Averaging 900 gals per yr. at 70,what would I expect at 71?{oil fired hot water sys.}

It will depend on the outside temperature this year. To compute average daily consumption, you would need to tell me the average outside daily temperature for the days your boiler ran and the number of days it ran.

Not only calculate the average temp. but the average wind mph. and how many times you open the front door each day.What I'm getting at you have a lot more variables of day to day living that can change your bill than the 1 degree swing on the thermostat.