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Mod-Con system design question.. Fewer zones = better?

CrispyCrispy Member Posts: 12
1200 sq. ft. 1890 gut-job renovation in Northern NY. New insulation. 2 beds up, one down. 2 full baths. IBC DC 20-125 combie. Heavy hot water load already addressed here.
I have read and learned a lot on the forum. I have radiant and a couple cast iron radiators including one of those massive cast iron baseboard units on the first floor. Baseboard on the second floor.
Based on what I’ve read, it seems like my best chance at achieving condensing temperatures, avoiding short-cycling and just keeping things simple, two zones might be the way to go. I’m thinking of plumbing my iron rads in the secondary loop first, baseboard second, radiant last. To keep mass as large as possible and to avoid “micro-zoning”, I’m thinking of putting all the first floor on one zone and all the second floor on another. The house is small and open plan.
Do I have the right idea? I will include everything to give me balance and adjustment options. Thanks, C.


  • hot_rodhot_rod Member Posts: 12,891
    It is nice to have individual control on bedrooms, depending on how you use the various rooms. TRVs are nice control methods as they are not a bang/ bang type control.

    A room by room load calc would help see how the heat emitters match up to the loads with the building upgrades and the lower SWT you are targeting.

    The lowest turn down on that boiler matched with a well insulated small square footage, mild days will still present some short cycling.

    A small buffer will help. It really depends on how close to perfect you want to get
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • delta Tdelta T Member Posts: 807
    Are you doing a home run set up (supply and return to each radiator)? We need some more info, a piping diagram of what you have in mind would help a lot. What kind of temperature protection are you using for the radiant? Is the radiant in a slab? staple up? Have you done a room by room heat loss?
  • CrispyCrispy Member Posts: 12
    edited September 2019
    I have run most of my 1/2”/under floor/4’ alum track/2 per bay radiant and kept the runs at ~200’. Thought about putting the rads together on their own loop. Haven’t done the upstairs yet. Using a garden variety mix valve (don’t have it yet). Downstairs floor plan is open at 22,000 btu/hr. heat loss. Didn’t do a room-by-room upstairs. House is on a 600 sq. ft. footprint. One room up is big at 300 sq. ft., the rest is cut up for bed, bath, laundry.
    I get your point HotRod but not sure it’s that important up there. What’s a TRV?
  • hot_rodhot_rod Member Posts: 12,891
    If you can manipulate the emitters to all run on one temperature. Did you run a design to see what SWT the underfloor radiant requires?
    Suppose it requires 120F on design, size the rest of the emitters to give you the output you need at 120F also.
    This will simplify trying to supply multiple temperatures, simplify piping and zoning.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Solid_Fuel_ManSolid_Fuel_Man Member Posts: 1,925
    One temp is the way to get it as close to perfect. I run my cast iron at radiant slab temps and it works well.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
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