Combi Boiler Design Suggestions

GRod

Greetings,

I'm upgrading my boiler to a new Navien NFC-250/200H combi boiler. Here are my particulars:

3500sqft colonial home, 3 zones, fairly new construction (2013), 3 ecobee thermostats, NY (Long Island)

1st floor - 69 ft of slant fin baseboard

2nd Fl. - 71 ft of slant fin baseboard + bath has a small air coil in the bottom of a cabinet( bath is always the coldest room)

Basement - Hot Air Coil at Air Handler

I'm upgrading from my current system due to my indirect water tank needs replacement and going with this Combi unit.
My biggest question or concern is whether to go with individual pumps (like the 007e or 0015e, or Grundfos Alpha 1558) for each zone (3 circulator pumps)

OR

go with a delta-T or P pump with zone valves (sentry valves) ? Really trying to see which one is best for my case now that Im going with a mod/con boiler and trying to minimize short cycling. Dont know which one will be the best efficiency wise so that I can operate the boiler in condensing mode for the longest time possible even though I do use baseboards for heating my home.

Any feedback is greatly appreciated.

Thanks

hot_rod

69' at 500 btu per ft= 34,500 btu/hr, call that a 3.5 gpm required

71' is 35,500, call that 3.5 gpm also

What size is the air handler? call it 30,000

so a total load of 100,000 @ 20 delta you need to move 10 gpm

10 gpm is within reach of the small delta P circs like an Alpha 15-58

So 1 pump and 3 zone valves is my choice. The delta P circ will modulate with ZVs opening and closing.

Individual zone pumps to move a small 3 gpm load seems overkill to me, but plenty of opinions for pumps vs circs

That boiler can modulate down to 13,000 btu/hr. You want the boiler to be able to modulate down near the smallest zone requirement, so you are good there.

I would go into the control and limit heating output to maybe 100- 120,000 btu/hr

So now you have a boiler with 200,000 output in DHW mode, but you downsized it for heating loads. That helps limit cycling.

Outdoor reset is a nice feature if you take the time to dial it in.