How to Calculate the Size (Ø) and Extraction Flow Rate of a Fan in m³/h:

First, you need to calculate the necessary fan size. There are several ways to determine the desired extraction power based on the room volume. It's worth noting that some methods are more suitable than others and some can be more complex. The following method is well-known and has been endorsed by many growers.

[Extractors: Required Exhaust Capacity of the Fan (m³/h)] = [Volume of the Active Growing Area (m³) x Air Change per Unit of Time (hours) x [Loss Rate - Carbon Filter]

NOTE: When we refer to the cultivation volume, we include the space occupied by the lights and the plants.

To calculate the volume, multiply the length by the width by the height. In our example with two 600W lamps, this results in 1.20m x 2.40m x 2.50m, giving a cultivation volume of 7.20m³. Once you know your volume, you need to multiply it by the air change per hour.

NOTE: For most indoor gardens without air conditioning or CO² supplementation, the "rule of thumb" is 1 air change per minute. In this case, you should multiply the cultivation volume by 60 to calculate the volume of air to be renewed per hour.

Finally, when a carbon filter is attached to the fan, you should expect a 25% reduction in efficiency. This value can vary and depends on the manufacturer and age of the filter, the length and power of the ducts used between the fan and the filter, and other factors. To calculate this 25% reduction, simply multiply by 1.25.

NOTE: Using a filter reduces the efficiency of the fan by 25%.

If we apply the equation to our example of a grow room, it looks like this:

[Required Air Extraction Capacity (m³/h)] = [Volume of the active growing area (m³) x 60] x 1.25 [Required Air Extraction Capacity (m³/h)] = ((1.2m x 2.4m x 2.5m) x 60) x 1.25 = 540 m³/h

The final result is the minimum extraction fan size needed. For example:  150 Ø 150mm with a flow rate of 552m³/h.

Result: 200 Extraction Fan
Duct Ø 200mm
Air Flow: 540 m³/h

If the grow room is located in a well-insulated space, like a basement, using this figure should work well. However, if the grow room is situated in a location that is highly exposed to heat and natural sunlight, such as an upstairs room or an attic, the required extractor size should be increased by approximately 25%.

For a grow room located in an upstairs room or attic,In our case, the closest and widely available extractor is a 200mm extractor with a flow rate of 780m³/h