What volume of flue gas is produced by a 60,000 BTU/H Category I fan-assisted natural gas furnace operating at 50% excess air?

To determine the volume of flue gas produced by a 60,000 BTU/H Category I fan-assisted natural gas furnace operating at 50% excess air, one must consider the combustion process, which typically includes natural gas reacting with oxygen to produce carbon dioxide and water vapor as byproducts.

For natural gas, the combustion process can be summarized as follows: When one cubic foot of natural gas combusts completely with the proper air-fuel mix, it requires a certain amount of air. The stoichiometric combustion of natural gas (considered mainly methane) generates approximately 10 cubic feet of flue gas for every cubic foot of natural gas burned. This number varies based on the excess air ratio.

When operating with 50% excess air, the total amount of air used becomes about 1.5 times the stoichiometric requirement. Therefore, for every 1 cubic foot of natural gas combusted, the total volume of flue gas produced increases.

For a furnace rated at 60,000 BTU/hour, you need to determine how much gas is being consumed. The average energy content of natural gas is around 1,000 BTU per cubic foot. So, the furnace would require 60 cubic feet of natural gas per