Here, I googled it for you.
"[...] The DOE's technical definition of AFUE is as follows:
The measure of seasonal or annual efficiency of a furnace or
boiler. It takes into account the cyclic on/off operation and associated
energy losses of the heating unit as it responds to changes in the load,
which in turn is affected by changes in weather and occupant controls. "
I will have to ask my friend who taught HVAC. He said more efficent is
better, and likes 90+% variable speed furnaces, but did note going from
my present 69 to 93 will NOT cut the gas bill by the percentage it
appears. Have several friends who replaced their furnaces and noted
exactly the same thing.
Bill went down but not as much as anticipated:(
heat pumps cost way more to operate than forced air gas
Your gas bill isn't proportional to your gas usage. There are other
charges besides the gas charge. Additionally, if you have other gas
appliances, then you have to prorate your fuel usage accordingly. You
can't just take the total bill and multiply by 24% to get the estimated
energy savings for the new unit. Sorry, but it isn't that simple. :)
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