# Improving furnace AFUE

How much would the following improve efficiency? (20yo gas upflow in the basement)
1. Make the furnace room airtight and add outside combustion air. This would eliminate heated air from going up the chimney. There is already CA to the return but this may not be enough.
2. Turn off pilot when not in use - 8 months/year
3. Increase the speed of blower by changing pulley
4. Set fan Limit switch to start fan sooner and stop later
I know the newer furnaces are 80-96% but I spend < \$800/yr on gas so the payback will be too long.
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1 maybe 5\$ a year. 2 maybe 8 \$ a year. 3 zero, and your fan may not last and electric should go up. 4 ? maybe zero. Payback? how long will you live there. If you are very lucky you are at 80%. and a 94.5% unit will save 18%. So say you are at 75% a 94.5% unit will save apx 26% and that is at todays gas prices, in ten years gas will probably be double
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I believe it's (old afue - new afue) / new afue lowering the savings to 15% and 21%.
http://www.aceee.org/consumerguide/reheat.htm
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HL there is no "old Afue" , recalculate using the 80% furnace as a base for 100. . 80 is the baseline, so what is say 5 % of 80, more than of 100 get it ??? Or figure the % difference of the 2 units on each other, not 100 as a %
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would
If you are spending that amount on gas, your payback will be quicker....do the math.
also, nothing you state above is worth your time, effort, and 3 and 4 are bad for you.
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Aren't the 80% AFUE furnaces supposed to eliminate losses cause by the pilot light and 24hr of paid heated air going up the chimney? Would not 1 and 2 eliminate most of those losses? Much efficiency loss would appear to be caused by 2+ mins of burn before the fan comes on followed by 4 mins run time. I suppose the new draft inducer design and faster fan startup eliminate most of this.
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You are forgetting electric blower consumption, an old unit may take 450 watts on low, mine did, my new unit takes 325, and a VS unit can take 200 or less. You will increase AC seer by 1 with a new VS unit and save winter and summer on electricity, Now payback is a new calculation of much less time.
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Most are much less, particularly if DC....

Incorrect. You can loose SEER ratings unless the entire system is set up, and MATCHED. You start throwing VS motors on units and unless its been correctly set up , all kinds of things can start to happen.
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CB ,what can happen, Im taking out a 2 speed 2 stage, 3 year old furnace , all was new at the same time, putting it in the garage and getting a VS DC. My AC is oversized since I insulated after the AC install and a new smaller outside compressor is out of the question. The original lennox guy was going to do it. The only thing I was told about was freezing the coil on lowest speed , So If I get it instaled- matched right I will be OK? Or what is the salesman not telling me . And " who" is Hack`n Dave`s in Illinois .
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just as bad throw VFD controls on the existing motor. VFD/VS should be matched together for best performance.
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After the 20 years of service this furnace has more than paid for itself. Your now running on borrowed time. It's time for newer high efficiency furnace. All the suggestions by the other tech's is true and correct. If you are experiencing \$800 gas bills from the heating system alone, a 96% furnace will pay for itself actually in a short time.
--
Zyp
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