The grow room can be an endless source of odors. Reservoirs, nutrient solutions, fertilizers and organic amendments such as guano off-gassing from pots -- and even some types of plants -- can give off odors that are either unpleasant or unwanted outside of the grow room.
But just because an indoor garden is constantly producing odors doesn't mean those smells can't be controlled.
The two most popular ways of removing odors from the grow room air are carbon filters and ozone generators.
A filtration system normally includes a carbon filter, a fan, and (in the case of most carbon filters) a flange to connect the fan to the filter. Because the filters and the flanges are not always from the same manufacturer, compatibility issues often occur, although some filters, such as the Can Lite series, have a built-in flange.
A carbon filter is usually a cylindrical unit that looks like a muffler on a big-rig truck. A flange connects to the top so an exhaust fan or ducting can be attached. The exhaust fan either pushes air into or pulls air through the filter and across a bed of carbon inside the filter.
Fans tend to work more efficiently when they are pushing air, so most growers prefer to mount the fan on top of the filter so it is pulling grow room air through the filter and pushing the cleansed air through the exhaust system. Not only does this cause a little less strain on the fan, but the positive pressure inside the exhaust system keeps untreated grow room odor and CO2 from being sucked into leaks in ducting and exhausted.
The carbon in the filter absorbs the odors and other organic compounds. Carbon filtration is the only method that actually eliminates odor and does not produce any potentially harmful side effects or byproducts. The most common materials for carbon filters are mined carbons or coco carbon, which is made from coconut husks.
Temperature and humidity are the factors that primarily affect the efficiency and performance of carbon filters. As either increases, the efficiency and the odor removal capabilities drop. As temperatures get into the 90s, performance really starts to suffer. Humidity around 10 percent is best. However, most grow rooms are going to have at least 30 percent to 50 percent humidity, which is fine. But as humidity increases to 70 percent or 90 percent, the tiny pores in the carbon start to fill up with moisture, making the filter ineffective.
For the carbon to work properly, air needs to pass through it at a certain rate. If the air passes too quickly, there is not enough contact time and the chemical reaction that neutralizes the odor isn’t complete. If the air flows too slowly, odor control becomes inefficient. But with temperature and humidity within range, and with a properly matched fan and filter combination, growers can achieve sufficient odor control.
Growers must combine the correct size of filter and fan to ensure air flows through the carbon at the right rate. To find the right match, first calculate the size of the grow room in cubic feet (LxWxH). To bring in fresh air and adequately filter the exhaust, air in the grow room should pass through the filter every one to four minutes, with one- to two-minute exchange times being optimal. So that means in a 1,000-cubic-foot grow room (about 10' x 12' x 8'), 250 to 1,000 cubic feet of air should pass through the filter each minute.
However, an appropriately sized carbon filter reduces a fan’s CFM rating by about 20 percent. So, to changeover the air in a 1,000-cubic-foot room within the correct time frame, the grower would need a centrifugal fan with at least a 310 CFM, such as the 6” Max Fan, 6" Can Fan HO or 6" Vortex to achieve a roughly 4-minute exchange, or an 8” centrifugal fan with around 700 CFM to exchange the air in about 2 minutes. A 12” fan with roughly 1200 CFM will clear the room in about one minute.
With that calculation in hand, it is easy to match a fan with the appropriate size filter. Can Filters provides data on suitable CFM rating for their filters, giving ratings on the CFM required to remove odors from exhaust or for scrubbing the air in a sealed grow room. Can Filters also offers lab-tested data on the CFM their Can Fans will produce when paired with their filters, which can be used to help choose the right size fan. BetterGrow Hydro posts those ratings along with Can Filter listings on our Web site.
Some of the larger carbon filters can be too heavy to easily hang above the canopy in a grow room, where heat collects. The Can-Lite line of carbon filters feature thinner carbon beds, mainly for grow rooms where a lighter-weight carbon filter is necessary for installation. The thin carbon layer allows much more CFM to pass through, so if you have a 1000-CFM fan you might be getting 900 CFM passing through, instead of the 800 CFM a standard filter would produce. But, because there is less carbon in the filter, it does not eliminate as much odor in a single pass, so the air may have to pass through multiple times to do the same job from one pass in a thicker bed. These filters are rated for only 12 months at 100 percent efficiency, as opposed to 12 to 18 months for standard models. They are recommended for smaller grow rooms or rooms where installation limitations require a lighter weight filter.
The next consideration is how to place the odor filtration system in the room. If the room is sealed, and the grower is running supplemental CO2 and an air conditioner, then the carbon filter can simply be placed somewhere in the room and used as a scrubber so that the CO2 is not vented from the room. Ideally, the filter would be in a centralized location. If it is a larger room, multiple filters might be needed. They should be placed equal distances apart, right on the floor, standing vertically, so the flanges face the ceiling. They can also be hung from the ceiling, but in either case, you should try to maintain a buffer from the walls or ceilings of at least 12” to allow for unimpeded air flow through the filter. The fan can be put right into the flange of the carbon filter, and attached so that it becomes one continuous piece with some metal duct tape or a heavy-duty duct clamp with a neoprene collar to form a seal.
If the fan is hung from the ceiling, it must be anchored properly into the ceiling with hangers that will support its weight, such as the Heavy Duty 1/4” Rope Ratchet. Two of these used together will hold up to 300 pounds. Exhaust fans normally come with their own mounting bracket. Run a short length of duct from the fan to the filter and then another piece from the fan to the exhaust port in the room.
Can Filters come wrapped in a white prefilter that protects the carbon inside from dust and debris. To maintain unrestricted airflow, it is a good idea to change the prefilter at least every six months. To find a replacement prefilter for your Can Filter, click here.
The oxygen that is in air is a molecule that consists of two oxygen atoms. Ozone is oxygen with an extra atom. It is designated as O3. When ozone is released into the air, it seeks out anything organic and has an odor-neutralizing reaction in which it gives up one of its atoms to combine with the organic compound. The leftover double-oxygen molecule is simply released back into the air as breathable oxygen.
With ozone, something is being added to the air instead of being taken out (as with a carbon filter), yet it is still a clean and effective way to deodorize air.
Ozone has some drawbacks. It’s not ideal for plants or for people. It can also be detrimental to anything that can be oxidized, such as rubber and some metals. It is difficult to measure ozone or portion it properly, but a cycle timer, standard timer and a simple smell test can determine whether the right amount of ozone is being produced.
Ozone has a distinctive odor, slightly metallic. A person who is sensitive to ozone might experience a sore throat, or irritation in the nostrils as the ozone is actually oxidizing the mucus membranes. Short-term exposure is not generally a problem, but over the long term or in large quantities it can cause respiratory damage and also damage to the plants. It can also have an effect on the fragrance of flowers and herbs if too much ozone is present. If the ozone isn’t strong enough to smell, it’s probably not strong enough to deodorize.
Ozone has a half-life of only 15 to 20 minutes, so if the generator is turned off, within 15 minutes it’s gone from the air. That’s why BGH recommends ozone generators be used as part of an exhaust system. That way the ozone can be bumped up to a point where it is definitely oxidizing any odor molecules. And once ozone exits the room and hits the atmosphere outside, it quickly dissipates.
An ultraviolet ozone generator is commonly available in two forms. One is a standalone device that just sits in the room and discharges ozone. The other is shaped like a piece of ducting, so ducting or a fan can be attached to it and thus be used as part of the exhaust system, such as Blue Air’s line of Big Blue ozonators. Inside the generator are from one to five UV-producing lamps. Just as with carbon filters, it is important to run air through the ozone generator at a certain speed, otherwise there will be insufficient ozone added to the air, and insufficient deodorization. A mixing chamber where exhaust collects before being released into the atmosphere, or loops and bends in ducting, can help ensure the exhaust air blends with the ozone long enough to neutralize odors.
The amount of ozone that is generated depends on the size of the lamps, which come in 1’ to 1.5’ lengths. It might take several lamps to create the desired amount of ozone.
For some growers, the quality of the air entering the garden can be as important as removing odor from the air leaving the garden. For those who wants to keep their intake fan from bringing mites, dust, mold and other contaminants into the grow room, the Dust Shroom by Horti-Control is an effective way to do so.
The washable, reusable Dust Shroom (available in 4”, 6”, 8”, 10” and 12” models) causes virtually no back pressure. It is a foam filter coated with particle-trapping oil that attaches to the incoming air duct, and keeps dust, bugs, mold and bacteria out of the room.
Chemical Odor Neutralizers
Chemical odor neutralizers are usually either gels or liquids, or occasionally a solid waxy 'cake' infused with an odor-killing liquid. As the carrier dehydrates it releases a chemical deodorizing compound.
The gels, such as Ona Gel Pro, consist of absorbent granules that are saturated with deodorizing chemicals. With some brands, like Odor Killer Gel, the dried granules can be re-saturated with a liquid concentrate and reused.
There are a number of ways to tackle grow room odors for gardens large and small. So get over to BGHydro.com and get the funk out. If you have any questions about setting up your odor control system or adapting one to your particular needs and growing environment, give our techs a call at (877) 640-4769.