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Rezoning: Multiple manifolds one zone?

I designed and installed a radiant heat system in my house a couple years ago, and am working on dialing it in. It's in the main floor of my house, pex-al-pex under gypcrete with tile floors. I used prefabricated panels (3 zone by valves) and a tankless heater from Hydrosmart, and the manifolds are RHT. I seem to have lost all the files I used on the system so the following numbers are estimates.

Zone 1: 300 sq ft: master bedroom, bathroom and closet.
Zone 2: 1200 sq ft: 2 bedrooms, bathroom, living room
Zone 3: 300 sq ft: kitchen, dining room, and laundry

My first issue is that my manifolds don't have flow meters and it turns out I was flowing water too fast through the mixing valve and got terrible groaning noises from the boiler as a result. I turned them down an unknown amount, but obviously need to know what they're flowing. Has anyone used the RHT flow meters? Any thoughts?

Second issue is that most of the whole house except the bedrooms are open, and south facing.
Zone 1 works great.
Zone 3 works great.
Zone 2 does a good job in the living room, but that often gets a lot of solar gain and the two bedrooms on the north side of the house get really cold

I was thinking of either splitting Zone 2 into two zones (it's currently 6 loops), which would require another valve on the panel and another thermostat (the taco controller can do 4 zones), or doing the split on zone 2 and combining the living room portion of zone 2 with zone 3. The reason they're not the same zone in the first place is due to the kitchen being a single step (i call it the death step because it nearly kills me daily) up from the living room. Could I put in a tee on the inlet and outlet going to two manifolds? Would I need to chain them together a different way?

Hopefully that makes sense, thanks!


  • arbakken
    arbakken Member Posts: 1
    Yeah, that's probably true. Here ya go! To reiterate the north bedrooms get cold, and I was considering either splitting zone 2 into two separate zones, or combining 2a with 3 somehow, and making zone 2b it's own zone. Thanks!

  • hot_rod
    hot_rod Member Posts: 16,278
    edited February 2021
    Bottom line is you need adequate flow to move the heat load. With a tankless heater you could be bottlenecked there?
    You can increase radiant output by either increasing flow rate, or increasing temperature. Only so much you can squeeze out by flow increase, it starts to taper off the % of additional output for extra pump power required, and velocity noise and wear becomes a concern. see below. 2-14 is a typical 250' 1/2" loop in concrete.
    Maybe try increasing the supply temperature and stay below 83F floor surface.
    What type of floor covering in the bedrooms? Lots of furniture covering the floor? Two outside walls on those bedrooms makes the load a bit higher probably.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • arbakken
    arbakken Member Posts: 1
    It's not that it can't get warm in those rooms, it's just that on a cold, sunny day (the main kind we have in Utah) the boiler and pump shut off because the solar gain gets the ambient temperature in 2a high enough and 2b, which gets no solar gain gets cold. Identical ceramic tile in all rooms.

    As far as flow rates are concerned, I have absolutely no idea what they are because I don't have flow meters on any of my loops. When I ambiguously turned them down to another unknown value, the boiler quieted down a lot. I also turned down the output temp from 120 to 110.

    I've got these manifolds: https://www.blueridgecompany.com/radiant/hydronic/807/rht-ss-hf-stainless-steel-high-flow-manifolds

    and either need to replace them or add flow meters to them (which will be a pain, but...)