I have a Bryant 80 series gas furnace. I think it's from 1973.
It's in a doublewide mobile home.
The past owner must have destroyed the original round crossover furnace duct tubing.
They put in it's place cheap foil type tubing (don't know what to call it) and it's like 8 inches which I assume can affect the pressure of air coming out vents to be less and make the unit work harder overall.
It was jerry-rigged with duct tape to stick up onto bottom side of furnace opening which is a round 6 inches in diameter. And it's fallen off.
I want to replace it with proper aluminum or steel tubing of correct size.
I am "assuming" that whatever the diameter of opening on bottom of furnace for the cross over furnace duct tubing, is what I should stick with all the way across and into other side of home.
In other words, is there such a thing as having a 6 inch opening, and having to upsize (or downsize?) it to another diameter to keep it in specs with the model of furnace for pressure and CFM reasons?
I would think if it needed such upsizing then wouldn't the manufacturer just make the opening on furnace, the size it needs in first place?
So what I want to know is should I make all the duct tubing the same diameter as the opening in furnace or is there reasons this is not always true?