Why is that a “best system”? You could get stuck with a big final payment. Most people would not want that, would not pay attention and then get a nasty surprise.
———-
You track month to month usage. No more extremely high bills in the German heating or cooling system.
And a large final bill? Most of it goes into the next year’s billing average. Maybe 100 to 200 € tops. Most I paid was €60 extra
Season should be system
Many heating oil companies offer something like that.
But if there is no final payment paid at the end, that sounds more like a rolling averaging system.