HVAC Duct Sizing Calculator
A crucial tool for HVAC technicians and mechanical engineers. Properly size ductwork using the equal friction method to ensure balanced, efficient, and quiet airflow in any system.
The Lungs of a Building: The Importance of Duct Sizing
The HVAC (Heating, Ventilation, and Air Conditioning) system is like the respiratory system of a building, and the ductwork acts as the lungs' airways. If these airways are too small, the system has to work much harder to push air through, leading to noise, high energy bills, and poor comfort. If they are too large, the air velocity will be too low, leading to poor air distribution. Proper duct sizing is therefore a critical balance, ensuring that the right amount of conditioned air gets to where it needs to go, quietly and efficiently.
The Equal Friction Method
This calculator uses the "equal friction" method, which is the most common approach for sizing ductwork. The principle is to size all the duct runs in a system to have the same pressure loss per unit of length (e.g., 0.1 inches of water gauge per 100 feet). This helps to naturally balance the system, making it easier to ensure each room gets its intended amount of airflow without complex dampering.
The core of this method involves complex charts or a 'Ductulator' slide rule. This calculator automates the process using empirical formulas that approximate the results from those charts. It calculates the 'equivalent round diameter' needed for a given airflow and friction rate, and if you select a rectangular duct, it finds the dimensions that provide the same airflow capacity.