What size furnace for 2000 square foot house?

2000 sq. ft. x 5o (based on climate zone)=100,000 btus so; between 80k-100k

(100,000 Btu's needed) 80% Efficient furnace: 125,000 Btu capacity; 90% Efficient:

110,000 Btu capacity; 95% Efficient: 105,000 Btu capacity.

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http://www.gasfurnacepricesonline.net/22/what-size-furnace-do-i-need-for-a-2000-square-foot-house/