Ventilating Your Grow Room

Use Oscillating Fans

Your grow room is going to need two types of fan systems. The first one is an oscillating fan. these are effective and cheap fans and have great qualities. They will help blow they are under, above, and around your marijuana plants. This helps improve air circulation and it keeps the grow room cool.

One of the best parts about these fans is that they’re easy to move around as well as set up so you can experiment with different placements of the fan so you can find the right location. You want your oscillating fan to reach every area of the grow room so you might have to invest in a few extra fans. One thing that you do want to do is to make sure did the fans are not pointing directly at the marijuana plants. If they are pointing directly at the plants they could suffer windburn and the plants could be damaged.

By setting up your oscillating fans you’re going to moderate the humidity and the temperature of the room. You will also need an air extractor fan system to do this as it helps to keep the air fresh. Here’s what you need to know about an air extractor fan system.

Air Extractor Fan System

When you use an air extractor fan system this is going to cycle out the old that is in the room and bring in the fresh air. This is going to help the plants thrive and grow properly. You want the fan system to replace the air in the room every minute or at least every few minutes. You’re going to need it the right fan size. Having proper ventilation is going to be one of the best choices you make for growing your plants. You should have all of this set up when you were starting so you don’t have to run around and try to set it up in the future. Plan everything out before you begin and it’s going to be much easier for you.

Calculation of the Fan Strength

You will need to do a bit of mathematics to figure out the fan strength you’re going to need. This is quite simple to do. Your fan is going to be rated by cubic feet per minute or CFM. to figure out the CFM you will need to do the following:

  • Know the dimensions of the grow tent or grow room
  • Know the efficiency of the exhaust

To calculate the volume of the grow room you want to multiply it by the length times the width times the height. this is going to give you the cubic feet measurement of the room. Write this number down and then you’re going to multiply this by the efficiency drop.

Efficiency will vary based upon the make of the filter, age of the filter, and the length of the duct which is between the filter and the fan as well as other factors. At the minimum, you want to multiply the room volume by 25%. if you have a long dark path you can multiply this by three and if there is a short path you can multiply it by two.

your formula works out as follows:

The volume of the room X the efficiency drop equals your CFM.

If you have a room that is 320 cubic feet for example, and there is a short duct then you going to multiply this by 2. This formula would be 320 times 2 equals 640. This will give you your CFM so you need a fan that is higher than this number.

Active Intake Versus Passive Intake

You can bring air into the room in two different ways. You can use an active intake or a passive intake.

A passive intake is going to rely on negative pressure and passive air flow. When you use this ventilation system for your grow room then there’s going to be a fan blowing air out but no fan blowing air in. There will be an intake hole that will passively allow new air to come into the room. This works because of the pressure differences between the air outside and the air inside the room.

For this system to work you have to ensure that the intake hole is around three to four times longer than your exhaust hole. This is going to prevent the fan from overworking and the ventilation system will have the right suction. You can also create more than one passive intake hole.

When you use an active intake system this is going to draw air into the room with a fan system. You will have one fan blowing air into the grow room and another fan blowing air out. The size of the intake hole really doesn’t matter if you use this sort of system. If the intake hole you have is the same size as the outtake whole then this is a good system for you to use.

Humidity Control

Plant health is impacted a lot by humidity. If you have too much humidity then there could be disease present in the grill room and if there’s not enough then this can impact growth in a negative way. You want to always measure your humidity.

Humidity is usually caused by transpiration in the grow room. Transpiration is a process in which the leaves of your marijuana plant will give off water into the atmosphere. This works like a straw does because the suction which is created by transpiration will pull nutrients through the marijuana roots as the plant is producing water vapor.

Your plants will stop growing if they happen to dry out. When you deprive them of water they become starved of nutrients. On the other hand, if there is too much humidity in the grow room. Then pests and diseases can develop and this will also prevent evaporation. If there is not enough evaporation in the plant can’t perform transpiration. You need to be able to both lower and raise the humidity in the grow room easily to ensure that the plants are healthy.

To lower the humidity is a simple process. You want to vent the humid air out of the room with an exhaust system. If the air from the intake system is less humid than the air inside the grow room you can use a dehumidifier. during the growing process, there might be times when you also need to raise the humidity. You can seal up the grow room or turn off the exhaust system temporarily and this will raise the humidity quickly in the room. Make sure you do some research into the crops you’re using in the humidity level that they prefer and try to stay within this range. A larger plant will be producing more water vapor than smaller plants do so as the plants grow you will have to pay more attention to the humidity levels.

Injection of CO2

The plants are going to require CO2 for the transformation process. You can usually do this by injecting CO2 into the grow tent. Here are a few things you need to understand about CO2.

You will need a sealed grow room before a CO2 injection. The first reason that you need to do this is that you want efficiency. CO2 only works at a high level so you need the girl room to be sealed so you get a high enough concentration so everything works effectively. You also have to consider safety because the high levels of CO2 recommended for your plans are going to be dangerous to you. It’s not a good idea to have a lot of CO2 leaking into the home because it can put you at risk.

Before adding extra CO2, you also have to have bright grow lights so the plants can take advantage of the CO2. Strong LED lights or MH/HPS are recommended because they will produce the light that you need. T5s or FLs aren’t recommended because they usually don’t produce very good results.

Once all aspects of the gross system have been optimized then you can add CO2. It will work best if the entire environment has been optimized. If you don’t have a larger budget or you’re happy with the yields you have already then you might not need CO2 injection. If you have some room in the budget and you want to experiment with your crop yields then CO2 injection can work for you. A little bit of research into CO2 injection will help you out.


FAQ For Grow Room Ventilation

What type of fan should I be using?

There are many different choices when it comes to fans. You will need an in Duct Fan that is greater than the CFM you have calculated for the grow room. Once you have your fan specifications then you need to choose the right model. Make sure you read product reviews because fans will vary in their price range. You may also need to pick up a filter for your fan although some fans do come with them.

 How large of a fan do I need for my bulb?

The size of the bulb will help you narrow down your fan choice. You can usually get fans that come in 4 to 8 in diameters. You’ll probably want a 6 in diameter fan because of the opening of the light hood. The opening is usually 6 in but make sure you measure this to be sure.

How big should the fan be?

We’ll have to calculate the CFM of the room using our formula we created. This number is going to help you find the right fan that is going to work for your individual setup.

How large should the intake fan be?

The size of the Arctic fan in the system you were using or going to be the factors which will determine your intake fan size. If you’re using a passive intake system then you don’t need an intake fan. If you’re using an active intake system then you want a fan that has the same size as the outtake fan.

Can you explain negative pressure?

When the pressure inside of the grow room is less than the pressure which is outside of the room this is negative pressure. During passive intake, this principle comes into play. The negative pressure which is inside the room will pull the clean air from the outside environment through your intake hole.

Think of it this way, negative pressure is like a journey beneath water which is in a plywood box. As it is sinking water will come rushing into the box because the pressure which is inside the box is going to be less than the pressure of the water which is outside of the box. You can pretend that the water which is rushing in is clean air and that the water which is leaving in the bubbles is the dirty air. This is how negative pressure works.

What about ducting?

For most grow systems aluminum ducting that is flexible will work well. This is easy to install and quite affordable. You can also use insulated aluminum ducting or you might prefer a heavy duty duct this will all depend upon your budget and individual preferences. When you have a smaller duct, this creates greater airflow resistance. the length of the duct and the bends in the duct also create a greater airflow resistance. The air flow reduces the further the air has to travel.

How can the ducting be improved?

If you’re using flexible aluminum ducting, you should smooth out all of the wrinkles. This improves the performance of that ducting and increases the airflow. You can also try to reroute the docked so it makes fewer turns along the way. If possible, try to shorten the length of your duct system.


It can be complicated to find the right ventilation system for your grow room. You need to understand how ventilation works as an indoor grower. Grow room ventilation systems have a lot of benefits so understand the basics so you have the right system for your grow operation.