Oh, we,definitely are. This guy did our neighbors, including changing their return ducts! I couldn’t believe it.
Funny thing is, this housemate was built in 1952 with zero insulation anywhere and incredibly leaky steel frame windows. We’ve insulated everything, new windows, and sealed leaks. So JT eneating and cooling load is far below what it was when the house was new. The ducts at the time were sized to handle the heating load airflow and no AC in an uninsulated drafty house.
I’m not buying what they are selling.
I’m not buying the return duct story. If it worked adequately for 30 years, it still will.
Lower delta-t is trade jargon, did they explain it? Because if you have, say a 20 degree drop in temp across your coil (delta-t, say 80 deg in, 60 deg out) at a given air flow, if you increase the flow over that same coil, that delta-t will drop (say 80 deg in, 65 deg out).
I say their selling you a bill of goods.