I'm in the same situation as most people around here (replacing an old oil boiler to a new natural gas system). My house, about 1600 square feet, was built back in the 1950's (Massachusetts). I'm in the process of converting my old oil boiler (115k BTU with a coil/tankless water heater) over to a high efficiency gas boiler/indirect water heater. I recently replaced all of the windows in my house with high efficiency windows but the insulation is pretty lousy in the house. I have 2 full bathrooms and there are 4 of us living in the house so showers/baths go every night. 1 last thing, I have 2 zones in my house and the house is heated with cast iron baseboards (which I've been told are very good) in most rooms.
Now to the question, I've had a number of different contractors in here over the past few weeks but only 2 have done any type of 'math'. 1 did a full heat-loss calculation and the other just measured the baseboards. The one that did the heat-loss calculation told me that I could get away with an an 80K BTU boiler (which he later up'd to an HTP EliteFT 110k BTU) with a 40 gallon indirect hot water heater (Plug N Go PRO41ZPG) while the guy who just measured all of the baseboards told me that I needed a 140k BTU boiler and recommended a Buderus GB142/45 (160K BTU) with a 40 gallon Superstor.
Based on the great feedback I've seen on this site, I'm confused. In one aspect, I trust the company that did the full heat-loss calculation, but on the other hand, the 2nd contractor (who measured the baseboards and supposedly got the boiler sizing requirements from the local Buderus sales rep) told me that I needed the higher BTU's to support the indirect water heater as well as the heat.
I don't want to oversize my boiler but I also don't want my family to be cold in the winter - any suggestions on who I should believe?
Thanks for your help!