Just had new Carrier Infinity furnace + AC coil installed (4-Ton AC/90K BTU heat) to replace 23-yr old furnace. Attic location, (slab foundation) horizontal furnace.
Old furnace intake opening was 25h x 18w. New furnace is 16h x 25w. Instead of adapting existing cold air return plenum to match new configuration, parts of existing plenum were simply blocked off so the intake plenum/furnace union is now about 16 x 15.
I questioned installer at the time and he said if old system had adequate airflow, so would new one. But I'm skeptical as this system serves large downstairs of 2-story house -- 5 large rooms with 10' & 12' ceilings and 1700 sq. ft. total. There are 11 supply registers. House is in Dallas/Ft. Worth.
Can someone please direct me to some guide or info source so I can tell if the cold air return plenum configuration will allow adequate airflow? Before I call heating contractor to come back and reconsider, I'd like to have info to support any concerns I should have. Thanks.