Got a new Coleman 95.5 gas furnace.
The fan is quite a bit noisier than my old unit.
Measures 73 dB in the hallway under the return vent.
That's "C" weighted.
I pulled off the vent covers and measured the airflow
coming out of the rectangular holes in the floor
with a thermocouple anemometer.
I've got 800 linear feet/minute from the 4x10" vents
and 1200 from the 2x10" vents.
With 67F indoor air temp, the air coming out of the
vents is 115F. (my 37 year-old furnace was 150F.)
I added an air conditioner evaporator that provides
additional turbulence to the air flow, but the objectional
noise sounds like blower noise coming out the return vent.
So, The objective is to lower the fan noise.
Looks like I've got plenty of room for temperature
rise due to lower air flow.
I expect I can get the installer to come change the fan motor tap.
What are the pros and cons of turning the fan speed