|
QUESTION:This may be a simple question, but is there any rough rule of thumb about
the efficiency of old furnaces. We just replaced a 31 year old forced air
gas furnace that was rated at 200K input/160K output, making it 80%
efficient. Are these numbers consistent with today's ratings for
efficiency? I'm wondering if it could really have been what was considered
to be an ultra high efficency model for it's day (the equivalent of a 94%
one of today), which would mean that our energy costs wouldn't shrink
appreciably. The new model is an 80% 140K btu model, and it seems that it
runs longer than the old one did (of course we are having dead of winter
weather and it's still fall, yikes). Or is this the way the newer models
are designed to run, which may alleviate temperature gradients and swings
between cycles?
ANSWER: One thing to remember or know about stack furnaces is that they are
rated at their efficency in a Lab with only a 4 foot stack in steady
state conditions. In the real world they are even more energy hogs
compared to condensing furnaces with external air for combustion. When a
stack furnace shuts down it continues to steal you blind whereas a
condensing furnace shuts down and isolates. This even has a partial
affect on summer a/c load.
|
|
|
|
