Extraction and Ventilation Fans

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Ventilation, extraction and intake fans are an important part of keeping your grow room well ventilated as plants need fresh air to grow. Fans are another way of controlling your room temperatures too.

What Size Fan do I need in my grow room or tent?

To calculate the size of fan you require simply follow these instructions:

Measure the Height, Length and Width (in metres) of the growing environment.
Multiply (H x L x W) to give you the cubic meter volume.
Multiply this figure by 25.

This is the size of fan required to change the air 25 times in an hour.

There are some other factors to take into consideration, such as:

Multiple lights in your room – you are producing more heat in the same space than you would with one light.
Carbon Filter – If you are planning on using a carbon filter, please allow for a 20% reduction in your airflow.
Ducting – Every bend in your ducting is restricting your airflow by at least 20%.

Buy the fan slightly above the figure calculated if possible to ensure adequate ventilation.

It is very important to replace the air being extracted from your room. The intake fan should be placed low down inside the room to allow the air to circulate and rise through the foliage. This will also cause the hot air to rise towards the extractor fan.

Your intake fan should always be at least one size smaller than your extractor, creating negative pressure within the room and aiding with constant air replacement. E.g. if you are using a 5” extraction fan for your room, a 4” intake fan would be ideal to use in conjunction with this.

How do I know if my ventilation is wrong?


Temperatures too high
Humidity too high
Mould, mildew or bud rot


Tent walls being sucked in/blown out
Humidity too low
Temperatures too low

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