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We need to replace a grossly oversized boiler that is also on its last legs and are hoping for some general recommendations given the somewhat unusual configuration we have.
The house is a three story colonial in eastern Massachusetts with ~2,500 sq feet of living space. Manual J and gas usage analysis both suggest max design day BTU of 75,000.
The heat is delivered through a mix of systems:
Single speed 59k BTU hydroair handler, with two zones off of it
Single speed 65k BTU hydroair handler, with three zones off of it
Hyrdroair radiator sized at 11k BTU
80 gallon DHW Superstor (212k BTU)
The present boiler is 400k BTU piped as primary / secondary.
What technology (modcon, modcon with buffer, medium mass boiler, . . . ) and size would you all recommend that would be efficient and work well with what seems like an usual mix of emitters. For cost reasons we are hesitant to replace the air handlers with smaller / more efficient models but could be persuaded if it is strongly advised as part of a system upgrade.
Thanks in advance.