"HL" wrote in message
news:tNurd.223772$df2.120623@edtnps89...
Compared to a 20 year old furnace how much does each design improvement
increase AFUE:

Draft inducer fan
Ignitor vs pilot
Faster fan startup (is this due to the draft inducer)
Hx design chages?
Anything else?



Yes.

The biggest improvement, IMO, is the ignition vs. the standing pilot.