I am not certain that I need a mod-con boiler. Here's the story:
I have a 4500 sq ft three story house in Minnesota originally built in 1914 and expanded in the mid 1980s. I am current running a Weil-McLain VHE sized at 165K BTU. The house has 127 ft of cast iron baseboard and 401 sq ft of radiator. Using tables found online to convert to BTU based on water temperature :
@140 degrees = 40,640 BTU/hr baseboard + 40,100 BTU/hr radiator = 80,740
@160 degrees = 57,150 BTU/hr baseboard + 52,130 BTU/hr radiator = 109,280
@180 degrees = 72,390 BTU/hr baseboard + 68,170 BTU/hr radiator = 140,560
I tried to use our heating bills to convert therms/HDD to estimate our actual heat load. Over the last 2 years, with mild winters, the coldest month appeared to need 94K BTU/hr.
This means that I will need to run close to 160 degree water to meet our heat loss on cold days. I might be under radiated for a mod-con. Does it still make sense to get a mod-con boiler?
BTW, I live in a small town and have been unable to find a local HVAC company that will run a proper heat loss calculation. The first company sized based on my previous boiler, the second company sized it by walking around outsize my home and filling out a worksheet, and the third company was interested in sizing by our radiators.
I tried to do a heat loss calculation, but based on our house size, the air infiltration rate seemed to be the dominant factor. Small changes in the factor make a big difference in the result. It looks like I will need a blower door test to size it correctly.