A condensing furnace recovers heat that standard furnaces lose. While the gas-fired furnace has a long track record for reliability and lower operating costs, the standard model with only a single heat exchanger has always had one drawback: Valuable heat that could be utilized to warm your home more efficiently is lost during the combustion process.
Where does the lost heat go?
Most of the heat loss in a standard furnace goes up the exhaust duct in the form of water vapor contained in hot combustion gases. A condensing furnace, however, incorporates a secondary heat exchanger to capture heat from combustion gases before they are exhausted into outdoor air. As this extra heat is extracted, the hot gases cool and water vapor condenses. Thus, the designation “condensing furnace.”
What happens next?
The secondary heat exchanger adds the additional extracted heat to the system airflow to augment the heat produced by the primary heat exchanger. Condensation produced by the secondary exchanger flows down a drain line usually connected to the household drain system.
How are condensing furnaces better?
A condensing model provides several benefits over the standard gas-fired model:
- More heat from fuel consumed. Because heat that would normally be lost in a conventional furnace is conserved, heating performance is improved in a condensing model.
- Improved efficiency. Furnace heat efficiency is expressed by the AFUE (Annual Fuel Utilization Efficiency) rating. A higher AFUE indicates a more energy-efficient furnace. Standard gas-fired furnaces deliver AFUE ratings that average around 80. Condensing furnaces, however, provide AFUE of at least 90, with the highest-efficiency models exceeding 95%. As efficiency rises, monthly heating costs drop.
- Sealed combustion. A standard gas furnace incorporates an open combustion chamber that draws air for the combustion process from inside the house. A condensing unit incorporates sealed combustion that draws air from the outdoors through a plastic intake pipe. This avoids consuming indoor air that has already been heated for combustion, plus reduces the potential danger of backdrafting where toxic combustion fumes may enter the house.
For more about the benefits of a condensing furnace, contact Arpi’s Industries.
Our goal is to help educate our customers in Calgary, Alberta about energy and home comfort issues (specific to HVAC systems). For more information about other HVAC topics, download our free Home Comfort Guide.
Credit/Copyright Attribution: “iStock”
