On Nov 5, 7:40*pm, mm wrote:
I think I understand why new furnaces are more efficient, but why AC?

I finally read an explanation about the exhaust air being cooler, as
low as 90 degrees F from gas furnaces, and more heat extracted from
the fire to heat the house, in new furnaces. *I presume new oil
furnaces are more efficient the same way.

But why are new AC's more efficient. * There is no cold air going up
the chimney with an old AC. *I presume that if the refrigerant doesn't
lose all its coldth, warm up to room temperature, in the AC evaporator
inside the main air duct, when it returns to the condensor, it's that
much easier to condense because it is colder, and less heat has to be
radiated out from the condensor fins. *So iiuc there is no loss there,
at least if that pipe is insulated.

So why are the new ACs more efficient?

The same reason new refrigerators can be 75% more efficent than units
30 yrs old, they were designed with efficency, not profit, as a goal.
www.energystar.gov