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Did a Heat Loss calc and I'm surprised at the result. What do you think?
So I did the heat loss calc, as suggested, for my 3500 sq ft of heated space (natural gas boiler with baseboards). I have many large double paned windows, multiple rooms with high ceilings, and a bunch of skylights in various rooms. I was very surprised that it appears to be reporting I need a 65k btu boiler (that's what the calc'ed numbers mean, correct? Says Heat Loss BTU/HR = 64718). I'm surprised because I got 3 quotes and 2 said I needed a 100k btu mod/con with indirect water tank and 1 said a 110k btu cast iron boiler. Only one appeared to be gathering detailed measurements for a heat loss calc.
A few things that could affect my numbers:
1) I was surprised that I wasn't entering my actual baseboard lengths in each room rather than just seeing the suggested. Am I supposed to enter that somewhere?
2) I have insulation but I don't know what type. What's a good assumption for a large house built in 1989? I chose 2" insulation for walls and ceilings along the roof
3) I do have some large open entry ways between rooms that are hard to combine into 1 room. Like a living room with 7.5' ceilings that opens up to a foyer with 16.5' ceilings, so I left them separate.
4) I did outdoor temp of 20 degrees (Massachusetts and looking at temp history seems like it's typically 22 in the coldest months) and an indoor temp of 72 degrees, which is what we often use with kids. It never asked me but it said design water temp of 180 degrees. Are these good numbers?
5) If it's an indirect water tank, it never discusses water demands, which can be high for us with a family of 5.
6) I did not record interior doors to heated spaces or entryways.
So what do you think? Does a 65k btu boiler seem inline? Also, does this tell me whether or not I'd be better off with a mod/con vs a cast iron?