"Jack" wrote in message ...
Nothing blocking it. No pipes above it. There are flexible branches that
are up in the joist space. It is a straight-shot for about 25 feet.
.
Edwin, I don't understand what you mean when you write 'shorten the duct
on one end, lengthen the other end'
.
Thank you for your time.

I was not clear there. Not the duct being raised, the ones it is attached
to. If it goes up to the floor above with an elbow, the duct it connects to
must be shortened. Same at the other end if it is coming from the furnace
and making a turn. Depending on the setup, possibly an "S" turned piece to
join the low and high parts would do. Is that what you mean by a transition
piece?