CharlesDavis:
The gas nozzle should deliver a fixed mass of gas per unit time .... Kg/Hr or pounds per hour. If you could find that specification, then integrating the gas valve open time would give a reasonably accurate consumption.
My oil burner has an orifice and creates pressure. the orifice is listed at gallons per hour at x pressure. I believe that a gas furnace works in the same way.
what I did was to run the data logger.
when I got a fill, the receipt had time and day.
on the next fill, I just too, the spreadsheet from my data logger and totaled the run time.
simple math at that point and the data is a few percent off from actual. and that might be dependent on the guy filling the tank. one guy can put in 5 gallons more or less than the next.