The Symbiotic Relationship Between CO2 and Ventilation

By Matt LeBannister
Published: December 1, 2016 | Last updated: April 21, 2021 11:38:54
Key Takeaways

Gardening indoors allows gardeners can control every aspect of the environment in order to propel the production of their plants beyond the norm. However, since everything in the growroom is interconnected, it can spell disaster if one aspect gets out of whack.

Caption: Electric ventilators in greenhouse Source: ntdanai/Shutterstock

The indoor garden is a chain of networks much like the human body. If one element of that system fails or is not working at the required level, then the whole chain becomes weakened and the system can collapse. You can have as many high-quality HID light bulbs running in a room, but if the nutrient levels are too low, it will make no difference.


You can use the best nutrients that money can buy, but you will just be flushing money down the drain if the pH levels are not in the ideal 5.8 to 6.5 range. The same applies to CO2-enrichment systems—if you are not ventilating the room, expelling stale air, bringing in fresh air and keeping the temperature and CO2 at a plant friendly level, you might actually be doing your plants more harm than good.

Read also: Perfecting the pH of Your Hydroponic Nutrient Solution


This article aims to highlight and tackle the symbiotic relationship between CO2 generators and ventilation, and how they cannot truly benefit your plants in the desired way without working together in harmony.

What Can CO2 Do For Your Garden?

CO2 is used by plants in photosynthesis, the process through which the plant converts energy from the sun, water and CO2 into sugars and O2. The air around us contains roughly 200 to 300 ppm (or, 0.02 to 0.03%) CO2.

Plants do well in this range, but we have learned that you can supercharge your garden by enriching the atmosphere in your grow room to 1,200 to 1,500 ppm (or, 0.12 to 0.15%)—however, keep in mind that anything above this can be harmful to plants and humans. When every aspect of the garden system is aligned, this CO2 enrichment has been known to double, even triple, yields.


CO2 enrichment also allows stems and branches to grow faster, often causing tremendous growth in plants during the vegetative stage. This can actually take weeks off the amount of time you would need to grow your plants before they were large enough to switch to the flowering stage. This saves you time, as well as money.

Read also: How to Gain Control of Your Gardens pH, ppm, and EC Levels


You can also get more crop rotations in each year, saving you money on electricity. If you are using HID bulbs in your garden, the number of lumens and PAR watts drops off over time; however, CO2 enrichment allows you to efficiently utilize the bulbs in your growroom and get the most out of them. You might get one more crop rotation per bulb when adding CO2 to your garden then without, and that’s just money back in your pocket.

Another benefit of enriching your growing atmosphere with CO2 is that plants in this environment can handle growing at higher temperatures. In fact, they prefer it. The ideal temperature for plants in a CO2 enriched environment is roughly 85ºF. (Keep in mind, however, that fluorescent light bulbs should not be used if you’re CO2-enriching the atmosphere of your growroom.

Fast growing plants require intense light to produce large yields and CO2 enrichment will only enhance the plant’s ability to absorb and assimilate PAR. With the temperature in the room higher, metabolic rates within the plant will accelerate and growth will increase. This also means that you can run ventilation fans less. In summer months, you won’t need to run your air conditioning as high or as frequently. This can mean some big savings on your electricity bill.

Read also: CO2 Enrichment Acclimation and Efficiency in Hydroponic Growing

Generating CO2 For Your Garden

There are many ways of generating CO2. Some ways are easier and more reliable than others but each can be effective.

Fermentation and decomposition, like the processes used to make wine or organic compost, can be utilized to produce CO2. However, one issue with these methods is that it’s impossible to control that amount of CO2 being made—it can vary depending on certain factors, such as room temperature.

Also, there is the problem of the potential odors produced by having organics decomposing in your growroom. These would attract pests.

Using dry ice is another way to enrich your growroom’s atmosphere with CO2. Dry ice is frozen CO2 that turns from a solid to gas when it comes into contact with the atmosphere, without ever becoming a liquid.

The downside to using dry ice is that it is difficult to store enough of it to replenish larger growrooms. Dry ice is only practical in the smallest growrooms, and even then it can be expensive.

Read also: CO2 Supplementation Simplified

A CO2 emitter is a practical and cost-effective way of enriching a small, single-light room with CO2. A CO2 emitter system uses tanks of compressed CO2 and pumps it through tubing throughout your room using regulators and valves.

Since CO2 is heavier than air, it is most effective when the tubing is placed along the ceiling of your room above the plants. This will allow the CO2 to fall amongst the foliage where it can be used by the plants. Also, CO2 emitter tanks can be refilled at most hydroponics retailers at an affordable cost.

CO2 Climate Control in a greenhouseCO2 tanks for climate control in a greenhouse. Source: Toonix/Shutterstock

CO2 generator systems are the most practical for larger scale or commercial growrooms with multiple lights. This system involves creating CO2 by burning fossil fuels, usually natural gas or liquid propane (other fuels might not be safe and can emit poisonous gas as a byproduct).

The downside to using CO2 generators is that they have a pilot light burning at all times, which can be a risk. There is also heat given off as a byproduct and in rooms with multiple lights, extra heat can be an issue.

There are so many other ways to generate CO2 in your growroom. Some people use a butane lamp to add the extra CO2. There are also a number of products available at hydroponics retailers.

Some create CO2 as a chemical byproduct, and there are many that are a variation or a combination of the systems mentioned above. Or, there is always the old-fashioned technique of sitting in your growroom and talking to your plants for a few hours a day.

Read also: Ventilation Systems for Greenhouses and Indoor Gardens

Regulation, Ventilation, and Circulation of CO2

There are number of reasons we need to ventilate our growrooms. If the temperature becomes too high, we need to remove the heat from the room. When there is an excess of humidity, it must be vented from the growroom to prevent things like powdery mildew from inflicting our plants.

Ventilation is also needed when CO2 levels are toxic or too low. When enriching the atmosphere of your growroom with CO2, the trick is to manage all these things while keeping the CO2 in the air long enough for it to be of some benefit to your plants.

With CO2 being heavier than air, you must also consider circulating it throughout the growroom. A couple well-placed oscillating fans positioned near where the CO2 is being released can do a fantastic job of circulating the CO2 and keeping it off of the floor.

As mentioned above, there really is no way of regulation how much CO2 is being produced when generating CO2 via fermentation, decomposition or dry ice. You only have control of how much is allowed to stay in the room.

There are some very high-tech devices that can be used to measure CO2 levels. You can hook you fans up to a CO2 monitor specifically designed for growing and have it set to vent your room once the CO2 levels reach a stage that could be harmful for plants or humans.

Alternatively, you can set up the exhaust fans to a thermostat that will vent your growroom once the room reaches a certain temperature deemed to be too high for the plants to thrive.

If you are using a CO2 generator or CO2 emitter system, you can have more control. There are some great interfacing products that can totally monitor and control the levels of CO2 being generated in the room, as well as monitoring the humidity and room temperature.

They can shut off fans when CO2 is being generated, shut off CO2 generators when they hit the ideal level and then turn on fans when the room becomes excessively humid or too hot for the plants. These products can be expensive, but they offer the gardener total control of these elements and you really can’t put a price tag on that.

Garden systems are only as strong as their weakest link. CO2-enrichment is no different. If you are not using your exhaust fans properly, providing the right types and levels of nutrients, using the right spectrum and strength of lights, you will be wasting your time by enriching your growroom atmosphere with CO2.

However, having all these factors dialed in and enriching your grow space with CO2 can lead to tremendous growth and yields. When gardening with CO2, the sky’s the limit.

Sources: Gardening Indoors, The Indoor Gardening Bible by George Van Patten

Read next: Plant Growth and the Light Spectrum


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Written by Matt LeBannister

Profile Picture of Matt LeBannister
Matt LeBannister developed a green thumb as a child, having been born into a family of experienced gardeners. During his career, he has managed a hydroponic retail store and represented leading companies at the Indoor Gardening Expos. Matt has been writing articles for Maximum Yield since 2007. His articles are published around the world.

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