Low-Mass Gas Boiler Design Needed

My existing hydronic system needs a fresh, low-mass boiler layout that runs on natural gas and feeds my baseboard radiators for space-heating only—no domestic hot-water integration this time. I’ll provide the current boiler specs, piping photos, and room-by-room heat-loss data as soon as we start.

What I need from you is a clear, code-compliant replacement design: proper sizing calculations, updated piping and venting schematics, pump selection, control strategy, and a parts list I can hand directly to my installer. Please base everything on modern high-efficiency, low-water-content equipment, and make sure the design plugs into the existing distribution loop with minimal disruption.

Final deliverable: a PDF drawing set (plans and details) plus a concise narrative and equipment schedule in editable format.