Does it matter what type of return air drop I used when I install a new high energy efficiency gas furnace(95%)? Do I reused my old one installed 18 yrs ago. I plan to get a filter rack. The duct work used was not customized; just used stock duct work. I see that there are return air assembly where the boot is curved and some are slanted. Mine is just "L" shaped. One dealer said it matters and another said it doesn't whether you use curved or slanted, but appears to matter. The one that said it matters said that a curved boot provides less turbulence.
I read on one duct work dealers site the following: "High efficiency right angle filter assemblies allow the installer to offer a 20" X 20" X 5" filter cabinet with a furnace cut out dimension of only 14" X 23". The filter is positioned in a drawer at an angle. Reversing panels allow for left or right handed installation."
So does it matter?