Make Sure To Have Plenty Of Fans Your Grow Room: Find Out How Many

Grow Room Fans

An integral part of designing your grow room is establishing proper ventilation. For many reasons, sufficient ventilation is critical for growth, particularly if you take your harvests seriously.

For one thing, if there is no humidity and temperature control, a quality harvest is not going to happen.

How many fans should a grow room have? At least two fans: an extractor fan and an oscillating fan. These fans are the bare minimum for growing marijuana. But, if you have bigger operations, then you might need multiple fans. You will need an exhaust fan to operate.

Beginners sometimes disregard the importance of air when growing herbs, or any other plants, for that matter.

This article focuses on the importance of proper ventilation. As we go along, you will learn how to install fans.

Why Proper Ventilation Matters

Giving your plants a better growing environment than outdoors is the main focus of a growing room. It also means providing fresh air that is CO2-rich.

A ventilation system is critical to keeping optimum levels of CO2 content. Because the atmospheric CO2 concentration is low, a constant flow of fresh air from the outside is necessary.

Plants are exposed to the wind and elements while growing in the outside weather. Being deprived of these conditions can affect them in unexpected ways. This is why proper ventilation matters when growing indoors.

In the wild, cannabis plants love a nice breeze and fresh air. Lucky for you, you can control the air circulation when growing cannabis indoors.

You can use exhaust to create the perfect indoor environment that mimics the best parts of nature.

Among the reasons why you need proper ventilation is to ensure the quality of your crops. Here, we list the reasons why ventilation in this kind of setting is crucial:

1. Better Air Circulation

Air circulation is a crucial ingredient for creating a perfect growing environment for your cannabis.

Indoor growers aspire to create a better-than-nature environment for their crops. The way air moves will have a surprisingly big impact on how your plants grow.

2. Control the Level of Humidity in Your Grow Room

If you have plants that didn’t grow the way you wanted them to, then you did something wrong.

The possibility is that your grow room could have had uncontrolled humidity. The quality of the plants you’ll grow has something to do with this.

3. Get the Ideal CO2 Level

When it comes to the growth of your plants, photosynthesis is everything. Your plants won’t have enough carbon dioxide if you leave your growing tent closed without ventilation.

Your plants will wilt without CO2 and eventually die. Your ventilation setup will help your plants get the amount of CO2 they need.

Your plants or crops will grow healthily with sufficient CO2. If your growth room doesn’t have enough CO2, photosynthesis will be compromised.

4. Avoid Pests and Plant Diseases

Improper ventilation can lead to diseases or pests that you don’t want your plants to get. Once this happens, you will regret not scheduling your ventilation system!

With poor ventilation, pests and plant illnesses will happen. Mold, mildew, fungus, and other threats are the most common illnesses your plants might get.

These are pests and diseases that thrive in humid areas. As some of them are difficult to detect, this could be a big issue.

5. Strengthen Stems

A nice breeze strengthens stems by allowing them to bend and sway as in nature. It increases the stem strength, which is useful when plants begin to get large and heavy from the bud.

A fresh breeze enhances the stalks and stems of cannabis plants in the growing space.

6. Lessen Heat and Wind Stress

In an indoor grow room setup, heat is unavoidable. Remember that you will be using grow lights as your indoor sunlight.

Whether you’re using ordinary growth lights or LEDs, all of them will generate heat.

Your plants will wilt and die of heat if there is no ventilation system in your growing tent.

Constant air circulation in your grow tent will decrease the heat intensity.

When to Install a Ventilation System

If you have an established indoor grow space, in all likelihood, you will need a ventilation system of some kind.

By indoor grow, I mean a closed setup within four walls. A ventilation system is required if there is no obvious entryway for air circulation.

A ventilation system for indoor grows must be tailor-made for the grow rig.

The heat and humidity conditions of the plant variety being grown have to be taken into consideration.

The current structural ventilation systems, such as grilles, vents, or ducts, are not good enough.

You will integrate these into your setup, but you will still require strategically positioned fans.

Better Grow Room Ventilation

Extractor Fan

Extractor fans suck out the old air from your growing space. Because hot air naturally rises, your extractor should be mounted at the top of your room/tent. Any growth lights or reflectors come with an exhaust system connection.

Bear in mind that there are several different extractors on the market. You will need to match your extractor’s capacity to your grow space’s scale.

Usually, indoor extractors’ strength is estimated in CFM or cubic feet per minute.

Understanding CFM: Multiply the length, width, and height of the grow room to measure the volume (ideally, in feet).

Oscillating Fans

Although easy and inexpensive, strategically positioned fans can appear to facilitate effective airflow around your rising space.

Not only will the wind reinforce your plants’ roots, but it will also help prevent stagnant air from piling up around your room.

This will minimize the chance of pests or plagues destroying your crop.

Carbon Filter

Carbon filters scrub the pollutant in the air of a grow room. They even absorb the terpenes given off by your plants when connected to your exhaust system.

The purpose of this is to clean the air from your growing space. Because carbon is very thick, activated carbon filters effectively deal with the cannabis smell in the grow room.

Passive vs. Active Intake System

Passive Intake

A passive intake means you’ve just got a fan blowing out dirt and an intake hole to let in the fresh air.

With a passive intake, you have no intake fan to help pull in the fresh air.

Here are things you need to remember:

  1. The intake hole should be three to four times wider than your exhaust hole for each passive intake. The purpose of this is to achieve sufficient suction. It will also keep your fan from trying so hard to pump out air that it cannot replace.

  2. With more than one passive intake hole, more air can come in. The holes for fresh air to flow in should be larger than the hole where the air is being forced out.

Active Intake

An active intake means that to get air into the tent, you use a fan. So, you also have a fan at your intake hole, in addition to your exhaust fan, blowing air in.

It is unnecessary to have a big intake hole because the intake fan can help replace the air. If your intake hole has the same size as your exhaust hole, consider this intake.

Determining the Fan Sizes for Your Grow Room

1. The Volume of Your Grow Room

Volume is essentially the size of the three-dimensional space accounted for by your bed.

So, simply multiply the length, width, and height to calculate the volume of your room.

A room will have a capacity of 350 cubic meters, which is 5 feet long by 7 feet wide by 10 feet tall.

The word “cubic” simply means that the volume of a three-dimensional space is defined by the integer.

2. CFM Requirements – The Air Exchange Necessary

Exhaust fans are typically rated in cubic feet per minute, or CFM, or the volume of air pushed.

Ideally, you want a ventilation system that can swap air at a minimum of once every three minutes.

Divide the amount of your room by 3 minutes to decide what your CFM specifications are.

So, we will divide 350 cubic feet by 3 minutes to generate an amount of approximately 166.67 CFM. Therefore, the bare minimum required is 166.67 CFM for an exhaust fan in this space.

Other Considerations and Variables

I just helped you measure the MINIMUM CFM needed to ventilate your growth space.

These equations fail to take into account other considerations that may influence how much ventilation is required.

Almost definitely, you will need more airflow than what you find in phase 2, so don’t fail to consider these.

  • Temperatures – If your grow room runs hot, you will need to add up to 25% of the CFM you measured earlier. Hot and humid climates can require up to 40% more than the previously estimated CFM.

  • HID Lights – Growing hot lights such as HPS lights and metal halide lights increase the amount of ventilation needed. Once the formula mentioned above has determined the CFM required, add 5% of that amount for each air-cooled HID lamp. You will need to add 10-20% to each light for non-air-cooled lights.

  • Filters – If your exhaust system uses a carbon air filter, you must prepare for the system’s vibration. If you are using a carbon air filter, apply 20% of the cumulative CFM measured in the three phases above.

Placing Fans in the Grow Area

Most indoor weed farmers use fans to blast air around the grow room. It provides the breezy feeling that cannabis plants enjoy.

  1. Do not point a strong fan directly at a plant. Too much wind can harm the leaves and stems.

  2. You want a nice breeze around the main canopy. This means you want air to blow above and below the plants.

  3. Small oscillating fans are great for the growing space because they are inexpensive and can provide a nice, gentle breeze, even in a relatively wide area, without blowing on any one part too long.

  4. After placing fans, check around the growing area to ensure that all parts get a slight breeze. You may want to change the fans if you notice stagnant air or a lack of air or wind.

Time to Give Your Grow Room Proper Ventilation

  1. Set up your fan and filter – Get your carbon filter installed, followed by your exhaust fan. Before you install your grow lights, we recommend installing both, as setting up ventilation around your lights can be tricky.

  2. Put up your grow lights – Use rope ratchets to install your lights once you’ve installed your filter and fan.

  3. Connect everything – Connect everything using ducting once you have everything installed inside your tent. Utilize ducting clamps to hold everything in place. Also, keep some duct tape handy to cover up any tears in your system.

  4. Pull more ducting – Use ducting outside your tent to bring air to a window from your fan. To maximize efficiency, keep the ducting path as straight and short as possible.

  5. Use active or passive intake to draw new air into your tent – Remember to make sure the intake vents in your tent are open if you rely on passive intake. Keep a window open near your grow room, too. This will help replace the vented hot air from your tent. Install your intake fan at your tent’s intake vent if you are using an active intake.

A Few Tips for Growing

  • Get a thermometer – Your lights will be the principal source of heat. This will ensure that the temperature remains constant in the whole room using fans and an extractor fan system.

  • Humidity – When cloning, retain humidity at its peak, 85%. Keep it medium, 65%, in the vegetative stage. In the flowering stage, keep it down to approximately 45%.


One often-underestimated notion is the location where air should enter your grow room.

It will be largely ineffective to run an exhaust fan without any place for new air to enter your growing room.

At best, to try and push out air that simply isn’t there, your fan will struggle and overwork itself. Your fan will not be able to bring new air into the room and will simply circulate air around without help.

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