We are replacing a dead steam / hyrdonic sidecar system with a new radiant system. Radiant loops are installed & pressure tested, and the next step is to finalize the boiler / DHW plan. We would like some feedback, as this is not something we have planned before, and it's been daunting to research all of the pieces and get this far.
Total thermal load across the radiant zones is approximately 32-35K BTU/Hr, so the Greenstar 151 should be able to modulate down well (close to sea level), and still meet the indirect tank peak loads (~115K BTU) w/ DHW priority. Total flow for radiant loops is ~6.5 GPM, approximate breakdown (not including head loss for manifold + boiler piping + balancing valves):
Mudroom Zone: 1.5 GPM @ 3.5 ft. head
1st Floor Zone: 2.3 GPM @ 2 ft. head
2nd Floor Zone: 1.6 GPM @ 2 ft. head
Basement Zone: 1.3 GPM @ 2.5 ft. head
Indirect Tank (Ideal): 14 GPM @ 3.5-4.5 ft. head
Based on these numbers, it looks like the 3 speed Grundfos pumps should fit our needs with the available curves. The heated space is ~2250 sq. ft. (including basement) with 2 bathrooms, 1 dishwasher, 1 washing machine (very unlikely we'll ever pull more than 3 GPM of DHW for regular sustained loads, and that's probably an overestimate).
As this is our first time planning a heat / DHW system, any and all feedback is appreciated, as we don't know what we're missing or over-engineering.