How to setup Weed Grow Room Ventilation

An indoor garden’s ventilation system supplies all of the fresh air (which supplies CO2 to gardens without CO2 enrichment systems) and removes stale, hot air from the environment. Ventilation systems can be as basic as a couple of fans or as complex as a series of blowers, air conditioners, dehumidifiers, and atmospheric controllers. Regardless of how elaborate your ventilation system is, the purpose is the same: to keep the temperature and humidity in the growing space within the desired range and as uniform as possible.

Intake and Exhaust Fans

Even the most basic ventilation system is usually equipped with intake and exhaust fans. The intake fan’s purpose is to draw fresh air from outside (or from a space outside of the growing area). Typically, an indoor horticulturist will want to filter this air to reduce the likelihood of pathogens or insects. HEPA filters (or even a nylon stocking stretched over the intake port) will work for this purpose.

In most cases, an intake fan is set up to work in conjunction with an exhaust fan. The exhaust fan is typically slightly larger than the intake fan. This is to ensure a slight negative pressure so that all odor from within the garden is forced through the exhaust system when exiting the garden. The exhaust fan’s job is to remove the stale, heated air from the garden space and, when connected to a carbon filter, to also remove odors as the air is exhausted. Intake and exhaust fans can be set up on timers or connected to thermostatic controls. Thermostatic controls offer more control because the grower can set his or her desired temperature for the grow room and the fans will be turned on or off automatically as needed.

Air Conditioners For Growing Weed

Another common component found in many indoor gardens’ ventilation systems is an air conditioner. Air conditioners are useful tools for medical marijuana growers because they can help to control heat created by intense grow lights much better than fans alone. Air conditioners should be sized dependent on the amount of artificial lighting being used. A very general rule of thumb is to assume 5,000 BTUs of cooling capability is needed per 1000 watt lighting system. In other words, a 10,000 BTU air conditioner would be a good fit for a room with 2000 watts. The type of reflector (air-cooled or not) and the size of the exhaust and intake fans will also influence the size of air conditioner needed. Also, the ambient heat of the room itself affects heating and cooling requirements. In other words, a grow room in Alaska compared to a grow room in Southern California will have different heating/cooling requirements.


Medical marijuana growers should always incorporate oscillating fans within the growing space to make the temperature and humidity as uniform as possible. Medical marijuana plants thrive on consistency and the grow room’s temperature and humidity are no exception. Air movement within the growing space will also help strengthen the structural integrity of the plants, making them more capable to handle large flowers. A working ventilation system is one of the key components to creating a successful grow operation. Medical marijuana growers who take the time to set up a well-functioning ventilation system will receive a larger return on their investments harvest after harvest.

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