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Condensing Furnaces: How They Differ From Conventional Units

Condensing Furnaces: How They Differ From Conventional UnitsYou’ve probably heard of condensing furnaces, but aren’t entirely sure how they work. First, though, here’s a refresher on how a conventional old-style gas furnace works: airflow is drawn in through the cold air return and air filter, and then into the circulating fan. Heat from the gas burner flows into the heat exchanger, heating the surrounding air before it’s circulated throughout the house via the ductwork. Combustion gases generated by the burner are vented out of the home through the flue.

Believe it or not, there’s still plenty of heat to be found within those combustion gases, and it all goes to waste as it travels up the flue. A condensing furnace puts an end to that by extracting as much useful heat from combustion gases as possible, offering impressive energy efficiency in the process.

The condensing furnace’s primary heat exchanger operates similarly to a conventional unit, removing the bulk of the heat from the flue gases generated by the gas burner. Afterward, a secondary heat exchanger takes the resulting exhaust gases and recirculates it through a series of small tubes. As the device continues to extract heat, the gases eventually cool down and condense into carbonic acid, a combination of water and carbon dioxide. To better resist the resulting corrosion, the secondary heat exchanger is made of high-quality stainless steel.

In an airtight home with very few leaks, conventional systems can accidentally draw (or “back-draft”) exhaust gases from the chimney into the home as it attempts to draw in fresh air. Fortunately, the exhaust from a condensing furnace is cool enough that it can be vented via a plastic flue gas vent through a home’s sidewall, instead of out the rooftop chimney. The carbonic acid eventually exits into a floor drain via PVC piping.

Condensing furnaces offer AFUE ratings starting at 90 percent, with many units capable of 96 percent AFUE or better. In comparison, a standard natural gas furnace seldom rises above 80 percent AFUE.

Like tankless water heaters and high-efficiency insulation, a condensing furnace can help save you plenty of money over the long run. At Donald P. Dick Air Conditioning, we can show you how Fresno area residents are saving energy and money, thanks to our courteous and professional services.

Our goal is to help educate our customers in the greater Fresno, California area about energy and home comfort issues (specific to HVAC systems).  For more information about condensing furnaces and other HVAC topics, download our free Home Comfort Resource guide.

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