Simply calculate the volume of the growing environment to the nearest cubic metre. This is done by multiplying:

Length x Width x Height = Volume of your room in cubic metres (m³) and then multiply the answer by 20.

For example, a room of 3 metres x 4 metres x 2.5 metres high = 30m³ and 30m³ x 20 changes per hour = 600m³ per hour. Once this has been calculated, you can select the correct fan.