Yes, even if duct work is inside the conditioned space.
Ducts hidden in wall cavities will typically connect to the outdoors because the sheetrock acts as an air barrier that separates indoors from outdoors.
Some of the largest leaks to outdoors are in two story buildings where joist cavities are used for returns. They connect directly to wall cavities that are open to outdoors causing the depressurization of large portions of the exterior walls, filling them with outdoor air creating huge energy losses. Even worse is that moisture will be pulled into wall cavities leading to mold and fungus growth that degenerates the structural integrity of the building.
In cases where all duct work is clearly visible and contained within the conditioned space, leakage to outdoors will be near zero until interior doors are closed. Then pressures will develop in rooms without returns forcing air outdoors. Simply close all the bedroom doors and repeat the test and you'll measure significant leakage to outdoors which is now caused by whole house leakage paths.
Camera systems to inspect risers, pipes, chimneys, and duct work in buildings
Wohler makes the world's best inspection cameras in Germany. They feature industry leading pan-and-tilt camera heads, video-recording, digital-distance measurement and location beacons.
Ask us about large and small applications, from video borescopes for residential pipe inspection, a more advanced push-camera system with an optional L200 locator for sewer inspection, or a push-rod camera for chimney inspection. These inspection cameras will accurately investigate damage and obstructions then provide detailed reports.