HVAC Site - Professional HVAC Contractors Forum banner
1 - 1 of 1 Posts

· Registered
1 Posts
Discussion Starter · #1 ·
Hi guys
So I’m doing a job for a client who wants his plenum replaced (due to mold stains)while we replace the air handler. The existing plenum was 5ft tall and 18”x18”.
There was a 8” offset on the previous unit from plenum to the air handler.
Since we are replacing the plenum, I figured out a way to come straight down to the unit without having to cut an offset. The problem is the fiberglass duct board comes as 4ft max height.
This height gives me enough room to add the duct to plenum but the homeowner insist to add the additional one ft piece saying it may effect air flow.
Also in the older plenum there were two flex duct connected across from each other in attic but since the new one is 4ft and we moved it to the right to align with air handler I cannot install them across anymore due to a strut so it will have to be adjacent to each other. (Not on same side but next to each other on each side).

I’m not an expert in airflow and duct work calculation so I can use some help here.

2 questions.
Does plenum height matter? Do I have to add the extra ft? (Old size was 18x18x60 -new size 18x18x48).
Does it matter if flex duct is attached to sides instead of across?

Adding extra 1ft length is not an issue but I want to avoid any additional cut piece if not needed.
Please help.

Sent from my iPhone using Tapatalk
1 - 1 of 1 Posts