Replacement furnace size

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mikeb33

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30 year old house in Chicago area with original furnace needs replacement. 1,800 sqft 2 story with partial basement. All windows replaced in past few years and attic has had additional insulation blown in. Current furnace is 100,000 btu. I have a quote now for an 80% and 96% replacement both 100,000 btu.

Question is: does this home still need a 100,000 btu furnace? Even with the 96% model? I would think an 80-90K btu would do? Do the furnace installers think this way or just replace with the same?
 

Jeff Handy

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I live in the west suburbs near Yorktown mall.
I have a great furnace/hvac guy if you are in this area, long time trusted local business.
Let me know if you want his name and number.
 

pjones

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Most likely not required. It would be worth your money to have a reputable contractor preform a proper heat load calculation. They can also look at your ducts at that time and determine if the duct work is big enough to handle the increased CFM of the newer units. If you are able to then you may just kill two birds with one stone by moving down in furnace size.
 

Steve123

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100,000 BTU/hr sure seems rather big to me.
Only way to know for sure is to do a load calculation. They call it a Manual J. If one quoting HVAC company takes the time to do a Manual J, and the other waves his thumb in the air and says "in this size house I normally put a XXXXX", that tells you something about their relative professionalism.
I would suggest you do not consider any furnace that uses indoor air for combustion. For every cubic foot of indoor combustion air that you exit through the exhaust, a cubic foot of cold outdoor air will be sucked into your house.
 

billshack

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when you say furnace is it a hot air furnace, a hot water furnace? also is it electric oil or gas ?
 
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