View Full Version : Plenum and takeoffs

08-04-2008, 09:30 AM
I am installing a new furnace and plenum. The main trunk line and old plenum/furnace are 24" wide. The new furnace is 21" wide. The question is should I reduce the main trunk from 24" to 21" and tie it into the new 21" plenum or should I make the new plenum 24" wide and reduce it down to fit the 21" furnace? Thanks.

08-05-2008, 06:22 AM
Nick67........why change anymore than you have to????????Transition from 24" down to 21" Leave as much of the existing duct as possible....

08-05-2008, 08:15 AM
I agree! You'll save a lot of time and money!

08-05-2008, 12:47 PM
Thanks for the advise.
I didn't know if the smaller transition off the plenum into the larger trunk line would screw up the air flow.