I’m working on a project to install new forced air furnaces within a large apartment complex.  Each furnace is 100% within each unit’s conditioned space.  It’s a heating only climate.

The City inspector is saying we still have to duct seal and insulate all the air runs and have the ducts professional pressure tested.

I’m having trouble figuring this out.  If the return side leaks, it just draws more conditioned air into the furnace.  If the supply side leaks, it just heats the unit.  I can’t see how the carbon or installation cost of adding bubble wrap or sealing the ducts could have a payback in this case.

This would be different for an attic or crawl installation.

What do people here think?