It is essential to choose the adequate fan for the exhaustion. The wattage of the lamps can be reckoned as a rule of thumb for the performance of the ventilator (i.e. the volume of air processed per hour):

• Lamps with 250W -> Fan with 160m³/h
• Lamps with 400W -> Fan with 250m³/h
• Lamps with 600W -> Fan with 350m³/h

But it is recommended to check the temperature in the growing space to be sure that the extraction is sufficient.

These are the most popular Inline Fans:

Example:
Growing in the Homebox XXL with 2 lamps à 600 W needs at least 700 m³/h and a puffer of 100 to 200 m³ i.e. a fan with approximately 1000 m³/h is recommended.

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Another formula centers on the room volume. This formula is meant for bigger, home-made spaces (i.e. whole rooms). The ventilation of growtents like the Homebox should be determined by the method mentioned above because the development of heat by the lamps is the biggest problem there.

The alternative formula looks like this (in brackets an example for better comprehension)

1. Room Volume
   Height x Width x Length (e.g. 2,5m x 3 m x 2,5m=18,75m³)
   
2. Addition for the Activated Carbon Filter
   The activated carbon filter reduces the performance i.e. we have to add 35% (18,75m³ x 0,35=6,56m³)
   
3. Addition for the air tube
   1m³ per meter (3 Meters tube -> 3m³)
   
4. Performance (volume per hour) of the fan
   The calculated measure is multiplied by 12. In close spaces (growtents multiplication by at least 30 is advisable - but, like mentioned above - in growtents the power and corresponding heat-development of the lamps is the most important factor)
   
5. Result of the example:
   12 x (18.75m³ + 3m³ + 6,56m³) = 339.72m³/h. I.e. you need a fan with a performance of at least 340 m³ per hour.
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