Propane Vs Natural Gas Usage

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Residences that use gas for cooking and heating commonly use either natural gas or propane. Which gas they use depends on the local infrastructure. If the infrastructure is available natural gas is both convenient and typically cheaper than propane. When the systems for direct access are not available, i.e. outside of municipalities, then the choice is propane. The components in natural gas include other hydrocarbons such as methane, butane, and propane too. A hydrocarbon is a molecule composed of only carbon and hydrogen atoms. As you can see in the table the names of each molecule are based on the number of atoms. What we call natural gas is actually a mixture of hydrocarbons.

 

Gas

Formula

% In Natural Gas

Methane CH4 70-90
Ethane C2H8 0-20
Propane C3H8 0-20
Butane C4H10 0-8
Other Varies 0-5

 

Gases are heavily influenced by temperature and pressure. Propane is a gas at room temperature because its boiling temperature is at -44°F, whereas natural gas boils at -258°F in comparison. When a consumer buys propane in common LP tanks it’s in a liquid form, this is caused by pressure. By increasing pressure propane becomes a liquid because the vapor pressure within the tank is too intense for the liquid to boil. The gas occupies the headspace, and is typically no less than 20% of the total volume. As this vapor is released the temperature in the tank drops allowing the compressed liquid to expand and change to a gas, this process is called a phase change. Propane due to its higher boiling temperature does not need to be under as much pressure as natural gas to keep it in liquid form. Natural gas requires much greater pressures and intensive piping/distribution systems in order to maintain delivery pressures, making natural gas systems outside of municipalities expensive and difficult to maintain. Most consumers are not provided a choice since one system or the other is in place and is maximized for the highest efficiency.

 

Combustible gases have properties which differentiate them on both a physical and chemical level, such as flame temperature, densities, and Btu’s produced. This last category is essential to consumers since it determines how much gas is consumed. If both gases are burned at the same rate to heat the same amount of space, natural gas will use 2.4 times as much gas as propane will. If a 100,000 BTU/hr furnace uses 97 cubic feet of natural gas (100,000 ÷ 1,030 = 97.1) in one hour then the same furnace will use about 40 cubic feet of propane (100,000 ÷ 2516 = 39.7). Although it seems unlikely that consumers would use natural gas, based on its lower energy potential, it has other characteristics that are valuable.

 

Natural gas from an environmental aspect burns “cleaner” than propane and it’s lighter than air making ventilation easier. Propane although heavier than air produces more heat with less gas consumption, also it is easier to store since it is a liquid at lower pressures.