Puzzled with furnace BTUs

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Old 09-29-17, 11:15 AM
L
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Puzzled with furnace BTUs

Looking to replace 22 year old gas furnace. House is a 22 year old colonial (2 zones), 2,500 sq ft., old system is a Carrier 120,000 BTUs. First quote was for a 80 plus efficient gas fired furnace Goodman 120,000 BTUs two stage unit . Second, was for a Bryant 310AAV048090 90,000 BTUs. Haven't contacted the second quote to see why only recommending 90,000 BTUs. Any ideas why the decrease in BTUs? Is this more efficient? Thanks
 
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Old 09-29-17, 11:17 AM
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First step is a manual J or other to determine how much you need. Very common for people to have much more furnace than they need.
 
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Old 09-29-17, 12:18 PM
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Oversizing cuts efficiency and reliability, as well as cuts down on comfort. You'll want load calculations to determine proper size.

Manual J for heat loss and gain
Manual S for equipment selection
Manual D for duct design

You can use this free version of manual J

HVAC Load Calculation - Maunualj - Whole House Loadcalc

Bigger equipment is not better. Many homes suffer from oversized equipment and undersized duct. So it should not be assumed that equipment is correctly sized and the same size replacement installed.
That said, how much did the equipment run in very cold weather?
 
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