Since we lost our heat-pump hot water heater, we've been burning oil to make hot water.
The burn runs are done on demand "Google, turn on hot water" when we have extra demand.
But, normally it's on a timer, and runs (15 to 20 min) in the morning (before work) and in the evening just before we get home.
On the weekends, it's 3 runs, morning, noon and evening.
If the boiler hits the high cutoff temp, it run time is less.
The new water mixer has less heat loss. (2 check-valves) A bit of savings.
At a burn rate of 1-gal per hour, It's typically less than 3/4 of a gallon per day.
So, a 275 gallon tank of heating oil lasts us about 1 year.
So far the really cold nights haven't really used a lot of extra oil.
The new mini-split works okay when it's extra cold.
The old Sanyo still works down to 5 to 8 degs depending on the dewpoint.