Annual Fuel Utilization Efficiency (AFUE)
The Annual Fuel Utilization Efficiency (AFUE) rating is an indication of how well a furnace converts energy into usable heat. The rating is expressed as a percentage of the annual output of heat to the annual energy input to the furnace.
- Low Efficiency: AFUEs below 71 percent.
- Mid-Efficiency: AFUEs between 71 and 83 percent.
- High Efficiency: AFUEs of 90 percent and above.
Ratings between 84 and 89 percent are not common but keep in mind that acidic condensate, harmful to the furnace, forms at these percentages. Public Law No. 100-12, passed in1987, requires that all gas furnaces manufactured after January 1, 1992, have a minimum AFUE of 78 percent.
Atmospheric Vent Combustion
Condensing (or Recuperative Units)
Downflow or Counterflow Furnace
Horizontal Flow Furnace
Installing a New Furnace to Reduce Heating Costs
Even if your older furnace is running fine, you can save large amounts of money by replacing it with a new model. You can even save on your air conditioning by choosing the right furnace. Compared with a 17-year-old furnace, a new furnace can save the average person hundreds of dollars per year. Based on the efficiency of your old furnace, a new furnace can cut your utility bills almost in half. By installing a new system along with a digital thermostat, you will notice even room temperatures, saving energy AND money.
You can choose from two basic designs of furnaces: condensing and non-condensing. The condensing models (this refers to the type of heat exchanger used) are the most efficient and the best choice for most homeowners. The efficiencies of condensing models range from about 90% to over 95%. These models are very efficient, and so little heat is lost in the flue gases that a chimney is not needed. The gases are exhausted by a 2-inch-diameter plastic pipe through an outdoor wall. With no need for a new chimney liner, a condensing furnace is often cheaper to install.
Some models also offer sealed combustion for better efficiency. The combustion air is drawn in from outdoors through another plastic pipe instead of being drawn from inside your house. Being sealed, there are fewer indoor drafts, less noise and less chance of hazardous back drafting.
For the ultimate in comfort and efficiency, but at a higher initial cost, is a two-stage heat output furnace with a variable-speed blower. This type of blower is needed if you want the best central air-conditioning. The gas burners operate at low heat levels, allowing the furnace to run with fewer on/off cycles. The blower will run quietly and switch to higher heat in very cold weather. If your budget allows, we recommend installing an air cleaner, providing allergy relief for your family.