Static Pressure Balance and the 20 Rule Drive HVAC System Efficiency Through Proper Duct Engineering

https://wakelet.com/wake/i5-r2m057q2bZJ-xvpKt1

The 20 rule in HVAC refers to the requirement that return-air duct size must be at least 20 percent larger than supply-air duct size to maintain balanced airflow and prevent static pressure buildup