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New Gas Boiler & DHW - Unsure of heat load and calculations from company
Moved into a 1906 built house last June, which had an old cast iron FHW boiler that had been converted from oil to gas and appears to be from the late 70's, paired with a 7 year old AO Smith DHW that already is corroding and needs to be replaced.
We're planning to switch to a ModCon paired with an indirect DHW, but am a little hesitant on trusting the one set of Manual J calculations I've received, as other contractors we had in for quotes seem to have differing opinions.
The house is 2591 sq ft, with cast iron radiators on much of the first floor (slant fin baseboard it looks like in the kitchen), along with radiators on the 2nd floor and then the baseboard again on the smaller 3rd floor. We live in Mass, so climate zone 6a, and currently have basic insulation (from what MassSave could tell) in terms of the walls and attic area.
We're planning to insulate the attic/roof deck and rim joists with closed cell spray foam, and like doing the walls with blown in cellulose, so assume we'll see a good reduction in heating needed, and here's where I need the help.
Does a heat load of 79743 btuh sound right for what I've described? I am just a normal homeowner, so don't have the expertise, but wanted to get the opinion of others before moving forward. The contractor is recommending we get a 125 000 btu ModCon with a 5:1 turndown ratio, but if their Manual J is right, I am thinking a 90/100 btu unit is more appropriate, and will prevent short cycling for smaller load areas like the Kitchen (which is on its own thermostat).
Any and all comments and input are welcome, and happy to provide more information or even a redacted copy of the Manual J we received if it helps.