A duct leakage tester is a diagnostic tool designed to measure the airtightness of forced air heating, ventilating and air-conditioning (HVAC) ductwork. A duct leakage tester consists of a calibrated fan for measuring an air flow rate and a pressure sensing device to measure the pressure created by the fan flow. The combination of pressure and fan flow measurements are used to determine the ductwork airtightness.
During the construction process, when the duct is accessible before the grilles and equipment is installed, each intentional opening in the duct system is sealed air tight with plastic and tape. The duct system is then placed under high pressure, and the airflow through the fan is measured. The fan airflow is interpreted as duct leakage. If the level of leakage is out of spec, the leaky duct is repaired and then the test is repeated. The process continues until acceptable results are achieved.
Higher pressure is critical to assure the pressure at the fan is equal to the pressure throughout the entire duct system. Only then can the pressure at the fan be interpreted to represent accurate airflow leakage throughout the system.
Since air is the fluid that carries the heating or cooling throughout the building, its flow, temperatures, velocities, losses, gains, and enthalpy must be verified at many points throughout the system so it can be effectively diagnosed and performance rated.
Airflow is the life-blood of a system upon which all the other components and circuits depend. Air is as essential to the system as power is to the fan. Without verification of airflow throughout the entire system, it’s impossible to effectively test the heating and refrigeration performance.