I'm heating an 1840's, 3,000sqft farmhouse and DHW with so, so insulation (Improvements as money permits) decent windows, good doors, etc... with a Central Boiler E-Classic 1400.  I live in the Upper Valley region of NH (near Dartmouth College).  When the temps are around 20 degrees +, 1/2 a firebox load will go about 12 hours.  When it's colder than that coupled with wind, the firebox will be about 2/3's full to go 12 hours.  The only time i ever filled the firebox completely full is the first winter I owned it (this is my 3rd season with it).  The temps were in the 20's, calm winds and it went nearly 30 hours.  However, I'm somewhat of a control freak and need to know that things are running properly, so I tend to it every 12 hours.  I've gone through a bit more wood this year than I did last year at this time due it being a colder than normal December.  My best guess is I've gone through about 1 and 3/4 cord of wood since a week before Thanksgiving.  My house is at 70 degrees, 24/7.  I tried it at 72/73 degrees, but those temps are too warm for me.  Roger