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Proper boiler sizing and equipment
I have been reading through many of the threads here to try to form an opinion on a new system as a homeowner, and I need some help. In short, I have a 30+ year old oil boiler with indirect hot water that I want to replace. The house, located in Rhode Island, has about 3,500 sq/ft on the first two floors with about 500 sq/ft finished in the basement. It currently has an Axeman-Anderson that's labeled at 200k BTU, with 6 zones plus one for HW. I have talked to three contractors about a new system, and here's what I am getting:
1) An independent contractor - replace with a Pensotti DK2-8 (222k BTU DOE) - this contractor visited the house and measured the baseboards on one floor
2) Service company my oil delivery company recommends - replace with a Biasi B10-7 (193k BTU) and a HeatFlo HF-40 indirect
3) Largest company came and is doing a heat loss calc, but I think will cost 30% more than option 2 - Recommending Viessmann V-100 series
I did a quick heat loss calculation and I am coming up with just under 100k BTU. This seems low to me, but I understand that it is normal for it to be much lower than what was originally placed in houses decades ago.
I like the idea of a triple pass boiler, and potentially a ODR. My goal is greater efficiency, a reliable system, and a good servicing company.
1) Based on my general sizing stats, am I right that a 200k BTU boiler is way oversized? Is it possible that it actually would be better sized with something in the 100k range?
2) Any equipment recommendations? From this site, I see a lot about Viessmann controls being expensive, but they're good. I don't see much about Pensotti or Biasi. Is there an indirect tank that will last longer than others?
Any help or guidance you can provide is appreciated. Thanks!