What are the complete combustion by-products of natural gas?

The complete combustion by-products of natural gas primarily include carbon dioxide and water vapor. When natural gas, which is primarily composed of methane (CH4), is burned in a sufficiently oxygen-rich environment, it reacts completely to produce these by-products.

Carbon dioxide is a naturally occurring gas that is a part of the Earth's atmosphere and is also used by plants during photosynthesis. Water vapor, on the other hand, is a standard by-product of combustion that exists in the air and naturally in the environment.

Both carbon dioxide and water vapor are non-toxic to humans at typical atmospheric levels. While carbon dioxide can pose risks in very high concentrations—such as in poorly ventilated spaces—under normal conditions, it is not considered toxic. This makes the correct characterization of these combustion by-products as non-toxic.