First floor system might be oversized
I have a question about our first floor system. We have a 2012 Trane XR15 3.5 ton H/P matched up with a 2013 Lennox SL280v 90,000 BTU input two-stage variable-speed furnace with a 4 ton blower. The first floor is 2,200 sq. ft. I don't understand why the tech did a load calculation that came up to 3.62 and the current ductwork can't handle 1400 cfm. So basically the furnace runs around 1060 cfm the first 7 minutes, then ramps up to 1220 cfm. Both installers said we are fine on return air, which I HIGHLY doubt it. You can hear a loud whining noise when the blower is at the higher speed. We called a tech out and he lowered blower speed due to the fact our current ductwork can't handle 1400 cfm (He said current ductwork can hold around 1150 cfm's on the supply side and 1080 on the return side) and to help solve the noise issue. The system still cools and heats great even with the blower speed set at the current speed. Question is, can too little airflow hurt the performance of the system? What can be done to solve the issues? Thanks.