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System design help.

idahofunk Member Posts: 1
Long time reader first time poster here. Thanks for having me.

I'm designing / installing a heating system for a building I'm redoing and its mine.
I've been installing HVAC systems for 15 years, but am struggling with this one as its mine lol.

The building is roughly 4k sq ft solid brick with a spray foam envelope (very efficient)
The end goal is to have 9- 300 sq ft bedrooms w/ bathrooms and another 600 sq ft suite all heated with HW baseboards zoned separately with DWH (calculating around 20gpm need if all showers were being used.)

I've worked with Noritz and Navien and intend to stick with Navien for this build.

Thus far I have determined to run an NCB-240 combi unit as primary with 2 NPE-240a cascade to handle water demand and carry 6 zones of heating with it.
Another NHB-150 would complete the heating requirements on the remaining 5 zones (suite to have 2 zones).

My question is does this sound like the best way to go both in up front costs as well as long term. Its the best middle ground I've been able to come up with myself but I'm suffering from paralysis by over analysis because its my own project and not a customer's.

I'll be running 1" iron for the gas w/ new tank setup so no supply limitations.

Being a residential heating guy this is a pretty big system and not in my typical routine. I'd also like some input on primary / secondary manifolds in this situation.

I have to split the heating zones due to the NHB not being able to cascade with a combi and just pipe them separately. That being said I was going to stay away from zone valves and run individual zone pumps out of the supply manifold allowing the internal pump to handle recirc when no heat is being called for.

I appreciate any input ahead of time!



  • ratio
    ratio Member Posts: 3,173
    3x 200k & 1x 150k ≈ 750k BTUH input if you expect everything to run at the same time. 1" sounds a little …scant… for that. Can the meter even handle that kind of flow?