Arkansas HVACR NewsMagazine January 2020

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COMBUSTION AIR In order to maintain combustion (burning) you need three things, fuel, heat and oxygen. If you have all three in the proper proportion you can maintain a continuous state of combustion. Remove one (or reduce one sufficiently) and the triangle of combustion can collapse. In a common NG gas furnace the heat is the igniter, the fuel is Natural Gas and the oxygen is provided by combustion air. Combustion air is literally just the air needed to provide a continuous supply of air for proper combustion (burning). In the case of burning fuels like natural gas our goal is to achieve complete combustion where the end products being vented are CO2 and H2O and this requires the right mix of air and fuel. You may note that we are featuring 3 articles related to gas appliances by Bryan Orr. A synergistic trilogy of safety, efficiency, and efficacy. Wow! That is a mouth full. Hope you enjoy and are benefited by Bryan’s expertise. We appreciate his contributions and suggest that you sign up for his podcast by clicking on this box. Tis is the season for warm homes and hearts. Welcome to the HVACR NewsMagazine. Bryan Orr , HVACR School.com

For perfect combustion you need about a 10:1 ratio of air to fuel with safe levels of extra air or “excess air” putting us more into the 13.5:1 to 15:1 range. All gas fired appliances must have both a flue / chimney to exhaust the leftover products of combustion (outlet) as well as combustion air to provide the oxygen for burning (inlet). In high efficiency furnaces the combustion air is generally piped in, directly from the outside straight into the combustion chamber. This creates a dedicated source of oxygen and also a cleaner install as no other provisions need to be make for combustion air. In 80% furnaces the burners usually have “open” combustion and they rely on air being drawn into louvers on the furnace cabinet. In this design the space on which the furnace resides must have open communication to the outdoors or other “uncontained” space. The International Fuel Gas Code requires the following combustion air