Ventilation In The Cannabis Grow Room: A Detailed Guide

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Added 12 April 2023

Cannabis is no longer the forbidden plant that you shouldn’t grow. As more and more countries legalize it, more and more growers are opting to grow cannabis in their homes, either as a hobby or a profession. 

But growing healthy, potent cannabis requires more than just sowing the seeds and waiting until the end of the season. Many things come into play to grow a healthy plant, one of which is proper ventilation — often overlooked. 

Ventilation is crucial for a cannabis grow room, regardless of the size. It helps manage the air quality, temperature, CO2, and humidity in the grow room, which further benefits your cannabis plant by boosting its growth and improving the potency and quality of yield. 

Without ventilation, expect the air to become stagnant and stale, stunting your plant’s growth and leading to other problems like heat stress, pest infestation, mold, or fungi. 

In this article, we walk you through the basics of ventilation for your cannabis grow room. The article explores the benefits of ventilation, factors that come into play, essential components you must have, and how to set it up per your preferences and goals. Read on to know more. 

Ventilation for Cannabis Plants

Ventilation for Cannabis Plants

For a new grower, the idea of ventilating their grow room may seem daunting, but that is hardly the case. The basics of ventilation are pretty simple — give your plant fresh air and remove the old, humid air from the room. 

But why do you need to do that — isn’t the air fresh in your room?

It’s unlikely, to be honest. There are a couple of reasons why the air in your grow room gets stale after some time. Let’s look at some of the factors why your grow room needs ventilation.

The first factor is transpiration, i.e., the sweating of plants. During this process, your cannabis plant sweats out water through the stomata in the leaves. By doing so, it creates a negative pressure within the plant that sucks up new water and nutrients from the soil and into the plant. This transpired water evaporates into your grow room, increasing the relative humidity. 

Another leading factor for stale air is your grow light system. All grow lights emit heat — some more than the rest. HID or HPS light panels are notorious for heating up too much compared to LED lights that run relatively cooler. 

So, when you run the grow lights for 12 to 18 hours daily, they are bound to increase the temperatures in the grow room. 

This is why keeping your grow room ventilated at all times becomes crucial. With the right ventilation, your grow room’s air stays fresh and clean at the right temperature and relative humidity. 

Depending on your room, you may either get away with a small fan or have to invest in an elaborate setup with intake and exhaust fans. More on this setup later, but essentially, ventilation is easy to do and can be quite helpful for your plants. 

Importance of Ventilating Your Cannabis Grow Room

Importance of Ventilating Your Cannabis Grow Room

But why is fresh air so important in the grow room? Because cannabis needs fresh air for one primary reason — photosynthesis. Fresh air is one of the main ingredients in efficient photosynthesis for your cannabis plant, allowing it to turn light, carbon dioxide, and water into food. 

The second reason is to breathe. Thanks to the respiration process, your cannabis plant can turn oxygen and glucose into energy, which helps the plant put on weight and grow juicy nugs. 

Similarly, your plant needs a lot of carbon dioxide to survive. Over time, carbon dioxide may deplete in your room if the air is stale, and your plant may suffocate. To prevent that from happening, ventilation becomes crucial in replicating the natural outdoor air. In addition, poor air circulation can cause CO2 to build up in one area while other areas have less than the required amount, leading to uneven growth and lower yields. Therefore, proper air circulation ensures that it is evenly distributed throughout the grow room. 

So, without fresh air or a ventilated grow room, your plant can potentially die by starving. It will find it difficult to handle processes like photosynthesis and respiration, which are crucial for the plant’s survival. 

Here are other reasons why ventilation is one of the most critical factors in your grow room:

  • Temperature and Humidity Control

Proper ventilation helps to regulate the temperature and humidity levels in your cannabis grow room. The ideal temperature range for cannabis plants is between 68°F and 77°F (20°C to 25°C), and the relative humidity (RH) should be between 40% and 60%. If temperatures or humidity exceed these ranges, it can stress your plants, resulting in stunted growth, leaf yellowing, or even death. Ventilation helps to maintain optimal environmental conditions for your plants by removing hot and humid air and replacing it with fresh, cool air.

  • Odor Control

Cannabis plants emit a strong odor during the flowering stage, attracting unwanted attention from neighbors or law enforcement. Proper ventilation helps to remove these strong odors from your grow room and reduce the risk of detection. Cannabis, after all, is a stinky plant; its scent is hard to miss. So, with proper ventilation with carbon scrubbers or filters, the pungent scent of cannabis can be subdued, ensuring the plant stays discreet and hidden. 

  • Pest Control

Good ventilation helps to deter pests and insects from invading your cannabis grow room. Pests thrive in warm, humid environments, so a well-ventilated grow room creates a less favorable environment for them to survive and reproduce. Pests can cause significant damage to your plants and reduce your crop yield, so you must take measures to prevent their infestation.

In addition, proper ventilation helps to prevent the buildup of stagnant air, which can attract pests. Adequate air circulation can help to keep pests at bay by preventing them from settling in one spot.

Another advantage is that ventilation helps control the spread of pests in case of an infestation. If a plant is infested with pests, the airflow created by ventilation can help to disperse the infestation and prevent it from spreading to neighboring plants.

However, ventilation alone may not be enough to prevent a pest infestation. In case of an infestation, you must take additional measures to eliminate the pests. 

  • Improved Yield and Quality

Proper ventilation leads to healthier, happier plants that produce higher yields and better-quality buds. By providing optimal environmental conditions, including the right temperature, humidity, air circulation, and CO2 levels, you can ensure that your plants are growing to their full potential. 

While most grow guides call for high-end grow lights and other peripherals, many growers take ventilation for granted. But if you invest a little time and effort in this setup, you will be rewarded with a healthier plant. 

Crucial Components of Ventilation for Cannabis

Crucial Components of Ventilation for Cannabis

An ideal ventilation system must accomplish a few tasks to keep the air fresh within the grow room. For example, it must keep the air flowing at all times to keep humidity and temperature levels in check. 

Next, it must push out the old air and intake new air into the grow room. This will help keep CO2 levels in line, replicating outdoor air. The same system must also filter the intake air so it is clean and free of harmful pathogens or pollutants that may harm your plant. 

Many growers may even use filters or scrubbers to mask the smell of cannabis. But these are just the basics. Let’s look at these components in detail and how to use them.

1. Extractor Fan

As the name suggests, an extractor fan extracts or pulls the air out of the grow room. Since hot air is lighter, it rises to the top of the grow room, so an extractor fan must be placed near the ceiling to pull out hot air. 

But there are countless options for extractor fans on the market, and you must choose one that fits your growing space. For this, you need to calculate the CFM of your grow room and choose a fan with similar ratings. More on this later. But ideally, you should pick an extractor fan with at least 40 CFM.

2. Carbon Filters

As mentioned earlier, cannabis is aromatic, but not everyone appreciates it. So, to mask its smell, you need carbon filters. Carbon filters are a vital component in a cannabis grow room ventilation system. They remove unwanted odors and gases from the air, keeping the grow room environment clean and fresh.

Carbon filters work by using activated carbon — a type of carbon treated with oxygen to open millions of tiny pores between carbon atoms. These pores create a massive surface area that can attract and absorb unwanted gases and odors from the air passing through the filter.

As the air passes through the carbon filter, the activated carbon absorbs the unwanted molecules, trapping them within the carbon pores. This process effectively removes the odor and gases from the air, resulting in cleaner and fresher air exiting the filter.

That said, choosing the right size and type of carbon filter for your grow room is essential. The filter size should match the CFM rate of your exhaust fan, ensuring that all the air in the grow room is being filtered effectively. 

However, remember that you’ll need to replace carbon filters periodically. This is because the activated carbon will become saturated over time and lose its effectiveness. Carbon is a dense material — a single gram of it has a 3000 m. sq. surface area — so even smaller carbon filters are terrific at masking the smell of cannabis. 

3. Fans

Carbon filters are optional but fans are essential in all ventilation systems for cannabis grow rooms. This is also the most common equipment that all indoor growers must use regardless of their grow room setup. 

Even a small motorized fan works wonders for a grow room with a low heat signature. But the bigger the setup, the bigger or more fans you would need. For example, for a large grow room with multiple plants, you would have to set up multiple fans to keep the air circulating, but a small computer fan is enough for a space bucket setup. 

You must also use fans for the exhaust and inlet to push out the old air and bring in new air. The fans will work together to keep the air fresh and regulate temperature and humidity. 

If you want to go a step above, you can choose dedicated gardening fans with built-in humidistats and thermostats, which automate the process so you don’t have to worry about anything. 

On the other hand, some growers may even try oscillating fans as an add-on. These cheap, rudimentary fans work wonders in keeping the airflow fresh in the grow room. Plus, their airflow can even help strengthen the branches of your cannabis plant!

4. Air Conditioner

You may also need to invest in an air conditioner, particularly a mini-split unit. These devices are efficient at managing heat and humidity in the grow room, and compared to most other ventilation devices, ACs give the most control to you. 

Although ACs can’t increase ventilation directly, they can indirectly increase ventilation in a grow room by helping to regulate temperature and humidity levels. When the temperature and humidity in a grow room are too high, it can cause a lack of oxygen and a dramatic increase in carbon dioxide, negatively affecting plant growth. By cooling the air and reducing humidity, an AC can create a more favorable environment for plants, indirectly improving ventilation.

However, it’s best to use an AC in conjunction with other ventilation equipment, such as exhaust fans and air filters, to create a more efficient airflow. This is because an AC is not a substitute for proper ventilation. For example, you can use the AC to cool the air, while an exhaust fan can be used to remove stale air and replenish fresh air. You can also use air filters to remove odors and airborne contaminants, ensuring that the air entering the grow room is clean and fresh.

If you plan to invest in an AC, just pay attention to the conditioner’s BTU (British thermal unit), which measures the amount of energy used by an AC in order to remove heat. Think of it as a way of measuring the efficiency of the conditioner. 

Choose a conditioner with a BTU that matches your grow room’s volume. Use this online calculator to figure out the ideal BTU for your grow room. 

5. Air Coolers

An air cooler can increase ventilation in a grow room by increasing air circulation. Air coolers blow air over a cooling pad or evaporative media, causing the water in the pad to evaporate and cool the air. The cool air is then blown out into the room, increasing air circulation.

Like air conditioners, air coolers can also be used with other ventilation equipment, such as exhaust fans and air filters, to create better airflow. 

However, remember that air coolers work best in dry climates with low humidity. An air cooler can increase humidity levels in humid climates, leading to mold and other moisture-related problems. In addition, air coolers may not be as effective at cooling the air as air conditioners and may require more maintenance to keep the cooling pads clean and functioning properly.

Other Important Factors for Ventilating Your Grow Room

Other Important Factors for Ventilating Your Grow Room

Apart from the devices mentioned above, you must also focus on a few other things when setting up the ventilation for your cannabis grow room, such as the fan size, passive intake vs. active intake, and negative air pressure. Here’s more on them.

1. CFM and Fan Size

One important factor is choosing the right fan size for your grow room based on your room’s CFM. Remember, the goal is to bring in as much air as you take out of the grow room, so the fan size plays a crucial role. The right size ensures your fan is efficient enough to replace the air. 

Also, this exchange must happen at least once a minute. Depending on your setup, your fans may also need to replace the air 2 to 3 times per minute, especially if you are using grow lights that heat up a lot, you live in a hot region, your plant is growing in the loft or basement, or you use CO2 supplements. 

For this, you need to begin with the volume of your room. Using the volume, you need to pick the right fan size for your grow room. For instance, if the grow room is 10 cubic meters, you would need a fan that extracts at least 10 cubic meters per minute or more, depending on your grow room conditions. 

But you need to use imperial metrics here. So, instead of meters, convert the metrics of your grow room from meters to feet. Taking the same example as above, the 10 cubic meter room would be 353 cubic feet. Then the fan needs to replace the air at 353 cubic feet per minute (CFM) or more. 

Remember, the volume of your grow room isn’t the only aspect that comes into play when choosing a fan size. You also need to factor in other aspects like the ambient temperatures both inside and outside the grow room, season, location of your grow room, etc. However, CFM is a good starting point for new growers. 

2. Passive Intake vs. Active Intake 

Air intake refers to the air your fans pull into the room, but there are two ways to do this — passive and active. With passive intake, the air naturally flows into the grow room via vents. On the other hand, active intake relies on fans to pull air into the room. 

For most growers, the ideal way to bring more air into the room is to use active air intake, which is efficient and reliable. But if you are only growing one small cannabis plant or have decent airflow, you can get away with passive air intake. 

3. Negative Air Pressure

While ventilating your grow room, you need to replicate the outdoor air flow in your grow room. To make this happen, you want to maintain negative air pressure in your grow room, where the air leaving the room is more than the air being sucked in. 

By having negative air pressure in the grow room, it gets easier to manage the airflow as well as temperature, relative humidity, and carbon dioxide levels in the room. Plus, the cannabis smell does not build up in the room. 

You can maintain negative air pressure in your grow room by ensuring the intake fan has a slightly lower CFM level than the exhaust fan. 

  • Carbon Filter and Extractor Configurations

As mentioned above, you can configure the carbon filter and extractor in various ways, depending on your goals and conditions. Here are a couple of common configurations for the same.

  • Carbon Filter - Extractor - Exhaust 

The most common way is to configure the carbon filter - extractor - exhaust. The benefit of this configuration is that the air is scrubbed even before it reaches your fan and ducts. But this configuration has some downsides — this setup takes up a lot of space and is not ideally suitable for smaller tents or grow rooms. 

  • Carbon Filter - Lighting - Extractor - Exhaust 

If you have an enclosed ventilation system on your lights, you can even install the carbon filter before the lights and the other two after. This makes the entire setup easy and compact but is only ideal if you have a lighting system with enclosed venting.

  • Extractor - Exhaust - Carbon Filter

Lastly, you can simply place the carbon filter after the exhaust. This is an easy setup for most growers, especially if the space is limited, as you can install the filter outside the tent or grow room if required. 

How to Set up a Ventilation System for a Cannabis Grow Room?

How to Set up a Ventilation System for a Cannabis Grow Room?

Now that you know all the basics and necessary components of a proper ventilation system for your grow room, it’s time to put it all together. So, follow these steps to set up the ventilation for your cannabis plants. 

1. Choose Your Fans, Carbon Filters, and Other Devices

The first step is to get your hands on a few exhaust and intake fans, depending on the size of your grow room. Choose the fans as per the CFM of your grow room and ensure the intake fan’s CFM is slightly lower than that of exhaust fans to ensure negative air pressure. 

Next, you need to get a carbon filter to scrub the smell of cannabis from the air. This is optional; if you don’t have to worry about masking the smell, you can skip this step. You can also invest in controllers for the fans and devices to have centralized control of the fans. Choose smart ones that even allow automation. 

2. Install the Exhaust Fan and the Filter

The next step is to install the exhaust fan and carbon filter. As mentioned above, you can configure this setup in various ways, so choose the one that suits you best. To hang them, you can use tape or clamps to hold the fan and filter together near the ceiling

Position the outlet wherever you want to let out the hot air and use ducting to direct the air outside the space. Also, ensure there are no air leaks in the configuration. Otherwise, the old air will not escape efficiently. 

3. Install the Intake Fan on the Opposite Side

Once you have installed the exhaust fan, you can install the intake fan, ideally on the opposite side of the grow room near the floor. Doing so will ensure efficient air movement from the bottom to the top and across the grow room. 

Like the exhaust fan, you can hold the intake fan in place using clamps or tape, whichever works for you. You may also want to install a bug screen before the intake fan to keep contaminants and pests out of the grow room. 

4. Position the Oscillating Fan

If you’re using an oscillating fan, now is the time to position it. You will be leaving the fan on 24/7, but it must also blow a slight breeze on the plant. Position it accordingly but don’t let it blow your plants away. 

That’s it. Your grow room ventilation setup is ready. But this is only a basic setup. Depending on your goals and preferences, you can add many more devices and peripherals, such as a thermostat, air conditioner, sensors, automated controllers, etc. 

Whichever device you add to your grow room, do enough research to ensure it is adequate for your grow room while not overpowering other devices. 

How to Ventilate a Micro Grow?

How to Ventilate a Micro Grow?

If you’re growing cannabis using micro-grow techniques, a basic ventilation system will suffice. Once your tent or cabinet is ready, use a small oscillating fan and, if required, an exhaust fan to keep the air flow fresh. 

In a micro grow, you won’t face significant issues like heat or high humidity since your lighting setup is rudimentary. But even if you have to manage any of that, a small extra fan or a small dehumidifier can be enough. 

How to Ventilate a Greenhouse?

How to Ventilate a Greenhouse?

If you are ventilating your cannabis greenhouse, you don’t have to worry much. Most greenhouses have flaps that can be opened or closed, acting as vents. But if your greenhouse lacks those, you can keep the door slightly open or remove one of the panels. 

But for a bigger greenhouse, you may need to set up a proper ventilation system with inlet and exhaust fans, carbon filters, etc., as mentioned earlier. 

Additional Tips to Increase Ventilation in the Grow Room

  • Use oscillating fans

Oscillating fans can be used to improve air circulation in your grow room. They help to prevent hot spots and create a gentle breeze that can strengthen plant stems and promote healthy growth.

  • Install ventilation windows or vents

Ventilation windows or vents can be installed to allow fresh air into your grow room. You can control them manually or automatically and create a more natural airflow.

  • Use air-cooled lighting

Air-cooled lighting systems can help reduce your grow room's heat output. By drawing cool air from the outside and passing it over the lighting fixtures, air-cooled systems can help to keep the air temperature in your grow room within an optimal range, reducing the need for high-powered exhaust fans.

  • Optimize the layout of your grow room 

The layout of your grow room can also affect ventilation. Thus, placing your intake and exhaust fans in strategic locations can create a more efficient airflow. Placing your fans at opposite ends of the room can create a natural convection current that can help to move air more efficiently.

  • Clean grow room regularly

A clean grow room is essential for optimal ventilation. Dust, debris, and plant material can clog filters, reduce airflow, and promote the growth of harmful bacteria and pests. Regularly cleaning your grow room can help to improve ventilation and make your plant’s life easier. 

Summary: Ventilation In The Cannabis Grow Room: A Detailed Guide

In conclusion, this guide highlights the importance of proper ventilation for a successful cannabis operation. With it, you can ensure your plant always gets fresh air, optimal humidity, and the right temperatures. All of which are crucial for photosynthesis and respiration. Ventilation also helps prevent other issues like pests, mold, or fungi, which thrive in humid conditions of stale air. 

Always choose high-quality equipment for your ventilation setup and remember the motto — you must replace old air in your grow room with fresh air at least once every minute while maintaining negative air pressure. 

And if you are worried about someone finding your cannabis plant, you can use carbon filters in your exhaust setup to scrub the smell of cannabis before the air is exhausted. It is worth the investment as it can save you a lot of trouble if you are growing cannabis where it’s not decriminalized. 

The end result would be a healthier plant with a much better yield than you would have expected.



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