Liquefied Petroleum Gas

Liquefied petroleum (LP) gas is a hydrocarbon mixture extracted primarily from wet natural gas and sold commercially as propane, butane, bottled gas, or under a variety of different brand names. The terms dry and wet natural gas refer to the gasoline content per 1000 ft3. Natural gas is regarded as dry if it contains less than 0.1 gallon of gasoline per 1000 ft3. and wet if it contains more than 0.1 gallon.

Propane is used extensively for domestic heating purposes. It contains 2516 Btu/ft3 (91,547 Btu per gallon), or about two and a half times the Btu content of methane (natural gas). Table 5-2 compares the typical properties of propane and butane. Unlike natural gas, propane is heavier than air. An undetected leak can be quite dangerous because the escaping gas will accumulate in layers at floor level. An explosion can be set off if the gas reaches the level of the pilot flame in the furnace.

Table 5-2

Typical Properties of LP Gas




Btu per ft3 60°F



Btu per lb



Btu per gal



Ft3 per lb



Ft3 per gal



Lb per gal



Courtesy National LP-Gas Association

Propane is frequently delivered in bulk and stored in large, sta­tionary tanks holding from 100 to 1000 gallons. It is then piped into the home or building in much the same manner as natural gas. For small usage (e. g., trailers or homes that use only enough gas for one or two appliances), the LP gas is delivered to 5- to 25-gallon cylinders. The suggested clearances for LP gas cylinders and storage tanks are shown in Figure 5-1. The size of the storage tank required by an installation depends upon the weather zone in which it is located. Recommend tank sizes for the various weather zones in the United States are given in Figure 5-2.

Posted in Audel HVAC Fundamentals Volume 1 Heating Systems, Furnaces, and Boilers