How to Calculate a Ventilation System

how to calculate a ventilation system

Environment is everything for indoor cultivation, starting with your ventilation system.

Undoubtedly the most important pieces of equipment for a grow room, growers can use top of the range lights and the best nutrients money can buy – but without a reliable and functional ventilation system, the plants won’t yield productively. A grow room ventilation system deals with four main environmental factors:

  • Removing heat created by the lights
  • Delivering fresh, CO₂ rich air
  • Removing humidity from plants
  • Maintaining negative pressure to stop odours escaping

How to work out what you need

Size up your grow room

Start by measuring your grow room in metres. Once you’ve got your length, width and height, multiply together to get the volume of your grow room.

For this example 2.4m x 1.2m x 2m = 5.8m³ total air volume.

Total volume of air

Then multiply the volume by 60 to give you the exact air flow you need to change the air every minute.

Total Volume
To change the air every minute, multiply by 60: 5.8 x 60 = 348m³/h.


For this size grow room we would suggest a Revolution 150 EC fan (maximum air flow 796m3/h) with a 60-150-660 CarboAir filter – adding a carbon filter reduces the maximum air flow to 655m³/h.


The airflow of your intake fan needs to be at least 25% less than your outtake fan.

You can calculate your intake fan by multiplying your maximum outtake by 0.75, which in this example would give you: 655m³ x 0.75= 491m³

The perfect intake fan to maintain negative pressure would be a K125EC.

Alternative method

An alternative way to determine what air flow you need is to allow 300m³/h of air flow per 600 watt HPS light. If your grow room is an unusual size or shape that’s difficult to measure, this method can be used.