How To Set Up Ventilation Systems for your Cannabis Grow

In this piece we will study how use your ventilation system to create the perfect conditions for your plants. For your hydroponic systems to prosper you will need fresh air, ventilation and exhaust air set up properly. Naturally your plants would grow in a soft breeze and warm climate. When growing indoors you can create an environment that caters to the needs of your plants perfectly.

Light, water and air are the main factors for the growth of your plants and therefore your business. You are going to want to set up these systems with great care because they largely determine your production. Ventilation will allow the plants to be supplied with CO2 for growth as well as regulate the temperature of your grow tent or room. Better climate means better plants means better yield!

Air Circulation and Temperature for Indoor Growing

The perfect temperature will help your plants to grow. Too much heat is a source of major damage for your plants and might cause heat burn or weak plants. The temperature you are looking for is between 75 and 85 degrees F. Never go lower than 64 or higher than 86 degrees.

Pro Tip 1

Get a thermometer!

The main source of heat for you will be your lights. Through fans in the room and an extractor fan system you can make sure that the temperature stays stable throughout the entire area. Extractor fans will pull the hot air out of your room and pump in fresh and cool air. A fan within the room will regulate the airflow when growing weed indoors.

Since hot air will rise to the top of your room you want the extractor fans to be placed close to the ceiling or on the top of grow tents.

For grow tents, as a rule of thumb you should use one 6’’ exhaust fan when starting out with one grow tent. The size 4’’, 6’’ or 8’’ describes the diameter of the fan. 6’’ seems to be the standard for most air-cooled hoods and is therefore recommended. 

For a grow room you want to use roughly one exhaust fan for every foot of room.

Make sure to buy an exhaust fan that suits your needs. The products will be labeled with "cubic feet per minute" and you should be looking for the exhaust fan or number of fans that can circulate the volume of air in your entire space. Do the math to determine the volume of your growing space by multiplying length, width and height of your room for indoor growing. 

If your room is more hot or more humid you may choose an exhaust fan with a higher cubic feet per minute performance. It is always easier to reduce the speed of the fan or turn it off when the capacity is too big. But there will be often times when it comes in handy to be able to move a lot of air, e.g. during a heat wave, so err on the side of excess capacity. Ultimately, you'll want to test and learn into the right amount of ventilation needed -- so don't be afraid to experiment and let the thermometer be your guide.

Pro Tip 2

An exhaust fan with filters is extremely important. The filters will help you to control the smell of your marijuana production. Use a carbon filter to eliminate the smell!

To move fresh air inside your growing facilities you may use an active or passive intake. An active intake is an intractor fan that pushes air into your grow room. Passive intake is basically a hole. If you create a negative airflow within your space through the exhaust fan the hole will automatically suck in fresh air to balance the pressure.

If you're growing in a grow tent, be sure to get a good inline grow tent fan that you can hook up to 6" ducting to properly vent your grow tent.

Pro Tip 3

You will want to add extra oscillating fans to circulate the air in your room so that every plant in your hydroponic systems is reached. Your plants enjoy a natural breeze and will reward you with stronger stems because they will bend and move just like in nature.

Oscillating fans can dry up the top part of your plants' container, therefore making them less attractive for fungus or pests to settle in. The artificial breeze they create will take away the moisture of the plant’s transpiration as well as the humidity created by you watering the plants. This will significantly reduce the chances of your plants getting white powdery mildew, bud rot or mold. Small fans are cheap and you can even use them in big areas.

Pro Tip 4

Don’t blow your oscillating fans directly at the plants. Have a breeze from above or under your plants. Too much wind might damage the leaves. You will recognize leaves that are hurt by wind because they look like "claws".

Next to the fact that you want your plants to stay cool and dry you will want to make sure that your plants receive enough CO2 (carbon dioxide). CO2 is what the plants live off of and what they use during photosynthesis to grow. Some growers even artificially inject CO2 into the grow room to increase yields. If you want to use extra CO2, place the system above your plants as well, as CO2 is heavier than air. Only inject CO2 when working with a sealed space.

The ventilation system will largely determine your output when indoor growing. Consider the ramifications of this when setting up your grow room for cannabis cultivation: This might mean extra room for extractor fans and oscillating fans as well as additional costs. Also you might need more power outlets or a better electric system. These investments will pay off with healthy plants and a better yield.

Climate and Humidity when Growing Weed Indoors

When growing in a closed room humidity in the air and in the soil will start to build up. Keep in mind that being too wet might cause fungus or mold for your plants. It might even cause random problems like issues with rooting, bud rot or spider mites.

For your plants to stay strong and healthy you might want to consider a dehumidifier which will extract the water out of the air. This can lead to your plants growing faster and stronger than you ever thought.

Pro Tip 5

Keep humidity the highest (ca. 85%) when cloning, keep it medium (ca. 65%) in vegetative stage. Keep it low (ca. 45%) in the flowering stage.

Find our corresponding article on how to water your plants.  

Hydroponic Systems with Better-than-Nature Conditions

Air circulation might not be your first concern when starting out. But it will make the difference between a hobby and a professional grower. The better the environment you create for your plants - the better your yield.

Bonus: Make sure that the air of your sealed growing space is passed through a carbon filter when using an exhaust fan. This will eliminate the smell.

Hydroponic systems have a few key performance factors. Next to light and water, air flow, temperature and humidity are the ones who will make or break your production. So let your plants enjoy a gentle breeze whilst you enjoy your yield.


1 comment

  • Hello! Good Evening.

    Is there a correct measure of air flow per m2?
    How can I tell if my flow is correct?
    The temperature and humidity are perfect!

    Thank you.


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