Reason that I brought up air-sealing and insulation is that several heating contractors are concerned that the
TT prestige trimax series 60 (input modulation of 16 to 60K MBH) would not be able to supply enough heat for the whole house.
And unless they did a careful fuel-use analysis on the previous system and an honest Manual-J or even an I=B=R spreadsheet calc, their opinions aren't worth the toilet-paper they wrote it on. Fear of undersizing is rampant amongst hacks, but rarely justifiable. The more reasonable fear should be of oversizing.
Air sealing is almost always cost-effective, as is fixing any gaps in the insulation, and those measures DO lower the heat load. But the notion that an 1800' house in Westchester needs more than 55,000BTU/hr of boiler output (that's 30 BTU/ft-hr!) is just nuts, unless there is literally no insulation in the walls, and all of the windows are single-pane, all of which would be necessary & cost-effective things to rectify on comfort grounds alone. Ratio rules of thumb are pretty lousy gauges of reality, but most 1920s homes won't run more than ~20 BTU/ft-hr , and will often be in the 15BTU/ft-hr range with a bit of air sealing and (usually absent) foundation insulation. At the more likely 20 BTU/ft-hr an 1800' house would only need 36,000 BTU/hr which is barely over the MINIMUM output of the -110.
As-zoned the -110 is guaranteed to short-cycle at condensing temps- you'd literally be better off with ~100KBTU/hr mid-efficiency cast iron boiler with smarter controls if you're hell-bent on installing a boiler that oversized. You only get the benefits of mod-con efficiency if it's actually modulating and condensing, which is why you HAVE to install the smallest one that actually meets the load, and have small zones of low-mass-low-emittance radiation like fin-tube.
Run a crude I=B=R spreadsheet on your house on a room-by-room basis. Assume an interior temp of 70F, exterior 12F for a 58F delta. For any double pane windows of unknown U-factor or any single-pane + storm, and exterior doors use 0.5 BTU/degree-ft. For all 2x4 framed wall area with at least some type of insulation use 0.1 BTU/degree-ft, for any 2x6 use 0.08. For an attic with anything better than sloppily installed R19s use 0.07. For uninsulated above-grade foundation down to a foot below grade, use 1BTU/degree-foot.
A typical 1800' house will have about 270' of window, and assuming a couple of exterior doors, call it 40' of door for 310 square feet of window + door:
U0.5 x 310' x 58F= 8990 BTU/hr
A typical 1800' 2-story will have 900' of attic floor:
U0.07 x 900' x 58F= 3654 BTU/hr
Assuming a perimeter of say 180' and 2' of above/near grade foundation for 360' of U 1.0), and a basement 15F colder than the upstairs when it's +12 F outside you're looking at.
U 1 x 360 x 43F= 15,480 BTU/hr
Assuming 10' per story and 180' of perimeter you have 1800' of gross wall area, less 310' of window & door leaves 1490' of U0.1:
U0.1 x 1490 x 58F= 8642 BTU/hr.
For 900' of U 0.07 attic you get:
U0.07 x 900' x 58F= 3654 BTU/hr.
Add it all up and you're at 40,420 BTU/hr. Add 30% 'cuz you live in the absolute DRAFTIEST house in Westchester (or always sleep with the windows open, even when it's +12 F outside) and you're still only at 52,546 BTU/hr, a load still covered by the -60 running with 160F output.
And those U-factors presume some pretty crummy & poorly installed insulation- reality is almost always better than that (or could be made better than that at very low cost). You'll note the biggest single number is usually an uninsulated unheated basement, which is an upgrade needed by more than half the homes in Westchester county NY. It's not super-cheap to retrofit foundation insulation, but there are lower cost and higher cost ways to get there. Using even intermediate-cost methods (say, 2" of closed cell spray foam + intumescent paint, at ~$3 per square foot) it's worth it, even at buck-a-therm gas.
Seriously- take the time to measure up your house on a room by room basis and use a spreadsheet tool to come up with the numbers- they're a lot lower than your bidding contractors think. Buy some low-E storms to retrofit on those colder rooms, or install more radiation in those rooms, and buy some air-sealing & insulation if you think it's still too drafty.