how to size a high efficiency 2 stage furnace replacing a single stage 90,000 BTUs natural draft furnace. How many btus needed for new high efficiency furnace
thanks
Where is the house located and how old is it? And what is the input/output of the existing furnace?
Without a heat loss calculation it won't be scientific but I can probably get you in the right ballpark.
its in Malton and build before 2000. 90,000 input to 82,ooo btu out
other calculations are typically done like duct sizing, sq footage and heat loss but if youre replacing it with lets say a 96 AFUE furnace then an 80k would output 76800k which is close to the output of your old appliance on high fire.
THATS JUST A GUESS, never just plop in whatever the last furnace was cause you dont know if THAT one was sized correctly