As an indoor grower, one thing that should never escape your mind is the ventilation of the grow room. Many indoor growers fail to recognize the importance of proper ventilation to their crops, and this leads to poor returns from their hard work..

Whether you are using grow tents, cabinet room, or any other form of grow-room, keeping a stable environment is the surest way of getting good returns.

Cannabis plants absorb all of the Co2 available around them within around one minute, which is why you’ll need to set up fans near your plants; they distribute any new air around the Indoor grow tent so that all of your plants have access to a constant stream of Co2 and so that your plants aren’t affected by stagnant air, which can cause illnesses and humidity.

With just a little extra airflow, your plants will be able to breathe much better, improving photosynthesis, nutrient absorption and generally increasing your plants’ strength; the branches will grow stronger thanks to the slight wind resistance, which means that during the flowering period they’ll be able to grow thicker, heftier flowers.

At the same time expelling the air inside will keep temperature and moisture build-up under control, preventing mold and mildew from forming on your plant’s leaves, inhibiting growth.

What Size Fan Do I Need For My Grow Tent?

Fan size is not what’s important. It is fan capacity.

First you need to figure out the capacity you need. And the capacity then determines the fan size. For most home growers this will end up being a 4 or a 6 inch fan.

How do we figure out the fan capacity you need for your grow tent Inline Duct Fan?

By following the calculation we’ll cover next. Or you could scroll down to our table and see if your tent size is on there.

Then you can just use the capacity provided in the table.

Quickly Create the Perfect Environment

When used correctly, a grow tent lets you recreate nature under its most ideal conditions! Possibly the hardest part of being able to grow cannabis in these ideal conditions is getting set up. However, once everything is set up, it’s mainly a matter of planting a seed and watering your plants until you harvest bud!

If you’re trying to create a growing environment from scratch, you may have to do some DIY which can feel overwhelming if you’re just getting a grasp on growing. Utilizing a grow tent takes care of a bunch of environmental factors in one fell swoop.

• Maximize Your Grow Lights – A grow tent has reflective walls and the reflectivity is equal or often even better than what you could do yourself!

• Designed for Common Grow Equipment – It’s easy to hang and adjust your grow lights, hook up your fan, find ports and vents, etc. A grow tent accounts for most growing situations.

• Light Proof – A grow tent is constructed to prevent light from leaking in or out of the tent. Not only does this help your plants (cannabis needs complete darkness at night to make as many buds as possible), it also prevents light from spilling out; you don’t want to possibly alert others that there are some very bright lights inside your home! Sometimes DIY light proofing a space can be tricky, and a grow tent takes that problem out of the equation.

• Waterproof & Easy to Clean – A grow tent usually has a waterproof floor that contains regular spills so you don’t have to worry about water leaking out onto your floor. It’s also easy to wipe down the walls and floor of a grow tent, making it simple to keep things clean.

• Designed for Airflow – The sealed nature of the tent combined with vents and air ports make it so you can set up a whirlwind of air in the tent simply by installing a strong exhaust fan in one of the included ports. This constantly pulls fresh air in to circulate through the tent from the intake vents near the floor, replacing all the air in just minutes while giving plants plenty of CO2 and preventing problems from heat buildup.

• Smell-Proof – Grow tents make it really easy to take advantage of a carbon filter. The negative air pressure caused by the sealed space prevents any smells from leaking into the home as long as the carbon filter is attached, the exhaust fan is on and the doors are kept closed.

Components like ducting and filters all reduce the capacity of your fan. You have to account for this in your calculation and get a fan that is more powerful, to make up for this reduction.

Other component like lights increase your cooling needs. You’ll want to add some capacity to account for those. If your tent is in a hot location, you should also add some capacity.

Here are common components and factors you should account for and the effect the additional capacity you’ll want to add, in terms of a percentage increase.

• lights: 10% increase for each grow light

• carbon filters: 25% per filter

• ducting: 1% for every foot of ducting

• bend in ducting: 30% per 90° bend (15% per 45° bend)

• external heat: 10% increase if your grow tent is in a warmer location (e.g. the attic or a sunny room) and/or is not well insulated from the external environment

Add all of the increases up to get a total percentage increase. For example, lets say we have a single grow light, one filter, and 6 feet of ducting with one 90 degree bend. But the tent is not in an especially hot location.

There’s two basic uses for a grow tent fan: intake or exhaust. Intake is drawing air into the room, often through a carbon filter to remove pests or unwanted dust/pollen. Exhaust is venting air back out of the room.

Most setups rely more on exhaust vents than intake ones. That’s primarily because removing excess heat or humidity is far more common than needing to force air into a space. Our recommendations today focus on exhaust needs, although these fans can also be used for intake if desired.

Passive air intake handles the majority of growing needs. As you push air out of a room, more is being pulled in naturally through any crevices or gaps. Along with it comes any dust, pollen, or contaminants which might be suspended in the air.

Active intakes such as using a fan are usually an expense most growers don’t need unless they’re trying to prevent pests or pollution from impacting their plants. They can be useful, and they can be paired with added CO2, but it’s a fine-tuning of an issue which isn’t necessary for all but the most particular of growers.

Speed controllers can be nice, but they’re not universally required. If your fan is at your desired CFM range, you’ll never really need to adjust it.

If you’d prefer to get a higher-powered fan than you need for your space (perhaps to have room for future expansions), a speed controller can be a benefit. You can use the speed controller to reduce your fan’s CFM from its maximum level to the range of your current needs. Later, when you expand to match your fan’s capabilities, the speed controller won’t be as necessary.

Final thoughts

First, we hope you made it this far and we didn’t bore you to death with our deep dive on fan types. Second, we want to congratulate you, whether you build your own grow room or not, the fact you’re looking to cultivate your own marijuana is commendable.

If you’re looking for commercial fans because you’re looking to start or grow a business, we recommend you check out our “how to start a cannabusiness” resource where we highlight some resources that can make the process easier.

If you’re just an average Joe looking to cultivate for your personal use and maybe for friends, then check out our “getting started growing cannabis at home” guide where, in a addition to fans, we provide a few other tips to help smooth out the whole process for you.