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What are furnace ratings?

Furnaces are rated by the Annual Fuel Utilization Efficiency ratio (AFUE), which is the percent of heat produced for every dollar of fuel consumed. Like the miles per gallon on you car, the higher the AFUE rating, the lower your fuel costs. All furnaces manufactured must meet at least 78% AFUE. If your furnace is 10 to 15 years old, it probably falls well below the current furnace minimum and wastes energy.

Isolated Combustion System (ICS): A New Rating In 1989, the U.S. Department of Energy (DOE) adopted a new, fair way to rate furnaces for AFUE efficiency. Isolated Combustion System, or ICS, is the industry standard that has been designed to reflect the efficiency of a furnace installed in a home setting.

What does this rating mean? The AFUE rating shows the efficiency of a particular furnace. Your contractor can determine your potential cost savings for your fuel costs, annual usage and efficiency. The AFUE rating provides consumers with one consistent number for comparison. Essentially, the ICS test compares “apples to apples.” That is, all furnaces are tested equally. Manufacturers determine AFUE ratings by testing furnaces under set conditions for various lengths of time. The conditions were determined by the DOE to simulate an average home setting.

Therefore, the ICS rating is the best way to compare furnace efficiencies, since all manufacturers must comply with the same testing procedures. So I can just look for a furnace with the highest AFUE rating, right?

Not exactly. The efficiency rating is just one factor to consider when looking at new furnaces. Furnaces use electricity to run fans and motors. The amount of electricity used varies greatly, depending on the type of furnace. Be sure to check electricity usage before making a purchase decision. Other important factors to consider include:

  • How long you plan to live in your house
  • Special comfort needs
  • Fuel availability
  • Fuel cost
  • Geographic area and climate

All these factors, plus your lifestyle and family needs, add up to show you which system is best for you. Let your Lennox dealer show you the best furnace for your home.
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