Choosing the right extractor fan for a grow is so important and so easy at the same time. Providing your plants with fresh air constantly is a must for growing quality cannabis. Plants use carbon dioxide and expire oxygen during the day. At night, they use oxygen and expire carbon dioxide. Air in a grow room or tent becomes stale quickly and of no value to plants if not refreshed regularly.

Use circular duct and mixed-flow in-line fans to expel old hot air. Fresh, cooler CO2 rich air should replace old air. This needs to happen every two minutes to keep indoor plants happy. It seems like a lot of air but it really isn’t that hard to accomplish.

Calculating the Volume Of Your Grow

To make sure you select the right fan for your grow, start by working out the volume of your grow room or tent. Multiplying the length by the width and by the height will give you the volume. We’ll use the Lighthouse LITE 1.2m Tent as an example:

1.2m x 1.2m x 2m = 2.88m3 (volume of tent)

Multiply 2.88 by 30 if we are to replace the air in the room every two minutes. This number is then used to compare with fan ratings to select the right extractor fan.

2.88 x 30 = 86.4m3/h

The 86.4 cubic meters of air an hour is the very minimum amount of air your extractor fan needs to move per hour. This will replace the air in the tent every 2 minutes. Avoid problems by selecting a fan rated slightly more than your needs.

Choosing The Right Fan And Filter

Control the smell of a cannabis grow by using a carbon filter. Note that using a filter will hinder the fan’s ability to move air by around 20%. Like fans, carbon filters have different ratings or volume of air they can filter per hour. It’s better to choose one rated slightly better than the fan. By doing this, fans don’t work too hard and will last longer on average.

Putting it all into practice, we’ll use the Ram 4”/100mm Mixed-Flow Fan. On low, it’s rated to move 165m3 of air per hour. Rated at 170m3/h, we’ll use the Ram 4″ carbon filter.

165m3/h – 20% = 132m3/h (Final amount of air moved per hour with fan and filter)

The result is perfect, well above the 86.4m3/h needed and below the 170m3/h the filter can handle.  Meaning equipment will be cruising to replace air in the grow in well under two minutes.

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