My boiler is a 151,000 BTU Weil McLain WTGO-4 (oil and hot water, located in CT). After adding insulation to much of the house, insulating pipes, sealing drafts, installing networked thermostats to synchronize calls for heat, installing a smart circulator and new Hydrolevel, and switching to an indirect tank and cold start, it is extremely short-cycling--anywhere from 2 to 60 seconds once every ten minutes in winter temperatures, while keeping the house at 60-65°F and the water at 140° F. I.E., the boiler is running at most 25% of the time, and more frequently <10%. The burner cuts off at 190°; the boiler temperature gets up to ca. 216°.
The boiler is leaking, so I would like to replace it with a Buderus G115. A heat loss calculation yields 74,000 BTU at an indoor temperature of 55° F or 89,000 at 65° F, when it is 0° outdoors. With milder winters becoming the norm, during the uncommon cold snap, when it's zero out, it's nearly always night--and the thermostats set back to 55. It seems odd to pair a daytime indoor temperature with a nighttime outdoor one. It is also hard to square a heat loss of 74,000 BTU with a 151,000 BTU boiler that runs well less than half of the time.
I am not sure what size Buderus to buy (74,000 or 95,000). Any advice would be appreciated!