Duct testing, also known as duct leakage testing, involves sealing off the duct system and attaching a calibrated fan system. (eg. Minneapolis Duct Blaster™ by The Energy Conservatory or Retrotec's Duct Tester) To pressurize or depressurize the system, it's essential to seal off all known openings. Until the invention of Vent Cap Systems, this was typically accomplished with expensive disposable plastic tapes. Some attempted to reduce costs by using sandwich wraps like Press N Seal or time-consuming blue painter's tape.
Once all known openings are sealed, the fan speed is increased until the pressure inside the system reaches the relevant standard pressure, typically 25 or -25 PA. Depending on the size of the system, it should only take a certain amount of airflow to reach the required pressure. Any airflow over that amount indicates leakage and can be quantified as a percentage, with current codes mandating 5% or less.
While a system that is too far gone may not be worth repairing, in most cases, systems can be tightened up quickly. A typical system can be repaired and sealed up quickly, potentially saving a hundred dollars or more per month, extending the life of the air conditioner, and improving homeowner comfort. Duct leakage testing and its associated repairs offer the highest return on investment of any energy efficiency upgrade, significantly outperforming added attic insulation and windows. This increased efficiency, decreased demand on public utilities, and savings that disproportionately benefit lower-income earners have led to bipartisan support for mandated testing and improved building standards.
Duct Blasters or DucTesters - used for pressure testing the duct systems to check for leakage. Current standards dictate that the duct system should leak less than 5%. Some figures pegged the national average over 25% - a 20% reduction would make for SIGNIFICANT savings.
Blower Door Systems - large fans inside adjustable frames, built to fill open doorways, are used to depressurize the entire house allowing you to literally observe air infiltrating a home near plumbing penetrations, outlets, and framing for doors and windows.