I recently had a 2.5 ton upstairs unit replaced with a 5 ton. The installer added a 14" return to two existing 8" returns. The 14" only has an inlet opening of 12X14 due to existing electrical obstructions. No supply ducts were added. The new AHU has three oulets. One is a 16" supplying two 12" ducts. One of these 12" ducts feeds two 8" and one 6" ducts. The other 12" feeds one 8" and one 7". Another 8" outlet supplies one 8" duct. The last 8" outlet supplies a 6" and 5" duct. The 8" and 7" ducts have 6X14"" registers. The 6" ducts have 6X10" registers. The 5" duct has a 4X8" register. This unit is cooling approx. 1500 ft2 plus a foyer (1700 ft3) that gets very hot in the DFW heat. He set the VS blower to run at 450 cfm/ton to help cool this area and augment my 21yr old downstairs units. The unit is also set up in comfort-r setting. Humidity removal is decent (60%). However, the wind noise at the registers, esp the undersized return is quite noticeable when blower goes on high speed. He knew this might be a problem at the current blower speed setting. Backpressure? My main question here is how can I determing if I need to add either return/supply ducts and if so, how many/size? The unit currently cycles on the small compressor with the 5 ton running only occasionally. Run time is 12hrs/day. It seems to me a unit capable of moving up to 1800-2300cfm needs more ducting. I'm running a disposable fiberglass filter upstream of a Honeywell F300E EAC. After approx. 300 hrs of runtime both are still fairly clean.
I'd like to get some educated opinions before confronting my HVAC guy. Is this system being optimized?