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Propane and butane are two similar gases used for heating and other fuel applications. Although proponents of each gas hold theirs to be the superior, both have benefits and disadvantages. Butane burns more cleanly and provides more energy, but propane is a better choice for situations in which temperatures may drop below freezing. Ultimately, the gases are quite similar, and the choice between the two largely depends on the availability and intended use of the product.
Both gases are derived from petroleum, either from oil or natural gas, but have different chemical structures. Each burns at similar temperatures and both release water and carbon dioxide as waste products. If the amount of oxygen available is limited when the gasses are being burned, they may also produce soot and carbon monoxide. In some cases, the gases may be used interchangeably, but people should always consult the manufacturer before attempting to substitute one for the other.
The fire and hazard risks of both gases are quite similar. In North America, the gases are represented in the National Fire Protection Association (NFPA-704) classification system identically. The rating indicates high flammability, normal stability, a mild health hazard risk, and no special considerations such as an unusual reaction when mixed with water.
Characteristics of Propane
Propane is used in North America as fuel for heating houses, and is also available in smaller portable tanks. Gas barbecues, camping stoves, and lanterns frequently can be used with propane fuel. Mixed with small amounts of other substances like butylene, propylene, and butane, it can be used as an automobile fuel known as liquefied petroleum gas (LPG). The odorless gas will often have ethanethiol, which has a strong odor, added to it so any leaks can be more easily detected.
If the gas needs to be stored for a long time or in variable weather conditions, propane is usually a better choice than butane. It is relatively easy to liquefy and compress, and has a boiling point of -44°F (-42°C), which means that it turns into a gas as soon as it comes out of the tank at any temperature above this. Propane can easily be stored outside in almost all environments, since temperatures below freezing don't affect how it is stored or used.
Characteristics of Butane
Butane, while not as easy to find in many places, is nonetheless a popular fuel for lighters, torches, and some camping stoves. Aerosols may also use the gas as a propellant. Although butane is generally less expensive than propane, it can be also be more difficult to use; because it is not as common, many devices are not designed to work with butane tanks.
This gas also has a boiling point right around freezing — 32°F (0°C) — so it does not work well at very low temperatures. Below its boiling point, butane stays a liquid, and there is no pressure change to force it out of its container. Butane is rarely used to heat homes or buildings in places where it gets very cold because it cannot be stored outside and still work effectively.
One of the advantages of butane is its improved fuel efficiency. If similar volumes of both substances are burned at temperatures above freezing, butane will provide about 12% more energy. This advantage makes butane a good choice for those trying to pack light, such as backpackers or campers. As long as access to an adequate supply is available, the energy efficiency and price advantage can make butane a better deal in many, but not all, circumstances.
Propane and butane are often combined in mixed fuels, which provide some of the advantages of each. Such mixes are popular for camping stoves in particular. Because propane has a lower boiling point, it can be used to force the butane out of the container, even at temperatures at or below freezing. Pure propane needs a strong steel container to hold it under pressure; combining it with butane means that the pressure can be lower, and the container lighter, which is important for campers and backpackers.