I've been using right around 75#'s every 24hrs. Outside temp doesn't seem to matter much. If I crank up the stove, it will easily burn 100#'s, but won't last long. I like keep the heat steady for at least 12 hrs.
Started burning off & on in October, then steady by end of November. As of right now, I've burned 3.25 tons.
I used to use 3.75 tons for the entire season with the Mark I, but we had some pretty cold rooms & quite a bit of oil usage. Now the entire house from basement to second floor is 65* - 70*. Not sure of my exact square footage......realtor had one measurement (1400) & bank got another (1800), so I'll say 1,600 sq.ft.(not including basement) poorly insulated & drafty 150 yr. old house. It's looking like I may be short 1.5 tons this year, judging by my usage (first season with Mark III). Bought 5 tons this season & had 1/4 ton left over from last season, so it's looking like I'll need 6.5 tons to make it thru next season.
....And this is keeping the oil burner on too!
If I were to shut the oil off, I'd probably use 7.5 - 8 tons!