When it is close, you need some experience with the program. Your heating contractor should provide a proper heat load that looks something like this the attached.
If you tighten your house up, you have to consider an energy recovery ventilator, more especially if you suffer long winters like we do here in Minnesota, similar to yours in AK. No one can, or should guess about heat loads e.g. "drafty" and "a lot of glass" don't really help the designer though both are critical to estimating heat loads. If we go with your numbers, discounting x.95 efficiency factor the 104mtuh output of the 110 would appear to cover it, just. Unless you have small zones (controlled by thermostats) that might short-cycle the boiler and considering you currently have a high temperature system with fin-tube baseboard and fan coil, you are likely to use the low fire without short-cycling.
When in future you add a slightly lower temperature radiant floor the minimum fire of the boiler may come into play. If a boiler is over-sized such as your current boiler, it will short cycle during the coldest weather burning more fuel and leaving you less comfortable. A modulating condensing boiler such as the Lochinvar Knight you are considering will modulate the flame after considering the outdoor temperature and only fire to the design water temperature your contractor programs into the machine.
So there are several things to consider before you size your new boiler. First is an accurate heat load for each zone. An over-sized boiler will short-cycle (go on and off) and suffer the same problem a city cab has with stop-and-go traffic, high maintenance and fuel costs. The Knight has a minimum fire rate and the higher the output, the higher the minimum fire-usually. The notable exception to this rule is the estimable IBC boiler made in Canada which had one of the lowest low-fire outputs and ranges to 150mbtuh inputs i.e. 150,000 British Thermal Units per hour. Think of a BTU as the heat generated by an old fashioned stick match.