How many grades of fuel oil are normally considered as heating oils?

In the U.S., three grades of fuel oil used for heating are generally recognized. The grades are No. 1, No. 2, and No. 4. No. 1 heating oil is more highly refined than No. 2, and is less viscous. For this reason, it is more suitable for outdoor storage in very cold climates.

No because if you do the higher number minus the lower number you will get a positive. if you do it the other way around you will get a negative number

Idrk but i think u should figure out the n dia n then the units it will make it way more easier