Has anyone done a combustion analysis on a relatively current furnace? Is a 90 truly a 90? Or are the numbers done in lab-like conditions that cannot be reproduced in real time? any info would be appreciated thank you.

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Is there anyone out there? or is this another do nothing site like most of these discussons


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Hi Randy,

  Very often when completing combustion analysis on 90+ AFUE furnaces, I tend to get a Steady State Efficiencies that are higher than the rated AFUE!  This is because of the likely test location, being at the flue terminal outdoors.  Due to the loss in flue temp, this drives the SSE up.  If you have significantly low SSE start looking for incomplete combustion (too much excess air, too much gas, etc).  I once tested an 80% AFUE furnace that had so much excess air that the SSE was 68%.  When I ripped the furnace out, there was a huge hole in the back of the heat exchanger that I couldn't see with the scope!  Combustion Analysis not only sold the new unit - but maybe saved the homeowner's life!

Good Luck!



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