Using a 24″ x 36″ sheet of (intended for ducting) sheet metal (~$10) and rivet tool + rivets (~$15) I was able to take a 14″ x 8″ opening and create a 4″ deep reducer down to a 14″ x 4″ opening.
This way, this can be an insert into an existing duct and “boot”/box that takes an 8″ pipe of heat into a 4″ deep 14″ x 8″ box. It can then exhale the heat into a 14″ x 4” vent.
Why the insert you ask? Hint: house was built in 1960. Guess what the most common way to insulate ductwork *and* boxes/registers/boots was back then? ASBESTOS, YAY!
So while we don’t know it is for sure, it sure looks like it (inspectors clued us in, t00). So we not gonna mess w/ the box/ductwork that is in relatively good shape and not cut it, etc.
This is all part of a Bigger Project of redecoration we are doing at the bunny fort…