Your dad is doing great on consumption. Most homes are getting a fill every 4-5 weeks. I have been in the heating oil industry for 25 years,including as VP of ops for a very large dealer in Boston and now working with 600+ companies across the country. Feel free to reach out if you want to discuss further.

Mine was filled 12/24. Now down to half in a 2500 sf home, fairly new.

Lot of glass is uncovered at night is cooling the house.

275 gals in 9 weeks.... Not surprised they ran out. Apparently not on autofill.

Dont forget that depending on the age of the tank, there will be sludge at the bottom of the tank. Upwarda of 25 gallons.

How long has your dad owned the house? Can he look back and see what the usage was in prior years.

I use 600 to 800 a year for my 1960sq ft forced hot air home.

275g (actually closer to 260 due to headspace allotment) over 2.5 months is pretty typical in my opinion.

*edited as my math was a bit off