The primary type of oil used in fuel boilers is fuel oil. This type of oil, also known as heating oil, is a refined byproduct of crude oil and is commonly used for heating purposes in residential, commercial, and industrial settings. Fuel oil is preferred for boilers due to its high energy content and ability to maintain a consistent flame, which is crucial for efficient heat generation.

Fuel oil is chosen for boilers because it offers several advantages. Firstly, it has a high energy density, meaning it can produce a significant amount of heat per unit of fuel. This is particularly important for large-scale heating systems, such as those found in industrial applications or large commercial buildings. According to the U.S. Energy Information Administration (EIA), the energy content of fuel oil is approximately 138,690 British Thermal Units (BTUs) per gallon, making it a highly efficient choice for heating.

Secondly, fuel oil is readily available and widely distributed across the United States. This ensures a consistent supply and reduces the risk of supply chain disruptions. Additionally, fuel oil is compatible with a wide range of boiler types, including oil-fired boilers, which are commonly used in colder climates due to their ability to provide reliable heat.

Furthermore, fuel oil is less prone to freezing than other types of fuel, such as natural gas, which can become difficult to handle in colder temperatures. This makes it a practical choice for areas with extreme weather conditions. The EIA reports that approximately 6.5 million households in the United States rely on fuel oil for heating, highlighting its widespread use.

In conclusion, fuel oil is the preferred choice for fuel boilers due to its high energy content, widespread availability, and compatibility with various boiler types. Its ability to maintain a consistent flame and provide reliable heat makes it an efficient and practical option for a wide range of heating applications in the United States.