Ducts, Fans and Static Pressure

Once the airflow is known, the duct and fan follow: how fast the air moves through a duct of a given size, how much pressure the run loses to friction and fittings, and how much power a fan needs to move the air against that pressure. These pages use textbook formulas with their sources shown, and any velocity limits are ones you type or ones a named public source states, never a rule of ours. They are estimates, not a fan selection or a duct design.

Tools in this group

• Commercial Kitchen Exhaust Fan Calculator — Enter the exhaust airflow and the static pressure, or add up the component losses, to see brake horsepower, motor kW and energy per year.
• Duct Velocity Calculator — Enter the airflow and the duct size to see the velocity and velocity pressure, or type a target velocity to find the duct size. Switch between cfm and L/s.
• Grease Duct Velocity Calculator — Enter the exhaust airflow and the duct size to see the velocity, or type the minimum and maximum velocity your source gives to see the duct sizes between them.
• Static Pressure Calculator — Enter the length, size and airflow of each duct segment and the fittings to see the friction, the fitting loss and the total pressure loss of the run.