FAN CFM CALCULATE

Example Calculation:
If we run this equation through our example indoor garden it gives us;

Required Fan size (CFM) = (Volume of Active Growing Space) x 1.33

(8 x 8 x 8.2) x 1.33 =698 CFM

These final figures represent the minimum size extractor you'll need for the growing area in this example. A well-insulated location such as a basement should be fine using an extractor of this specification. Note that less-insulated and more sun-exposed location such as an upstairs, south-facing bedroom or attic will require an extractor around 25% more powerful.

Note that you will need to match your required extractor size to the nearest size available. In this instance the nearest widely available inline fan size is an 8" (200mm) 745CFM extractor.

What Goes Out ...

As we've already touch on, the ventilation method of grow room environmental control is all about replacing the air in your garden. So no disucssion of extraction requirements would really be complete without at least touching on how to get fresh air in!

Growers approach this in two different ways.

Passive air intakes are simply holes that allow fresh air in. The simple act of extracting air will cause the air pressure in your garden to drop so this fresh air will be pulled in through any gaps present. The larger the gaps, the more air. Like water, air will always find the easiest path of least resistance. Passive intakes can take the form of vents or even, at its most crude, an open window or door. We don't recommend this as you want to keep as much control over what comes into your indoor garden as possible-particularly with regard to bugs which can wreak havoc! So by far the best method is to cover all intakes with a bug mesh.

Active air intakes are typically smaller inline extraction fans that blow fresh air into the garden, rather than relying on air pressure. This is preferred by many growers because it puts less strain on the extraction fan and actually helps it to work more efficiently. The intake fan should be connected to an inline air filter to guard against bugs getting a free ride into your garden.