A condensing gas furnace recovers energy normally lost by conventional furnaces. In the standard forced-air gas furnace, some of the heat energy produced by burning natural gas goes up the exhaust vent with hot combustion gases. That’s the reason standard gas furnaces have always been limited to an AFUE (annual fuel utilization efficiency) rating below 90 percent. A condensing gas furnace incorporates an extra heat exchanger to extract heat released when combustion gases condense. Condensing models break through that efficiency ceiling and offer AFUE ratings of 90-98 percent. However, efficiency ratings, household comfort and even safety assume an installation performed according to industry standards. Here’s what to watch for in the installation of a condensing furnace:
- Installation should be preceded by a professional sizing calculation to ensure the BTU output of the furnace
matches the heating requirements and thermal characteristics of the house. Oversized and undersized furnaces are a liability in terms of efficiency, comfort and expected service life. - Make sure a sealed combustion furnace incorporates an intake pipe properly routed to the exterior of the home – either through the roof or an exterior wall – to supply outdoor air for safe combustion and maximum efficiency. Alternative air intake pipes that utilize indoor air from other parts of the structure can still backdraft hazardous combustion fumes into the house.
- The furnace exhaust pipe must be sized per manufacturer’s recommendations according to the unit’s BTU output. If the exhaust pipe is routed through an exterior wall, it should slope back toward the furnace in order to drain condensate backwards into the condensate trap and drain. The exhaust pipe should terminate outdoors immediately next to the intake pipe to ensure that wind pressure is equal in both pipes.
- The furnace unit should be installed slightly tipped in the proper direction to drain condensate out of the collector and into the drain line that connects to a household drain.
Serving the Twin Cities since 1974, Marsh Heating & Air Conditioning offers professional installation of heating systems such as the high-efficiency condensing gas furnace. Contact us today for more information.
Our goal is to help educate our customers in Minneapolis-St. Paul, Minnesota 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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