Cannabis facilities: air filtration,
UV-C air disinfection and odor removal

NAFA interviews Keith Jordan, May 2020

Cannabis legalization has been a passionate topic over the last few years and is engulfing many countries and states. In the beginning of the legalization movement, many Cannabis growers were only concerned with a few items such as plant nutrients, pH water balance or the type of halogen grow lights recommended. Very little, if any, thought was imparted to indoor air quality. Slowly, over the last 5 years, Cannabis growers are realizing that Indoor air quality provides as much value as any other technique in the growing process. Growers understand there are a large number of contaminants that can damage and wipe out an entire crop, thus learning about proper indoor air quality is quickly gaining prominence.

Cannabis growers operate in three methods – outdoor grow similar to a farm, greenhouse similar to vegetables, and fully enclosed warehouse with Heating, Ventilation, and Air Conditioning system (HVAC). Outdoor growers harvest once a year, greenhouse growers harvest roughly 4 times a year and warehouse growers harvest 6-8 times a year. The top of the line, best quality and quickest harvests occur with a warehouse grower. NAFA members can engage the role of educating the grower on the best and most efficient method of removing particulates, disinfecting molds, fungus, bacteria, and mitigating pungent cannabis odors.



The warehouse grower has anywhere from 100 to 10,000 plants inside a large room or multiple rooms which are full of dirt pots, 1000 watt growing lamps creating a massive heat load, circular fans on the walls stirring up dust, and high numbers of air changes per hour through the HVAC system. Operating indoors with the above opposing systems can rapidly increase the particulate load to that of dust storm. These opposing forces will continually increase the level of particulates as well as circulate those particulates around the room, through the HVAC system spreading contamination and dust virtually on every surface of the room. The current level of filtration for the majority of warehouse growers consists of a 1” MERV 8 pleated filter. Several reasons for this stem from utilizing 5 ton HVAC systems, choosing the cheapest filters, or a recommendation from an HVAC contractor.

The warehouse grower that has retrofitted a warehouse typically has multiple 5 ton AHU per room. The new facility built from the ground up typically has 15 to 25 ton AHU. Most growers are so concerned with overcoming the heat load of their grow lights and reducing humidification levels, that they are hesitant to increase filtration because of pressure drop. The HVAC contractor sizes the system to provide the grower with anywhere from 10 to 18 air changes per hour and does not educate the grower on the vast array of filtration efficiencies or sizes, thus why 1” MERV 8 pleats are the most common with Cannabis growers currently. This is a perfect situation where NAFA members can be of crucial benefit to growers in educating them that a higher efficiency filter will not necessarily affect the heating/cooling loads when sized properly and can lower life cycle costs of the filter as well as the AHU.


UV-C air disinfection

The warehouse Cannabis grower is especially susceptible to the infection of Powdery Mildew and Botrytis which infiltrate the facility and continually infect the Cannabis buds causing a stunting of growth, distortion of quality, a reduction of terpenes and degraded product that must be discarded or used for oil extraction.

Commercial UV-C Air disinfection systems are being utilized with success in preventing the outbreak and spread of Powdery Mildew and Botrytis as well as assisting in the grower consistently passing the state mold CFU tests required at each harvest. The UV-C system is sized based on cubic feet per minute (CFM) of the HVAC system, return or supply duct dimensions, cubic feet of the room to be disinfected and the number of air changes achieved on an hourly basis. An effective UV-C system should be designed to achieve an average of 95% hourly disinfection of Powdery Mildew utilizing a recirculation rate of 8 air changes per hour. This ensures that all the air in the room will be processed through the UV-C air disinfection system multiple times.

Currently, the most efficient and economical approach is to utilize the HVAC system as a point of disinfection. As mentioned above, most growers are attaining on average 10-18 air changes per hour. By installing a commercial UV-C Air Disinfection system in the return or supply HVAC ductwork the air can be disinfected at a high level due to the high air exchange rate. Stand alone or portable UV-C systems can be utilized if they are sized to achieve 8 or more air changes per hour with high intensity UV-C air disinfection lamps. UV-C air disinfection is a complimentary system to filtration necessary to provide a synergistic punch to quickly reduce mold, bacteria and virus contaminants within the warehouse grower.

Odor removal

The growing of Cannabis produces a pungent and dense odor. Many think of a skunk when they smell the Cannabis odors. Inside the growing facility, the odor is accepted and anticipated. However; outside near neighborhoods and offices, many find the odor to be offensive and bothersome. In fact, many cities are issuing regulations regarding odor control and enacting fines when odors are smelled and reported outside of the facility. This poses another costly issue for the warehouse grower when maintaining negative pressure. Depending on the regulations, growers choose between a closed loop/non-exhaust system or a negative pressure system, very few if any have positive pressure set ups. The main reason is to keep C02 and odors inside the facility. Though, for the grower who actively exhausts indoor air, odor removal is mandatory, cumbersome and difficult.

Currently, can or tube carbon filters are most commonly used for the mitigation of the Cannabis odors. The majority of these filters are purchased through Cannabis growing supply stores (similar to garden stores). Due to the potency of the odor, removal of this odor requires a constant supply of can/tube filters or a commercial carbon filter set up. The commercial set up contains bulk fill carbon housings on the exhaust air which greatly increase the elimination of the cannabis odors being exhausted.
Lastly, it is important to understand these odor regulations are not consistent from state to state nor are always very clear. It is important when working with these facilities that you understand the regulations that have been imposed on this market.


As Cannabis legalization continues to progress throughout the world, it is extremely beneficial to NAFA members to reach out and educate Cannabis growers on proper indoor air quality. Filtration, UV-C air disinfection, and odor mitigation will always be important topics for the Cannabis grower as they directly impact the growing space. NAFA is positioned as a leader and should enact recommendations and guidelines for indoor air quality within Cannabis industry. Currently, there are no other organizations with the expertise of NAFA members poised to assist this progressive and expanding industry.

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