Condensing Gas Furnace: What Makes It So Efficient?
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Condensing Gas Furnace: What Makes It So Efficient?


As a Portland-area homeowner, you probably already know that energy efficiency is not simply a noble gesture toward conserving natural resources; it can lower your fuel bills, too. A condensing gas furnace is one of the most efficient ways to keep your home and family warm.

Efficiency by the Numbers

Furnace efficiency is measured using Annual Fuel Utilization Efficiency(AFUE), a metric that allows quick comparison. Standard furnaces 15 to 20 years old probably achieved around 65 percent AFUE. While modern conventional furnaces can achieve around 80 percent AFUE, condensing gas furnaces can climb to a whopping 98 percent efficiency.

Follow the Heat

To achieve such astounding fuel efficiency, a condensing gas furnace recaptures heat from combustion by adding a second heat exchanger to the process. The cold air return draws air into ducts, through a high efficiency air filter, a blower (this could be variable speed for even greater efficiency) and over the first heat exchanger.

The air gains thermal energy and passes a second heat exchanger, and here’s the heart of the difference between a regular furnace and a condensing gas furnace. Combustion exhaust gases heat the second heat exchanger, wringing every bit of thermal energy out of the hot gas as it condenses into a mixture of water, carbonic acid (formed from carbon dioxide resulting from combustion) and other exhaust. The condensate drips out of the exchanger, and remaining gases – at only around 100 degrees – exhaust outdoors through plastic pipe. The heated air passes along ductwork and out into your home.

Condensate drains into a floor drain through a tube, which must be kept clear and free of bends or kinks. If condensate stays in the furnace, it will eat holes through metal, ruining your condensing gas furnace.

Other differences between conventional and high-efficiency condensing gas furnaces:

  • The gas valve – generally a two-stage burner gas valve with electronic controls
  • Electronic ignition
  • A sealed combustion chamber with its own air intake – pure air for combustion, and safer

To learn more about the great energy savings you can achieve for your Portland area home with a condensing gas furnace, please contact us at Roth Heating & Cooling.

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