DIYbanter - furnace efficiency

"m Ransley" wrote in message
...
how much less than rated efficiency can a moderatly dirty unit burn. ,
5 % , 15 % or 2 %

This is Turtle.

The average furnace will get to about 10% less effency before sutting start to
happen. Then sutting will take it out in about a week. So about 10% would the
point to hold or it will take it'self out. So a 80% AFUE will run untill it
crosses the 70% AFUE rating.

Now as being a little ditry well if you have perfect blue flames and don't have
yellow or white flame of any kind it , it will make very little difference in
the % AFUE rating.

The info was gotten from a fellow checking out the GMP Goodman furnaces for a
defect in the burners as the Flame sencer cutting the furnace or shutting it
down on cold morning starts and goodman put out a replacement becket burners to
stop the problem. The burner was not the problem but they were letting the
plastic cover that help seal the fire chamber blower motor blower housing attach
to the furnace wall drop down and flap in the blower air coming out of the
burner tubes going into the blower wheel. All you had to do is remove the
plastic or just pull the blower fan motor wire off and let the furnace go out on
the high limit and it would melt the plastic and fix it. Now it was a better
ideal to get the newer becket burners for it would make it a 81% AFUE out of the
old burners or the furnace which was a 79.1% AFUE furnace. The Old burners was
not letting enough air in and was getting almost the 400 ppm CO coming off the
fire chamber. No one said a word to Goodman for having the 79.1 %AFUE when it
was suppose to be the 80% AFUE.

TURTLE