Grow room: The pros and cons of positive vs negative air pressure

Added on 08 September 2022

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Grow room: The pros and cons of positive vs negative air pressure

When faced with challenges of contamination and odor control, some indoor growers have adopted pressurized ventilation methods, manipulating positive and negative pressure to protect their grow spaces.

Pressurized rooms are often designed for use in clinical settings as they can be helpful in quarantining infected or immunocompromised patients. When faced with challenges of contamination and odor control, some indoor growers have adopted similar pressurized ventilation methods, manipulating positive and negative pressure to protect their grow spaces.

Key Differences Between Negative Pressure vs. Positive Pressure

Have you ever felt a rush of air or the resistance of a suction seal when opening a door to a room? This is an example of how the difference in the pressure outside of a space and the pressure inside of a space can influence the airflow within. As with most things in life, air pressure seeks equilibrium. This means that lower air pressure will seek higher air pressure and vice versa.

When considering the key differences between negative pressure and positive pressure environments, there are two main factors: airflow rate and direction.

Airflow Rate

Airflow rate describes the amount of air that travels through your HVAC system. In the Imperial system, it is measured in cubic feet per minute (CFM) or cubic meters per minute (m3/min) in Metric. In order to pressurize a grow room, your ventilation system must maintain a pressure differential, meaning that there is either more or less air being exhausted than being supplied via outside air resulting in either a positive or negative room pressure overall. Mechanical engineers can estimate your air pressure differentials when designing your HVAC system.

Direction

Direction, as it relates to negative and positive pressure, refers to the net airflow. This is the difference of supplied air minus exhaust air. With negative pressure ventilation, the net airflow is negative. Conversely, a positive net airflow will result in a positive pressure.

How To Choose Positive, Negative, or Neutral Pressure Ventilation Systems

There are pros and cons to all types of ventilation. Manipulating air pressure is more commonly applied with grow tents. In our experience, most commercial growers install outside air intake and exhaust systems for use as emergency ventilation to meet local codes or in case they want to flush a room with fresh air.