What is number 2 heating oil?
NO.2 Heating Oil is sometimes abbreviated as (HHO) Also Known As Fuel Oil, Furnace oil, #2 fuel oil and many others. Heating oil is used to run heating systems The chemical makeup of NO.2 Heating Oil is made from petroleum and from that hydrocarbons are made. Hydrocarbons, to put it very simply, are a mixture of hydrogen and carbon. Heating oil can be very chemically similar to diesel fuel, so much so it can be used to serve each other’s purpose. So theoretically if you ran out of heating oil you could use diesel fuel instead. Diesel fuel will work since the two fuels are so similar.
Sources: Wikipedia: Heating oil – https://en.wikipedia.org/wiki/Heating_oil