I am considering modifying the supply on my vapor fire later this spring. I currently have a 12” coming off the top and another 12” coming off the front with a 90 degree elbow into my trunk line. I would switch this to a single 16” off the top and repurpose the hole in the front of my plenum by wiring in a normally open power closed damper for power outages. I typically fill my firebox full and the furnace stays on small c for a decent amount of time beginning an hour or so into the burn. Losing power at this time wouldn't slow the burn since the furnace is already running on pilot. Anyways, I feel this is likely a worthwhile addition in my case.
My question is if I have anything to gain from going from the two 12’s to a single 16”? Air flow coming out of the registers isn't an issue with the blower wired to the low tap so I guess I am asking about duct temp loss. I read somewhere online that a 12” 90 degree elbow in the duct work is equivalent to 25-30 ft of straight pipe. Could I be losing any air temp from this 90?
![[Hearth.com] Reconfiguring Vapor Fire Supply](https://www.hearth.com/talk/attachments/img_7628-webp.337368/ "[Hearth.com] Reconfiguring Vapor Fire Supply")
My question is if I have anything to gain from going from the two 12’s to a single 16”? Air flow coming out of the registers isn't an issue with the blower wired to the low tap so I guess I am asking about duct temp loss. I read somewhere online that a 12” 90 degree elbow in the duct work is equivalent to 25-30 ft of straight pipe. Could I be losing any air temp from this 90?
