BTU and Efficiency Question

[jetpilot500]

I was wondering (theoretical question):

If I had a 100,000 BTU Furnace that was only 70% efficient could I replace it with a 70,000 BTU Furnace that was 100% efficient?

[psychometric]

Yes

[icyflame]

Yes

[jetpilot500]

Great! Thanks!

[docholiday]

still some if's.

What if you only needed 55,000?
Also, you would want to consider that a 100,000 btuh furnace at 70% efficient with little off time probably runs a slightly higher efficiency. It would have a lower efficency with long off cycles.

[BaldLoonie]

Even though the AFUE may be 70%, the actual output steady state is 80% of input. So running 24 hours a day, that sucker is putting out about 80K per hour, not 70.

[amd]

Most natural draft furnaces are around 60-65% AFUE and 75% steady state output. Read the rating plate to determine what the output is, and never sized based on current equipment. (current unit could be too large)