Both butane and propane are Liquefied Petroleum Gases (LPGs) that serve as popular, clean-burning fuels for a variety of heating and cooking applications. They are hydrocarbon compounds derived from natural gas processing and crude oil refining, making them similar in origin and general function. While they share the “ane” suffix, their distinct chemical structures lead to significant differences in practical use, especially concerning performance in varying temperatures. The choice between them ultimately depends on the intended application and the environmental conditions where the fuel will be used.
Molecular Composition
The fundamental differences between the two fuels begin at the molecular level. Propane has the chemical formula C\(_{3}\)H\(_{8}\), meaning each molecule contains three carbon atoms and eight hydrogen atoms. Butane is slightly larger, with a formula of C\(_{4}\)H\(_{10}\), containing four carbon atoms and ten hydrogen atoms. This single extra carbon atom makes butane a heavier molecule than propane.
The difference in molecular weight impacts how much fuel can be stored and how the fuel behaves under pressure. Butane’s larger structure makes it denser than propane. This molecular distinction is the reason for the practical variations in boiling points, energy content, and storage requirements.
Temperature Sensitivity and Usability
The most crucial practical distinction between the two gases is their boiling point, which dictates their performance in cold weather. The boiling point is the temperature at which the liquid fuel turns into usable gas vapor. Propane’s boiling point is exceptionally low, around -44°F (-42°C).
This low boiling point means propane will continue to vaporize efficiently and supply gas to an appliance even in extremely cold conditions. Butane, by contrast, has a significantly higher boiling point, typically around 31°F (0°C). When the ambient temperature drops below this point, butane remains liquid, and the appliance will fail to operate.
Propane is the reliable choice for year-round outdoor use in any climate, including home heating. Butane is generally limited to warmer climates or indoor applications where the temperature is consistently above freezing.
Energy Output and Common Uses
When comparing energy content, the results vary depending on how the fuel is measured. Butane has a slightly higher energy density by volume than propane. A gallon of liquid butane yields approximately 102,000 BTUs, compared to about 91,000 BTUs for liquid propane. This makes butane slightly more efficient for applications where space and volume are a concern.
Propane, however, has a slightly higher energy content by weight. Because of its ability to function in all weather conditions, propane is the standard fuel for large-scale uses like whole-home heating, large outdoor grilling, and powering vehicles. Butane is favored for highly portable, small-volume applications, such as disposable lighter cartridges, small camping stoves, and indoor heating appliances.
Handling and Storage Requirements
The physical requirements for storing each gas differ significantly due to their respective vapor pressures. Because propane has a much lower boiling point, it must be stored under higher pressure to keep it liquid. At 59°F (15°C), propane is stored at approximately 7 bar (about 100 psi). This high pressure necessitates the use of heavy, thick-walled steel tanks designed to withstand the stress, making propane tanks large and robust.
Butane only requires a fraction of that pressure to remain liquid, around 1.5 bar (about 22 psi) at the same temperature. This lower pressure requirement allows butane to be stored in much lighter, thinner, and less expensive containers, such as the small, disposable cartridges common for camping and portable heaters. Butane is also generally cheaper to purchase than propane.