Hi. I'd like to move a couple of heating ducts in my unfinished basement. It seems pretty straightforward. However, the ducts measure 12" x 3 3/8". All of the pre-fab sections I've found are 12" x 3 1/4".
Is this close enough? Am I measuring wrong? Will 3 1/4" sections work? Do I need a stock or custom transition piece?
My house was built in 1955, so maybe that accounts for the difference.