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Radiant Design: Please Critique

TAGTAG Member Posts: 205
edited November 2019 in Radiant Heating
Sorry for the long post.

About to restart my problem project -- converting small (32'x50') multilevel 1870's stone church into my home. It's an almost gut rehabilitation after a fire many years ago. I'm trying to figure out how best to control the radiant w/o going overboard. The heat loss in under 60k. New two story kitchen addition (18'x27') attached to the back of the stone building --- closed cell foam throughout.

The lowest level under the kitchen and extending into about 1/4 of the stone building is a new slab with PEX. We poured white concrete -- this will be the finished floor. There is a big bathroom down there. The whole middle level of the stone building and the kitchen addition is now Warmboard that will be covered in white oak. The upper most level (Living room in the rafters) was not damaged and remains plywood subfloor/ finished wood floor. This upper level is about 3/4 of the stone buildings foot print. After much discussion and thinking -- asking question here last year. I think extruded plates and 3/8 tubing is best for retrofitting radiant into the living room floor level.

So ....... how do I control the three different types of radiant ? I have the smallest Viessmann 200 boiler w/ LLH .. it's around 60k. My plan was to add an indirect for DHW. Debating 42g or maybe the 50g due to the smallish boiler output -- just two bathrooms.

The slab level and living room are both dedicated areas. So my plan was to have a circulator out to a dedicated manifold for each. The new Warmboard is setup to be room by room zoned (if need be) -- bedrooms/bath/study/ loft and the kitchen. The warm board will need two manifolds because of the layout -- one in the stone building and another in the new addition

Since the Warmboard is the main part of the house. Was thinking that this should be the main boiler circuit w/ outdoor reset. The plates in the living room w/ 3/8" PEX will get the same temp. The Warmboard is 12" on center and the plates will be 8" or so .. I'm thinking they should be about equal output ? Or maybe a bit lower for the plates? That would be fine as the living room being up in the rafters is going to need less heat anyway.

Was thinking of a slab temp sensor to control the slab ... or I could use the second channel of the boiler and have a mixing valve to lower the water temp to the slab. Seems like overkill -- the slab level is partially underground and will not need a huge output. I could also use a static mixing valve or one of the Danfoss wax type.

Is there a way to have the two manifolds for the Warmboard on the same pump? The manifold for the slab and smaller of the two for the Warmboard can be in the mechanical room w/ the boiler and indirect tank. The other Warmboard manifold and the 3/8 for the PEX needs to be remotely mounted. There is no way to get all those PEX lines through the building.

FYI: I'm not doing this. I could ... and have. But, I don't have the time or desire. I'm just getting final bids -- but, the boiler piping and controls has not been determined. There will also be a full ducted system/ mini split for AC that can provide heat as well.

My thought was to set the boiler up with the LLH -- pumping away. Circulator out to each of the manifolds.

Is a thermostat controlling a circulator a reasonable way manage the living room manifold? or is a larger single pump and zone valves out to the manifolds the way to go with piping ?

I have not purchased them yet -- but Warmboard has thermostat controls on each loop of the manifold they sell and a wall thermostat in all the Warmboard heated rooms.


  • hot_rodhot_rod Member Posts: 13,198
    The best info to answer your question is the required SWT for all the various applications.

    If the supply temperatures are within 10 degrees or so of one another no need to add another mixing device.

    ideally in the design phase you play with emitters, spacing, etc to get all the SWT requirements as close to one another as possible to take complexity and cost out of the piping.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • TAGTAG Member Posts: 205
    Hot Rod: 10 degree is what I'm looking for. The Warmboard spacing is set by the nature of the product (12"). My theory with the 3/8 plates around 8" apart ... it's going to be close to the Warmboard's output. Less I would think ... that's fine for the space. The slab is another matter -- I'm thinking the same temp is going to be too hot. I need some form of control -- slab temp maybe? I'm thinking I should stick some form of bypass .. either a simple valve to bleed some cold ... or maybe some type of Danfoss. A mixing valve circuit seems like overkill.
  • ZmanZman Member Posts: 5,746
    Have you calculated the required water temp for each assembly?
    If they are close, you can run the same temp to all of them. A static mixing valve for the cooler temps should work well as it will track the outdoor reset curve the boiler is running. A thermostatic valve will disregard your outdoor reset.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • TAGTAG Member Posts: 205
    Z-man .. good point. What's the best way to pipe a static. Years ago I did a simple ball valve w/ an inline check valve on one of my systems. Is a 3 way valve better? The mechanical room is tight -- I'm trying to make sure I have some flexibility should I need to tweak things w/o having to ripe piping apart.

    I'm having another heat loss done --- The house has 5 levels all open to each other. So the actual heat load for each space is not as easy to determine. My main concern was to make sure the Warmboard would deliver the BTU/SF needed. I don't have the water temps in front of me for the Warmboard. The plates are a guess.

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