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Air Exchanges Per Hour

What do you think is the optimal amount of air exchanges per hour in a non CO2 indoor grow room?

I have gone back and forth on this and have too many variables and other needs to have a definitive answer and could use some input. Right now I’m doing 2-3 exchanges per hour. I have enough HVAC to stay cool with constant exchanges.


You should be able to exchange the air in the room in 15 minutes, do the math for cubic feet, I.E., 1000 cobic ft = 66.666 ft. per min…


When it comes to “Total air changes”, so long as you are not toppling the plants and the air is well distributed, more is better. Along with acceptable Vapor Pressure Deficit, airflow inhibits the formation of micro-climates.

When it comes to “Outdoor air changes”, they are needed to keep CO2 at acceptable levels. This is a function of how much oxygen the plants are producing and this varies daily and with stages of growth. Therefore, in the interest of conserving energy, the amount of outdoor air should be regulated based on the CO2 or oxygen level of the room.



We generally see exchanges every 3 minutes or so in sealed room setups. The only time they trend higher is in extremely tall rooms where ceiling height is over 16’ or if the area is massively under lit.

Brandon Kion
Excel Air Systems


6 times per 12 hours if using Co2
2 times per hour no Co2