I found a large hole (~10cm x 10cm) cut into one of the HVAC ducts that supply the bedroom. It was cut between the duct and the joist and is not visible from the ground, I found it attempting to diagnose efficiency issues with the system.
The duct itself is not insulated and has close to square cross section.
How should I go about making a repair?
The results I've found online tend to be related to fixing small / minor cracks with mastic or tape.
My thought is to purchase a length of ducting, tape it in place then insulate it.
- Edit 1: Add two pictures of the duct. From below and from above (between the duct and the joist. Add a description of the duct.