Your garden's atmosphere affects your plant's health to quite an extent. If you didn't know that already, here's a guide to help you understand the nitty-gritty concerning a grow room's atmosphere more profoundly. – Gro Indoor
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Things You Need to Know About Grow Room's Atmosphere and Ventilation

by 09 Apr 2023

Things You Need to Know About Grow Room's Atmosphere and Ventilation

Just as enough sunlight is crucial for a plant's overall growth, your garden needs to have just the right atmosphere and ventilation system to grow healthier plants. Taking in the fresh air and exhaling waste air and heat in the grow room positively affects your plant's growth.

Most growers would agree that their garden's environmental condition plays a major role in growing better crops. Sometimes, even more than a grow light does. That is, sometimes, a grow light doesn't provide sufficient lighting to the garden. While this can halt a plant's growth, if your growing area has the right atmosphere, the repercussions wouldn't be much. For this, you need to have the right setup in your grow area. Similarly, with a quality grow light without the right environmental settings, your growth can come to a standstill.

Let's dig deep into the subject and find out how your garden's air can affect your overall yield. But before we start, let's consider the design of the grow room.

Grow Rooms (Open Loop)

In open-loop grow rooms, your plants get a constant supply of fresh air. There are two ways; an open-loop grow room supplies fresh air to the plants. The first way happens to be using an intake fan, and the other by using an exhaust system. The intake fan takes the air from the outside source. Simultaneously, the passive exhaust system draws in the fresh air by releasing the polluted one through an exhaust duct.

The outside source is normally a separate room in your house the hallway, basement, attic, basement, or a cracked window. The air derived directly from the outside can also be considered as one of the outside sources. However, for this filtering, the air for bugs and large particles is quite significant.

Both these sources have some positives and negatives attached. The open-loop systems constantly push and pull in the fresher and cleaner air into the growing area. However, using an exhaust system to put out the contaminated air is always better, and we prefer it for its benefits. The exhaust helps create a passive intake system, meaning it pulls in the fresh air into the grow room while pushing out the impure air. Putting it simply, a cracked door frame and a window an open port wall are some of the ways to provide fresh air into the grow area.

Choosing the Right Size for Your Room Ventilation System

When choosing the size of your room ventilation system, consider the formula: “Length x Width x Height/ 5”

The numerator provides us with the room's total area and dividing it by five means changing the room's air every five minutes. The number you obtain from the formula is the minimum cubic feet per minute, or CFM. This is the throughput performance of the ventilation system ' carbon filter or the fan you use.

If you haven't yet understood, consider this example below.


Length = 10

Width = 8

Height = 8

For the length by width and height multiplication, we get 640. When we divide 640 by five, the answer we get is 128. This is the amount the fan and the carbon filter need to handle when replacing the grow room's air. Precisely, 128 is the minimum CFM rating for the equipment you use as your grow room ventilation system.

Open Loop Grow Rooms and CO2

With your grow room constantly changing the air, using CO2 generators with an open-loop system is never a good idea. The reason is that the CO2 will be of no use as it will either dilute or be removed. This is also why most open-loop systems don't necessarily require a dehumidifier or an air conditioner. With air constantly changing, there's no chance of heat or humidity build-up. The open-loop systems don't normally have many components, which is one reason you get to save money on your electricity bill every month.

Grow Rooms (Closed Loop)

When it comes to using closed-loop systems, the system uses CO2 gas to supply fresh air inside the grow room. The closed-loop systems don't bank on the intake systems as an open-loop grow room does. With the exhaust inside the grow room, managed and controlled, it is only turned on when temperatures escalate unexpectedly. Or when the humidity levels rise up to a dangerous level.

For this very reason, most growers using a closed-loop consider turning their exhaust systems every ten to fifteen minutes. This helps them ensure that the air doesn't go dry with time. In contrast, after activating, the timed exhaust fan removes humidity, heat, and excess CO2, which the CO2 generator produces till its PPM levels touch the required level for growth.

Furthermore, usually, growers don't prefer adding more heat and humidity in their grow room as the grow lights and plants produce them on their own. However, the closed-loop systems need cool air to surpass the heat from the grow lights and to dehumidify the air inside the grow room. This is one of the reasons closed-loop systems require air conditioners.

Understanding CO2 and Why do we need it in Grow Rooms?

As obvious as it is, CO2 is already present in the air. With natural concentrations of about four hundred ppm, plants require CO2 to carry out photosynthesis. Putting it simply, plants use CO2 to produce energy.

During the process, plants use light to convert CO2 into energy. And this is exactly what makes the process simple and highly effective. It would then help if you grew lights with strong power to benefit from this carbon dioxide.

For this, be sure not to use fluorescent bulbs. These are neither as strong nor have enough wattage to let plants benefit from the CO2. Instead, use the one with higher wattage, MH/ HPS, LED, or LEC lights. These will ensure you take advantage of the CO2 enrichment from your grow room.

Controlling Temperature, CO2, and Humidity in the Grow Room

If you are growing indoors, you might start by creating an artificial environment. You probably have made sure that your environment provides your plants with everything they can need. Everything needs to be balanced from the nutrients to provide your plants with the right grow area to ensure your plant's overall growth. However, monitoring your grow room's humidity, temperature, and CO2 is another critical factor no grower should overlook.

The Temperature in the Grow Room

Temperature is another factor; you should never overlook when growing plants. It helps in the balanced growth of the plant by establishing a basis for its development.

Typically, plants in their initial stage demand higher temperatures. With higher temperatures, they get to absorb the moisture using the stomata present in leaves as the root system develops. However, it's better to turn the temperature down with time as the plants grow more and more.

Precisely put, the seedling in the plants prefer a daytime temperature around 68-77- or 62-72 degrees Fahrenheit as the lights go down. In contrast, senior plants can breathe in around 82 degrees Fahrenheit.

The location of the growing area happens to affect the grow area's temperature quite critically. What's a grow room without the right temperature? The ideal range for your plant growth varies depending on factors like size, type, and the number of lights used in addition to extraction rate as well airflow configuration.

Once the grow room's temperature adjusts, the risks of mold and mildew decrease. However, the fluctuation in the temperature shouldn't be too high. Otherwise, it can affect a plant's growth quite significantly. Be sure to keep the temperature around five degrees to 10 degrees Fahrenheit at max.

Controlling heat in the Grow Room

You can control the temperature in your grow room by using an analog or digital thermometer. You can consider putting these in several different places to measure the temperature but don't forget to check the temperature when there's shade in the grow room. In some thermometers, a memory is present that helps record the changing temperature in a grow room. In most cases, the crops are placed in different sections, creating different chambers of cooler and warmer temperatures as required.

When wanting to tune the temperature to a cooler setting, you can use LED lights. These lights can be used at night and during the daytime when the temperature is cool. You can also consider increasing the room's ventilation system if you want the temperature to settle down.

In contrast, using HID lights turn the temperature to a warmer setting. From using heating pads, and switches to additional lights, you can use different tools to make the grow room's temperature warmer. But then again, if you want a perfect tool to control your grow room's temperature, the air conditioner is incredible. With several portable and commercial A/C's available, these come in handy for indoor growing.

Don't forget to consider our guide to get more information on grow room ventilation.

Humidity in the Grow Room

Humidity and temperature go hand in hand, setting ideal growing conditions in the grow room. When understanding the quantity of moisture in the air at a certain temperature, relative humidity (RH) is the measure. This compares the quantity of moisture the air can hold at that particular temperature.

Consider the example, for instance:

RH of fifty percent at ninety-degree temperature depicts the air isn't completely filled with moisture. To put it simply, the hotter the temperature, the more its tendency to hold more quantity of moisture.

Similarly, crops require an ideal percentage of humidity to grow. With low humidity levels, plants consume nutrient solutions in more quantity than required. One of the reasons for this is that because of the low moisture in the leaf stomata, plants are unable to suck moisture from it. As a result, the nutrient salt increases, and the leaves wilt, having blistering edges. Furthermore, with humidity levels increasing higher, the chances of mold and mildew increase.

However, since plants demand a higher level of humidity during the growth period, growers should adjust the humidity levels as per the plant's requirements. Such plants have roots that are not fully developed, and humidity levels play a crucial role in a plant's development. You can adjust the humidity levels by decreasing them to five percent every week until it reaches forty percent.

With time, as you become an advanced grower, you can manipulate VPD typically known as vapor pressure deficit. In this way, you'll provide your plants with an ideal growing environment all through the plant's life leading you to get healthier yields.

Controlling Humidity in the Grow Room

One way to control humidity levels in the plant is by watering them when the grow lights are on. This helps the plants evaporate humidity better. You can also consider shaking excess water from the plants to protect them from getting molds and insecticides as the plants bloom.

Another hack for the grow room to have the right humidity levels is by using ventilation systems. The hygrometer is an excellent way to measure temperature. With several existing devices, you can use any device to measure the humidity levels, and temperature in a grow room. There are different instruments and tools you can use to record humidity levels and store data accordingly.

When considering increasing humidity levels, you can turn on the lighting in your grow room. You can further try to decrease the ventilation system to a bare minimum. If not, you can also try misting the humidifier to increase the moisture in the air. And in case to decrease the moisture level in the air, you can use hydroponic-grade dehumidifiers and fans. Precisely, the poorer the ventilation system in your grow room, the more watered plants you get.

The idea is that every time plants exhale, they liberate excess water. The poor ventilation system does not suck up the moisture in the air, and the plants get soggy and tend to mold easily.

CO2 in the Grow Room

Just as different elements, compounds, and nutrients add to a plant's growth, carbon dioxide is significant to plant growth. Two of the major sources of carbon dioxide are plants' and animals' respiration. You get carbon dioxide as a by-product of their respiration.

The grow area uses carbon dioxide during the process of photosynthesis. The ambient air escalates the plant's growth, and the absence of it can put the plant's growth to quite a halt. When it comes to the growth stage or simply the first few weeks, CO2 adds significantly to the plant's growth.

The Relationship between Grow Lights and CO2

Different lights are available, which can easily be taken as one of the sources of carbon dioxide. For example, fluorescents and CFLs already have carbon dioxide available in larger quantities. This is why adding more carbon dioxide in the presence of CFLs or fluorescents can be insignificant.

But when using LED or MH/HPS grow lights, supplying CO2 to the grow area can help increase your overall yield. In other words, in the rooms filled with intense grow lights, the addition of CO2 increases photosynthesis. The reason is that plants use intense lights to elevate the process of photosynthesis. They use this light to create more energy, increase growth, and yield more at a quicker pace.

Carbon dioxide tends to make these plants heat and light-resistant. Further, it is advisable to use carbon dioxide in grow rooms, keeping the temperature at eighty to ninety Fahrenheit. This temperature paves the way for the plants to lose excess water from within them. This particular process is called transpiration.

CO2 in the Grow Room

For a small amount of carbon dioxide in a grow room, you don't need to seal the room. Even without sealing the growing area, you can get your desired concentration in the range of 1200-1500 ppm. Precisely, a closed loop is not critical when adding a smaller portion of CO2 is in question. Some of the tools you can choose to add CO2 to your growing area are CO2 generators and CO2 compressors. These have timers inbuilt that you can use to set up generators or a CO2 tank for a specified amount of time.

Several CO2 monitors can be used to measure CO2 in the growing area. With these monitors, you can turn on the regulators whenever CO2 levels drop below the already set amount. These monitors also have photocells that ensure CO2 doesn't distribute at night.

Other than that, distributing CO2 through the growing area is not difficult. Since CO2 is more in weightage than air, turning on fans easily distribute it through the grow room. However, in the nighttime, don't forget to switch off CO2, as at night, plants stop their photosynthesis process.

You can learn about using CO2 in the grow room and calculating it by checking out our guide.

Controlling the Odors in the Grow Room

You can easily control odors in a growing area. Just use the right tools and techniques to ensure it stays unharmed throughout the process. You can consider exhaust systems or intake holes to liberate the odors from the grow room. One of the strategies can be to check for the ports in the grow room to know where the fresh air comes and leaves from. Knowing this is quite mandatory as it helps you efficiently control odors inside the grow room.

In most cases, grow rooms have carbon filters connected to an inline fan. These fans help to scrub the odors away by pulling the air using its activated carbon filter. Then it exhales the air out of the room. Even then, there will be times when releasing odors especially hot and smelly might not be possible. In such cases, you can consider ozone generators, negative ion generators, and fragrant gels to fight the smells in your grow room.

For further information, you can consider our guide on managing grow room odors. Additionally, here's a quick overview of different techniques and products you can consider to control your grow area's odors.

Carbon Filters (Activated)

Activated carbon helps with controlling the odors inside the grow room. As oxygen activates carbon filters and opens pores on the carbon, the open pores in the carbon soak the odor molecules and particles present in the air.

Carbon filters have CFM ratings. CFM stands for cubic foot per minute ratings. With CFM ratings, you get to find the amount of air passing through the filters and clean the air's contaminants. However, you want to ensure you don't run air through the carbon filters to overload the carbon. Overloading the carbon can result in smells in the grow room, making the filters ineffective.

In contrast, the carbon filter size is also playing a role in controlling the odors in your grow room. The lesser the air passes through the filter, the bigger (more than required) the filter's size. In most cases, carbon filters last for a year or two, depending on the environment you keep them in. The more humidity you expose them with, the lesser their life span gets. For example, grow rooms having humidity levels above seventy percent can trigger their life span to quite an extent. In short, it decreases by half as much. Once the carbon filters are empty, you'd either have to refill them or replace them completely.

The Size of the Carbon Filter

Installing carbon filters in any grow tent or a grow room is no big task. The filters come in flange sizes ' you can easily bend them and in different size ranges. The size normally ranges from four inches to twelve inches in diameter. The length of the ducts is, however, almost sixty inches normally.

Considering you need to change the air in your grow area every five minutes, the size of the carbon filter matters the most. The filters should be capable of moving around thirty to sixty cubic feet every minute. The flow of the air is also quite critical, and the size of the carbon filters impacts the airflow significantly. That said, don't forget to remove the vacuum from your grow space ensure the fresher comes in and the impure one leaves as fast as possible. For this, it is advisable to pull air with the filter and push it out from the grow tent.

Normally you'd see filters hanging from the ceiling of the grow space. This allows the filters to cover plants in all the nooks and crannies of the grow space. Furthermore, it helps liberate the warmer air coming from the top of the grow space. Then again, to hang them from the ceilings, you need to ensure the carbon filters are just about the right size. Otherwise, you'll have to place them on the ground without getting your desired results.

Here are the ways carbon filters are set up, normally in a grow space.

  • Recirculating Carbon Filter Setup
  • Exhaust Fan on the timer
  • Constantly Running Exhaust Fan

Ion Generators (Negative)

It is quite likely that you don't see negative ion generators in today's grow room. These are not common; however, they help a great deal in neutralizing the smell. That is, these devices give rise to ions (negatively charged) the negative ions combine with the positive odor and the contaminated ones. This is how the Ion generators neutralize the smell in the air.

Generators (Ozone)

The generator is by far quite the uncommon method to control the smells in the air. The idea behind an ozone generator is that it converts the oxygen in the air into pure, fresh, and healthy O2. It does it by exposing the impure air to ultraviolet lights.

You can keep Ozone generators inside the grow room or inline them with the exhaust ducting. Here are some of the finest generators available because you don't need to replace them after a certain period. But you don't want to inhale the air coming from ozone generators as it is harmful to the human lungs.

Odor Absorbing Gel Sprays

Odor absorbing Gel Sprays can be ideal for fighting the odors in your grow area. However, these don't remove or neutralize the air instead, they mask the smell in the grow room. Chances are, using these might not work as effectively as others in the list if you're growing in a large growing area.

Precisely, before choosing any of the methods, tools, or techniques when combating the smells in your growing area, don't forget to consider these tips to make things easier for you.


At, you would find grow room controllers to automate different aspects of your grow room something that'll make growing quite simple for you. As a result, these can also become a necessity for you too.

Confused, if you may, on how to use controllers, you can consider our guide on grow room setup to get tips on making your job easier.

Sep 20th 2022
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