Kerosene is a thin oil distilled from shale or petroleum. It has many uses, including as a fuel, solvent, and thinner. There are two basic types of kerosene. Type 1-K and type 2-K kerosene are distinguished by the difference in sulfur content.
Type 1-K Kerosene
Type 1-K kerosene contains 0.04 percent sulfur by weight. This is primarily used for all kerosene heaters and is the approved and recommended fuel by the National Kerosene Heater Association. This type of kerosene is widely known as being refined enough to safely use with indoor heaters. Though cleaner than the 2-K type of kerosene, type 1-K still may emit harmful odors or vapors that can cause nausea. This type of kerosene can also be a bit difficult to find.
Type 2-K Kerosene
Type 2-K contains 0.30 percent sulfur by weight. The high sulfur content tends to adversely affect the wicking ability of the kerosene. This causes the need for frequent maintenance and cleaning if used in a kerosene heater. If you don't perform maintenance often, the buildup of sulfur dioxide emissions can lead to fire or explosion. Type 2-K is known to emit more of a sulfurous odor, due to the higher concentration of sulfur in the fuel.
Type 1-K and type 2-K kerosene cannot be distinguished by a visual inspection. If you're unsure which type of fuel you have, don't use it in a kerosene heater. Some dealers mistakenly believe that if the kerosene is clear, then it must be type 1-K. However, color and clarity can vary in a particular grade of kerosene. This has to do more with the refining process than the content. Color dyes also may be added during the manufacturing process to distinguish it.
When buying from a retailer, look for a specific mark identifying the type of kerosene. If the fuel type is unmarked, always assume that you're working with 2-K kerosene and exercise extra caution. Type 2-K can cause a buildup on the wick and internal components of the heater that may lead to a fire hazard. Also, extra ventilation is needed if operating a heater with type 2-K kerosene.