Warm Air Furnaces are units that move air through ductwork that blow the air from registers or vents throughout your home. There are many different brands and styles, with varying levels of efficiency. With advances in technology, newer furnaces can achieve 97% Annual Fuel Utilization Efficiency (AFUE). That means for every $1.00 you spend on fuel, $0.97 is put into heating your home. 

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​Many of the furnaces in homes today are of the 80% variety which can lead to higher utility bills, and they rely on the air inside your home. High efficiency furnaces use the air from outside your home for combustion making the furnace more efficient.