If you’re heating with oil today, you should find out from your oil company how much oil you use during the heating season.  Use the average of 3 years to reduce the chance of one unusual winter throwing off the estimate.  Take your average consumption and divide by 116.  That should get you to a good approximation of your pellet consumption.

If you’re heating with propane, your calculation will be slightly different because propane contains less energy per gallon than does heating oil.  For propane, divide your consumption in gallons by 175.

For example, 1000 gallons of heating oil = 1000/116 = 8.6 tons wood pellets, and 1000 gallons of propane = 1000/175 = 5.7 tons of wood pellets.