?

Ratings are based on input. Assuming a 100,000 Btu unit of 80% efficiency,
20,000 is going up the flue, not into your house. With a 100,000 Btu unit
of 90%, only 10,000 is going away, so you have an extra 10,000 going to heat
your house. Thus, a reduction in capacity will give the same amount of
heat.



Is that true?????

I thought furnace ratings were based on OUTPUT...i.e

a 100,000 BTU/Hr 90% furnace DELIVERS 100,000 BTU per hour.

and a 100,000 BTU/Hr 70% furncae also delivers 100,000 BTU/Hr but takes
more fuel to do it.

Correct?

My York (warm air oil fired) furnace nameplate says Bonnet BTU =
100,000 which I thought refers to the output not the input.

Correct?


Mark