According to the 2015 IECC, (International Energy Conservation Code) a duct leakage test is required when any part of the duct or the air handler sits outside of the building envelope.

The ductwork can be tested either at the rough in stage with or without the air handler or in the post construction stage. The acceptable air leakage is 4 CFM, (cubic feet per minutes) per 100sf when the test is conducted either with the air handler or in the post construction stage.

When conducting the test without the air handler acceptable air leakage is 3 CFM per 100sf.