Duct Leakage Testing
The test is performed by sealing off the duct system and attaching a calibrated fan system. In order to pressurize or depressurize the system it's necessary to seal off all known openings. Until the invention of Vent Cap Systems, this had been done with custom, expensive, disposable plastic tapes. Many attempted to lower costs by using sandwich wraps like Press N Seal or even time consuming blue painter's tape Once the known openings are accounted for and sealed, the fan speed is increased until the pressure inside the systems has reached the relevant standard pressure, typically 25 or -25 PA. Depending on the size of the system, it should only take a certain amount of air flow to reach the required pressure. Any air flow over that amount is leaking from somewhere and the amount can be quantified as a percentage with current codes mandating 6% or less.
If the system is too far gone it's possibly not worth repairing, but in most cases the systems can be tightened up quickly. A typical system can be repaired & sealed up quickly - depending on size and severity - potentially saving a hundred dollars or more a month, extending the life of the air conditioner, and improving homeowner comfort. This gives duct leakage testing, and its associated repairs, the highest return on investment of any energy efficiency upgrade, dramatically outperforming added attic insulation and windows. This increased efficiency, the decreased demand on public utilities, and savings that disproportionately benefit lower income earners, have bolstered bipartisan support for mandated testing and improved building standards. Duct Leakage Tests, and Home Performance Testing in general, are the new "home inspection" and are here to stay and will probably be federally mandated before long.