Ideally, your growing environment should be under Negative Pressure; this is to prevent any air escaping from the growing space.
Most growers will use either: 1x Large Extraction fan and a passive inlet OR 1x Large Extraction fan and 1x Smaller Intake fan. Either one of these setups will create negative pressure.
If you’re using 2x Fans of the same size & power, then you may end up with Positive pressure.
If you want greater control over the Negative Pressure, then the G.A.S EC Fan Balancer is what you require!
Plugged in between the EC Fan Controller and the EC Fans, the EC Fan Balancer has been designed specifically for EC Fans ONLY, and will control the Maximum Speed of both the Intake & Extraction Fans.
2x Fans of Equal Size: You would set the Minimum Fan Speed (for both fans) on the EC Fan Controller, and set the Maximum Speed (for each fan) on the EC Fan Balancer by having the Inlet fan at a lower Maximum Speed than the Extractor Fan
Fans of Different Sizes: This is only used when the user wants more control over the Negative Pressure within the growing space. You would alter the Maximum Speed (on the EC Fan Balancer) for each fan, until the desired Negative Pressure is achieved.