Oil-fired boilers burn heating oil to generate heat, which is then used to warm up water. Some boilers convert water into steam that is spread throughout pipes, while others use pumps to send the hot water through the pipes. Heat is then radiated through the structure.
Oil-fired boilers are almost always closed units with water that should be replaced on occasion for maintenance purposes. These systems do not require a constant connection to a water line while in use. Compared to fireplaces, furnaces and space heaters, boilers operate at high efficiency levels and can use most of the energy stored in heating oil.
Steam boilers were once the most common type of boiler due to their easy use. Steam flows through pipes automatically, while hot-water boilers require pumps. However, the high operating temperature of steam boilers makes them inherently less efficient, so hot-water boilers are generally preferred.
Natural gas boilers operate at slightly better efficiency levels, and the significantly lower cost of natural gas makes them the most popular boiler types. However, heating oil is still used due to its easier and safer storage options. In regions of the country where gas lines are unavailable, homeowners often prefer storing heating oil containers over storing natural gas bottles.