It only works with any accuracy if you have the EXACT DATES of the meter readings, not the month. One week of Polar Vortex or unusually warm weather that fell outside the exact period of that fuel use can skew the results by quite a bit.
That said, unless you spent a month in Belize with the thermostat cranked back to 50F your heat load isn't very big. Assuming the meter gets read mid-month,
downloading base-65F HDD from weather station KMAREADI3 in nearby Reading MA and totaling the HDD from November 15 through March 14 (inclusive) it comes to 4479HDD, over which you used 809 therms in an 80% efficiency boiler, which means at most 0.8 x 809= 647.2 therms of heat was injected into the heating system.
That's 647.2/4479= 0.1445 therms per HDD
x 100,000 BTU/therm= 14,450 BTU/HDD
Divided by 24 hours in a day is 602 BTU per degree-hour as your constant.
The outside design temp in Wakefield is about +7F, which is 58F cooler than the presumptive 65F heating cooling balance point. The implied maximum 99% design heat load is then about
58F x 602 BTU per degree-hour= 34,916 BTU/hr.
As a sanity check, ~35,000 BTU/hr into ~2300' of living space is about 15 BTU/hr per foot of conditioned space, which is on the high side of normal for a 2x4 framed raised-ranch, but not outlandishly high. (That would be more typical at an outside design temp of 0F, not +7F, maybe 10% higher than I would expect, but still "in the range".) There are probably some cost-effective air sealing and spot insulation measures to be taken. If the upper floor is cantilevered it probably leaks air there, with a high likelihood of discontinuity in the insulation to boot.
If you assume that's the actual heat load (it's actually an upper bound, and without exact billing dates it could be off by 5% but not 10%) applying the ASHRAE 1.4x maximum oversizing, the biggest boiler you would be looking for would a DOE output in the range of (1.4 x 34,916 BTU/hr=) 48,882 BTU/hr
Among dumb-controls no frills cast iron beasts out there the
Burnham P202X fills the bill, as does the
Weil McLain CGi-3 (though the CGi 2.5 is probably a better bet if you can nail the load down with better accuracy) or the
SlantFin S-60. There are others.
With any of these boilers, if all zones are calling for heat at once, 50,000 BTU/hr into 180' of baseboard is about 280 BTU/hr per foot, which balances at a water temp of about 135F, so it's likely that the installer would have to install a bypass branch at the boiler to keep the EWT high enough to mitigate condensation risk. This is very standard stuff, but it's important to ask the contractor what approach they are going to take, if only to tip them off in case they don't usually do the napkin-math analysis. If you didn't mind the electronic controls, the
Burham ES23 is internally plumbed with cool return water protection down to 110F EWT, but it's 59K DOE output is more like 1.7X the output, and a bit more problematic for your zoning configuration:
Looking at your zones, the shortest are 24-25' long. 50,000 BTU/hr into 25' of baseboard is 2000 BTU/hr per running foot, which is 3x as much as the baseboard can actually deliver even with the boiler temp set to it's maximum. That's a recipe for short-cycling the boiler into lower efficiency & higher maintenance but it'll probably work, since most of the time you'd likely be having 2-3 zones calling at any one time if you right-size it. If you put anything BIGGER than a 50K boiler it becomes something of an efficiency disaster, unless it's an unusually high mass boiler. The Utica's 160,000 BTU/hr output into 25' of baseboard is exactly this sort of disaster, which means your real heat load is likely to be LOWER than the fuel use calc indicates.
Ideally the smallest/shortest zone would be at least 50' of baseboard, and 75' would be even better, since a 50K output boiler could even balance with the radiation output delivering a single burn, not cycling at all during a continuous call for heat from just one zone. Zoning it by floor rather than room-by-room micro-zones is usually better, but the baseboard in each room needs to be proportional to the calculated room loads for that to work without big temperature differences between rooms. (Again, a room by room Manual-J would be able to suss that out.)