On Fri, 21 Jan 2011 05:12:08 -0500, "JoeSpareBedroom"
wrote:

How old is this furnace?

31 years. I thought I was the last one using the original furnace,
but asking around I have found at least 3 others of the 109 of us.

I also found the original instructions on-line and dividing output
btus by input btus, it was 80% efficient. Not sure what it would be
cleaned or uncleaned now. The Bryant they sold my meighbor last
summer has an EPA label that it's 81.5% efficiient.