HELP! MY HVAC DUCT IN THE ATTIC IS LEAKING! In this case critters had chewed a hole in the outer liner of a duct; fortunately it did not penetrate into the inner layer. We were able to patch it since the inner liner was intact. Usually with a hole in the dark we need to replace some of it. The photo on the right shows the duct before repair. Left photo shows the restored duct.