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High-Efficiency Condensing Gas Furnaces: The Basics

Posted on March 7, 2013

Condensing gas furnaces look and in many ways act just like conventional furnaces. Like conventional systems, a condensing gas furnace takes in air through a cold air return system, passes it through an air filter, moves it with a circulating fan and heats it with a gas burner.  Heat is then extracted within the condensing unit – and this is where condensing gas furnaces are far superior to their older counterparts.

Unlike conventional systems, the condensing unit in condensing gas furnaces has not one but two heat exchangers – one for primary heat exchange, the other to exchange condensed exhaust gases. This additional exchanger ensures that maximum heat is extracted from the process, for far superior efficiency.

Furnace efficiency is measured by annual fuel utilization efficiency. AFUE is the ratio of heat output in relation to the energy consumed. According to the U.S. Department of Energy, a high-efficiency system offers from 90 percent to more than 98 percent AFUE, compared to conventional systems that are below 85 percent – even below 56 percent in units more than 10 years old.

While the heat exchangers are what sets high-efficiency units apart, other optional components provide greater efficiency, too – such as variable speed blower motors. These are quieter, require less maintenance and are up to 60 percent more efficient than the standard split-capacitor motor found in older systems.

Condensing gas furnaces commonly have multiple gas valves or dual-stage burners to allow for different flame settings, and ECM controls to modulate the burner and blower. Unlike conventional furnaces, blower compartments are usually insulated. The combustion chamber is sealed, so it doesn’t use air that has already been heated.

Condensing gas furnaces use a PVC pipe that empties into a floor drain to discharge condensation. The exhaust is cooler than a standard furnace, so it can be vented with a plastic pipe through a side wall or roof instead of a chimney vent.

There are many options to choose from in a condensing gas furnace. Contact us at Comfort Systems in Wichita to help go over the different components, prices and options to find one that meets your needs.

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

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