Copyright Goodheart-Willcox Co., Inc. Chapter 3 Boilers 43 3.2 Types of Fuel The earliest manufactured boilers burned either coal or wood, Figure 3-3. With the exception of outdoor wood boil- ers (discussed in Chapter 20, Outdoor Wood Boilers), most of today’s boilers utilize fuel oil, natural gas, propane (LP), or electricity as a source of fuel. 3.2.1 Fuel Oil Fuel oil is considered a fossil fuel, as it is derived from crude oil through distillation. There are six grades of fuel oil, with the lightest grade being #1 and the heaviest being #6. The fuel oil grade most often used in residential and light com- mercial boilers is #2. This fuel oil is the same fuel used in automotive vehicles that run on diesel. Fuel oil has a heating value of 140,000 Btu/gallon. Although the demand for fuel oil for boilers has reduced somewhat in the upper Midwest region of the United States due to the increased popularity of propane fuel, it is still quite popular along the Northern Atlantic states and up into New England. Fuel oil is delivered by tanker truck to homes and businesses, where it is stored in tanks either above ground or below, Figure 3-4. This is covered in greater detail in Chapter 5, Oil Systems. 3.2.2 Natural Gas Natural gas results from the decay of organic material from plants and animals over millions of years, forming deep pockets within the Earth’s surface. Natural gas is primarily comprised of methane (CH4), but it can also contain small quantities of ethane, propane, and butane. All of these gases are classified as hydrocarbons, which are combustible, efficient, clean-burning gases. In its native state, natural gas is odorless and colorless. Gas utility companies add sulfur compounds, called odorants, to natural gas to make gas leaks more easily detect- able. The energy content of natural gas is approximately 1050 Btu/cubic foot. Natural gas is distributed across the United States by a network of pipelines, Figure 3-5, and delivered to homes and businesses through underground piping. 3.2.3 Liquefied Petroleum (LP) Propane is the most common type of liquefied petroleum (LP) gas and can include a mixture of butane and propane. Propane has a heating content of SAFETY FIRST Boiler Operator License Local, state, and federal agencies require employees and technicians to obtain a boiler operator’s license in order to operate larger boilers. This license typically applies to commercial boilers and boilers located in public and municipal buildings. Only those employees and technicians who hold the appropriate license may operate or repair any such boiler. Smaller boilers designed for residential or light commercial use are typically exempt. nata-lunata/Shutterstock.com Figure 3-3. Many original boilers were coal fired. Marcel Derweduwen/Shutterstock.com Figure 3-4. Fuel oil is stored in tanks either above or below ground, where it is piped to the boiler.