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How is the percentage of CO2 in the flue gases of a natural gas furnace an indicator of combustion efficiency?

  1. Higher CO2 percentage indicates better combustion

  2. Lower CO2 percentage indicates better combustion

  3. CO2 percentage does not indicate combustion efficiency

  4. Stable CO2 percentage indicates better combustion

The correct answer is: Higher CO2 percentage indicates better combustion

The correct answer is A. A higher CO2 percentage in the flue gases of a natural gas furnace indicates better combustion efficiency. This is because when combustion is efficient, more carbon in the fuel (natural gas) is converted into carbon dioxide (CO2) rather than other byproducts like carbon monoxide or soot. Therefore, a higher percentage of CO2 in the flue gases suggests that the fuel is being burned more completely, which is a good indicator of efficient combustion in a gas furnace.