What is the big difference between 80% efficiency and 90+ efficiency furnaces?
Most manufacturers build furnaces in two general configurations, 80% (non-condensing) and 90+% (condensing) efficiency. The 80% efficiency standard is the minimum federal standard for residential heating equipment. Flue gasses contain many compounds such as carbon dioxide, carbon monoxide, sulfuric and nitric acids. What the flue gas has the most of, though, is water in the form of steam. The 80% efficiency furnace is designed to prevent condensation when it is properly installed. Most furnace systems are common vented with the home’s water heater. Most water heaters are non-condensing under normal conditions. When common venting is required or when the existing metal venting is to be reused, the 80% configuration is most commonly used. Condensing furnaces (90%+ efficiency) extract almost all of the heat from the exhaust. As more heat is removed from the flue gasses, the products of combustion are cooled to the point that condensation occurs. The condensate is caustic to untreated meta
