I have an old (25 years) furnace. I think it is a 'keeprite' - no plate but that is what the a/c is and it is original as far as I know.
on the label it says:
'normal input btuh=65000'
'rated output btuh=49000'
so I assume that it means that it is a 65000 furnace delivering 49000 btu's - which works out to 75%. So the 'efficiency rating' I guess is 75%.
So what I am trying to figure out is presumably over time, this number drops somewhat - wear and tear and stuff. Is there any guess what it might be after the 25 years? is there any rules of thumb as to how much these old furnaces drop in effieciency over time?
Just kind of curious.
Thanks in advance