Best Of

As @delcrossv and @mattmia2 say, with a little oil (don't overdo it) and some attention to the motor mounts, that thing will run another century or so without problems. The coupler springs are the weakest part, and paying attention to the mounts will keep hem happy.

And the same pump is still made. Don't mess with success…

Oh and one more thing: it's within a percentage point or two of any "modern" pump in terms of efficiency.

You might contact the B&G rep in Seattle, CHC, see if they have the motor mounts and spring coupling. They would probably have a motor that fits also, if you want to buy a spare. Replacing that entire pump with another 4 bolt type may be expensive. Or changing flanges and piping with that insulation may be a lot to get into.

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Viessman is considered top of the line if you have someone who knows how to service them. To me tankless water heaters are problematic.

You need a heat loss calc as @HVACNUT mentioned. I would say an 80K boiler would do the job.. Why put in more than you need it is just more expense and the smaller boiler will work better. I used a 50K output in my 1100 sq foot house brick stone and cement block with no wall insulation. I doubt you need a 100k with your insulation and windows.

Although a Heat loss is best you can add up the output of you baseboard to get close I doubt you have over 80K of basebord.

You don't install a boiler with an output larger than the baseboard can output.

Now someone has to start making those iron hex foot raisers in 1" intervals that American Standard produced in the 1920s.