Which gas's heating value is subject to variability based on its constituents?

Natural gas is composed primarily of methane, but its exact composition can vary significantly depending on the source from which it is extracted. This variation in chemical makeup affects its heating value. Natural gas may contain other hydrocarbons, carbon dioxide, nitrogen, and varying amounts of higher hydrocarbons, which can influence how much energy it produces when combusted.

Due to this fluctuating composition, the specific energy content (heating value) of natural gas can change, making it distinct from gases like hydrogen, propane, or butane, which typically have clearer and more consistent heating values. Hydrogen has a high heating value, but it is a pure element, thus less variable. Propane and butane are also more consistent in their compositions and heating values compared to natural gas. This characteristic of natural gas underscores the necessity for accurate measurement and analysis in applications where energy content is critical.