Unless this is a leaky older 5000'+ house with no foundation insulation it's unlikely that your heat load is big enough to warrant as big as the -110 in a MA climate. If it's broken up into several zones you may shorten the life of the -110 by short-cycling on zone calls, since the min-fire output is ~28-29KBTU/hr (which is more than 3/4 the measured whole-house heat load at my house at 0F. My house isn't new, and not close to code-min on insulation or windows, but I've tightened it up a bit since moving in.)
You might get the same comfort, better efficiency, and longer boiler live out of the -60, which modulates down to ~15KBTU/hr, which is less my average mid-winter load (and maybe yours), which would yield far fewer flue-purge & ignition cycles, and long, modulating burns for much less stress on the equipment.
If your calculated heat load at the
99% outside design temperature is even as high as 57KBTU/hr you'd be better off with the -60, and it would make very little difference to the overall system design, and might knock a few hundred off the quote. Even if the quote stays the same, I'd still go with the smaller boiler as long as it met the whole house load at the 99% condition.
How was the heat load/boiler-sizing determined? Did anybody do a formal room by room heat loss calculation? Do you have a fuel-use history on this place using other equipment? (An upper bound on the heat load is readily calculated by fuel use and name-plate efficiency of the prior equipment.)
Mounting the boiler directly to a poured concrete wall isn't much of an issue- it works fine.
But an
uninsulated foundation wall is worth doing something about in a MA climate too. At the very least consider buying a single sheet of rigid 3" iso (~R18), and mount it to the wall behind the boiler with 3/4" OSB or ply through-screwed to the foundation with 4.5" or 5" TapCons 16" o.c. and mount the boiler to the OSB/ply, then finish insulating the rest of the foundation later. In most 1-2 story MA houses an unsealed uninsulated foundation accounts for 15-20% of the total heat load (and fuel use), whether there's joist insulation between the first floor and basement or not.