Return air Multi-Duct run Placement and design questions

[acguytx]

BTW i tried the one side cut AND ONE ON END on a furnace ON AN INSTALL BUT THEN I WAS CONFUSED ON HOW TO MEASURE THE static on the return with this method because you can really get between filter and furnace for proper location to measure or can you?

[nvr2old]

Here's an install question. If your furnace opening is 23x14 and you 5 inch filter rack is 20x25 do you make a transition or do you butt the rack up against the furnace and blank off the excess opening on the rack?

[acguytx]

Here's an install question. If your furnace opening is 23x14 and you 5 inch filter rack is 20x25 do you make a transition or do you butt the rack up against the furnace and blank off the excess opening on the rack?

well we all know you are supposed to use a transition simply because not having a smooth airflow its like surface area of a 90 added to Friction rate to equivalent length, however most just blank it off secondary option is to use a 16 x25 base ..