Grow Room / Greenhouse Ventilation Fans, Blowers, and Ducting

About ventilation: A multitude of variables must be taken into consideration when choosing the correct air exchange device to exhaust the air within your grow space. This includes room volume, quantity of H.I.D. light present (air-cooled or open), quantity and size of the carbon filters used, shape of flow path and ambient regional temperatures. A base level air exchange value can be obtained by first determining your room volume by multiplying the length by the height and finally by the width. This value indicates the total volume of your grow space. Your ventilation should be able to exchange this volume in 3 minutes or less as a minimum requirement. Most fans are rated in Cubic Feet Per Minute and is commonly abbreviated C.F.M. Take the cumulative C.F.M. value for all of your fans and multiply by 3. Is this number more or less than your room volume? If the value is less than your base line level you may need to add more fans to adequately ventilate your space. Other factors to consider when determining ventilation demand are as follows:
• Add 5% to your original C.F.M. calculation value for every Air-Cooled H.I.D. and 20% for every uncooled H.I.D.
• Add 25% for the addition of carbon filters
• Add 25% for hot, arid climates and as much as 40% for hot, humid climates