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The red dye _only_ signifies that no road tax was paid on the fuel. That is the _only_ difference.
Depending on how cold it is at the time of purchase, diesel fuel or heating oil can be any particular blend of #2 fuel, #1 fuel, and some lubricating conditioners for engines. Most of the time all are the same thing, heating or diesel fuel, if about equal amounts of fuel & heat are used in your area. Suppliers don't like storing & selling 2 different things, costs more than just making a multi purpose batch. Any of these can be used for heating, likely your diesel engine will be ok with bits of heating oil tho a steady diet of the (rare) poorer formulations can cause problems over time.
However, the RED does not help you identify _any_ of this - it is only a tax issue, has nothing to do with the quality or type of fuel.
Most of the time, off road & heating oil is the same thing.
--->Paul )</font>
There are TWO agencies requiring dye to be put in diesel fuel, thus signifying that it is unusable as road fuel:
1. The IRS wants red dye in it if no tax has been paid, regardless of sulfur content.
2. The EPA wants red dye in it if there is more than 500ppm sulfur in it, which will soon change to 15ppm. I believe the color of the dye is going to change as well.