Filters, Ozone Generators and Air Purifiers, Oh My!

By Eric Hopper
Published: September 1, 2015 | Last updated: April 21, 2021 05:47:34
Key Takeaways

Whether it is implementing filters, ozone generators, air purification devices or a combination of solutions, indoor growers need to do what they can to ensure their gardens are protected from uninvited pathogens. Filtering or purifying the air automatically reduces the development of molds that could quickly destroy an otherwise healthy crop. Here’s a rundown of the various solutions available to growers.

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Ventilation is one of the most important aspects of a properly operating indoor garden. The ventilation system should provide the grower with ultimate control over temperature, humidity, CO2 concentration and air quality. The latter—air quality—is an aspect of the ventilation system that many growers overlook entirely. However, air quality is becoming more and more important.


This is especially true when crops are subjected to tests for residual molds and chemicals. Indoor gardeners wanting to grow the highest-quality crops will need to implement filters or other air purification devices to maintain a high quality of air in their growroom.

Best Air Filters for Growrooms

Probably the most commonly used devices that affect air quality in an indoor garden are filters. Both intake and exhaust filters, as well as stand-alone circulation filtration systems, are regularly used in indoor gardens.


Intake Filters – Intake filters are designed to filter the air coming into the garden space. Often, these filters are placed on the garden’s intake fans. The filter can be placed within or outside of the garden as long as the flow of air travels through the filter before entering the garden space. Intake filters are great preventive tools. These filters will catch a good amount of dust, debris, insects and mold spores, ensuring less problems in the long run.

The construction of intake filters can vary greatly, but they are all designed to maximize air flow while filtering as much as possible. High Efficiency Particulate Air (HEPA) filters are common, as they are able to remove particles in the air down to .3 microns in size. Many mold spores fall in the 1-20-micron size, which means HEPA filters are a good choice for preventive protection against molds.

Although some HEPA filters include an antimicrobial coating, HEPA filters can trap a large amount of viable spores, so removing a used HEPA filter without special care could potentially spread mold spores all over the garden. If possible, bag the filter when taking it down for cleaning, and remove it entirely from the garden space before cleaning, which reduces the likelihood of accidental contamination.


Indoor gardens with air-cooled reflectors can benefit from intake filters on the intake portion of the air-cooled system. Even in closed, air-cooled systems, intake filters can help a garden’s performance immensely. Dirt and dust settled on a reflector’s glass can greatly reduce the efficiency of a lighting system by blocking some of the light that would otherwise reach the plant canopy. By filtering the air before it enters the air-cooling system, a grower can greatly reduce sediment buildup on reflectors, and keep the light levels as high as possible.

Exhaust Filters – Exhaust filters are connected to the exhaust portion of the ventilation system and are designed to filter the air as it leaves the garden space. Exhaust filters can effectively filter VOCs (volatile organic compounds), including odors from fertilizers, pesticides or other particulates that may need to be contained within the garden space.


Most exhaust filters used by indoor gardeners are carbon filters. Carbon filters are great at filtering VOCs, which is why they are so popular for indoor growers. The exhaust system should be set up to draw through the filter and then out of the garden space. This ensures the air is filtered before exiting the garden.

Generally speaking, the exhaust of a ventilation system should be set in the upper portion of the room, where it will be able to do its job more efficiently, as heat naturally rises. Unfortunately, carbon filters are heavy pieces of equipment and placing them close to the ceiling is not always an easy task.

Hanging chains from the ceiling, attached to the building’s studs, is a great way to secure a heavy carbon filter. For growrooms where hanging a filter is not an option, gardeners can purchase an adjustable carbon filter stand from an indoor gardening shop.

Stand-alone Filters – Stand-alone filters are filters combined with a fan that are set up within the growroom. The purpose of a stand-alone filter is to recirculate the air within the garden space and filter it in the process. Stand-alone filter systems do not filter the air as it enters or exits the garden; they continuously filter the air within the garden. This is a great way to reduce or eliminate odors and can also work to help reduce the likelihood of mold problems.

After being accidentally introduced into a garden, mold spores can be caught by the circulating filter before settling on plants. A stand-alone filter, combined with intake and exhaust filters, is a great way to prevent problems and eliminate odors.

Ozone Generators

Another device used by gardeners for air purification is an ozone generator. An ozone generator does exactly what its name implies: generates ozone. Ozone (O3) is a powerful oxidizer that will oxidize any molds, bacteria or odors it comes in contact with. The problem with ozone is that it is not at all selective. In other words, it doesn’t necessarily pick and choose what it oxidizes.

For safety’s sake, indoor growers should only use ozone generators on the exhaust portion of the ventilation system. High concentrations of ozone can be harmful for people and plants, making these devices less than desirable for use within the growroom. Even at levels below the danger threshold for humans, ozone can oxidize essential oils produced by plants, which causes the plants to lose vitality and quality. This is why ozone generators should only be used to purify the air as it is exhausted from the garden space.

Air Purifiers

More and more growers are using air purifiers in their growrooms in addition to the intake and exhaust filters. The main purpose of an air purifier is to eliminate any mold spores or bacteria missed by the filters before they can affect the plants within the garden. An air purifier can be a great addition to any indoor garden.

However, not all air purifiers work the same. Many air purifiers are simply HEPA filters paired with a low-powered fan. These types of air purifiers would be of little use to a gardener with a decent-sized garden. A gardener considering one of these filters would probably be better off opting for an inline fan and HEPA filter combo.

Some of the other air purifiers on the market are nothing more than hyped-up ozone generators. These filters should be avoided because they may produce too much ozone, which would cause the same problems as operating an ozone generator.

The best type of air purification device for indoor gardeners is a photocatalytic air purification system. These air purifiers are not cheap, but they will remove molds before they become an issue. Photocatalytic air purifiers use specialized catalysts that, with the help of some UV light, create powerful oxidizers.

As the air is circulated through the air purifier, the oxidizers destroy offending intruders. The devices that produce no detectable ozone are the best bet as they can be used safely in the garden space and are especially useful for growers who are looking to produce consistent, mold-free crops time after time.

Purchasing a photocatalytic air purifier is a lot like purchasing an insurance policy. Growers may never actually need it, but if they do, it could save their gardens. As the cost of photocatalytic air purification systems goes down, I believe more people will put them in their growrooms as a precautionary measure.

Bottom Line

Many indoor growers take precautions to ensure they have clean water and soil, but too many overlook the need for clean air. In most cases, purified air does not affect plant growth as much as clean water and soil, but it still plays an important role in the quality of the finished crop.

In the future, I believe we will see more growers paying closer attention to air quality. Pure air in the garden will become essential, as the testing of a crop’s purity becomes more mainstream.

Crops with residual molds or VOCs will no longer be acceptable, and growers who want to ensure they have clean crops will have to take steps to purify the air in their growrooms. If anything, air purification should be included as a precautionary measure. As the old saying goes, an ounce of prevention is worth a pound of cure.


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Written by Eric Hopper | Writer, Consultant, Product Tester

Profile Picture of Eric Hopper

Eric Hopper’s past experiences within the indoor gardening industry include being a hydroponic retail store manager and owner. Currently, he works as a writer, consultant and product tester for various indoor horticulture companies. His inquisitive nature keeps him busy seeking new technologies and methods that could help maximize a garden’s performance.

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