not exhausting air through it.
What size fan will fit in my grow tent?
Most grow tents fit 8″ ducting, some may only fit 6″.
What if the size of my duct is too big for the duct hole on my grow tent?
If you have 8 inch ducting for a 6 inch grow tent outlet, you’ll need to buy a ducting reducer.
There’s too much negative pressure in my grow tent
Either lower the speed on your fan, open up the passive air intake windows on the bottom of your tent more if possible, or consider installing an active air intake fan, which is the same as your other fan but on the bottom of your grow tent pushing air inwards.
Can you wash or clean carbon filters after extended use?
You can clean a carbon filter with pressurized air. The filter is good for 1 year of use before it needs cleaning.
Can you place a carbon filter on each side of your fan?
Yes, but it may decrease your fan’s power efficiency a little bit. Make sure your fan is powerful enough to handle an extra carbon filter.
Do all carbon filters come with pre-filter wrap for the exterior of the canister?
Pre-filter wrap is not included with all carbon filters, make sure to check the product page details if you want a pre-filter included.
What’s the largest outer dimension of my carbon filter?
Add ~2 inches to the outlet size. The canister diameter on a 4 inch carbon filter would be more or less 6 inches.
How long do carbon filters last?
Carbon filters last at least one year of use.
Do I need inline and oscillating fans in my grow tent?
Inline and oscillating fans serve different purposes in the grow tent, so you should consider using both if possible.
1. Chandra, Suman, Hemant Lata, Ikhlas Khan, and Mahmoud Elsohly. “Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions.” Physiology and Molecular Biology of Plants 14.4 (2009): 299-306.
2. Backer Rachel, Schwinghamer Timothy, Rosenbaum Phillip, McCarty Vincent, Eichhorn Bilodeau Samuel, Lyu Dongmei, Ahmed Md Bulbul, Robinson George, Lefsrud Mark, Wilkins Olivia, Smith Donald L. (2019). “Plant Growth-Promoting Rhizobacteria for Cannabis Production: Yield, Cannabinoid Profile and Disease Resistance.” Frontiers in Plant Science 10. 10.3389/fpls.2019.00495