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Radiant Layout Zoning Help

Zanners Member Posts: 1
Hey everyone,

I'm trying to design a radiant floor system for a new single family house, I admittedly don't know much about radiant but I did some reading and tried to give it a shot.

I've attached a layout that I drew up, for several reason I could only have the two manifolds where they're shown on opposite sides of the house. The left side of house has much more heat loss (double high ceiling) than the right, about 30 btu/hr vs 18 btu/hr (per manual J). The insulation is good, R-21 walls, and in a northeast climate, radiant will be at sub floor for the first fl.

I routed the piping for the high ceiling areas to one manifold and the rest to the other, I calculated that the high loss areas should move about 2 gpm each and the low heat loss areas 0.9 gpm (for a ΔT of 10 deg). What I'm stuck at is how do I ensure that the areas that need more heat actually get it, would each manifold have it's own pump? Is it just a matter of different size piping to each one or decreasing the spacing in the high loss areas? There's also a radiant system for the basement that I didn't show, should these share manifolds and pump with the 1st fl system or be completely independent?

Any feedback on pumps/zoning would be awesome, critiques of the layout or any good resources that could help me with the design are great too, thanks!


  • hot_rod
    hot_rod Member Posts: 19,942
    30 btu/ sq ft is a lot to ask from a radiant slab. You may need some supplemental heat in those high load areas 

    Tightening the tube spacing will get a bit more output, maybe go 6” on the high load areas. 
    Use manifolds with balance valves to help fine tune it.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,127
    There are Upinor manifolds readily available that have flow adjustments on one manifold and flow meters on the other manifold. I'm sure the same feature is available on other brands.. putting the tubing on 6" centers will require more tubing and perhaps more loops. If you are installing Central Air Conditioning in the home, you can always add electric resistance or a water duct coil in the air handler for any time the outdoor temperature drops below design limits. If that is not an option, then some well places panel radiators or baseboards with higher temperature loops for those few cold days

    What size tubing are you using? I don't like to go over 300 feet when using 3/8" tubing and will usually stay closer to 250 feet. If you are using 1/2" tubing than over 300' per loop would be OK. But I'm conservative when it coms to radiant heat. A Do Over is rarely an option.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • JackW
    JackW Member Posts: 236
    I would strongly recommend reading "Pumping Away" by Dan Holohan.
  • Tinman
    Tinman Member Posts: 2,806
    Once you know the BTU/h/sf, then you need to determine the supply water temperature that’s needed to meet those losses. You have to figure in the R-value of the finished floor and the subfloor if you’re using plates beneath the floor, as well as the R-value of the insulation in floor joist spaces. And you’ll need to know surface temperatures limits for your floor coverings. That goes for the slab and edge insulation on the lower level. You’ll also need to deduct lower cabinets, appliances, islands, toilets, etc. from the area that can be used as part of the radiant panel. Once that’s all considered, then you’ll know whether supplementary heat is needed. 
    There’s a lot that goes into a proper design. 
    Steve Minnich
  • Zman
    Zman Member Posts: 7,472
    edited June 2022
    A few thoughts:
    1. 5/8" tubing is a PITA. Consider splitting the rooms into more loops and going with 1/2" throughout.
    2. 30 BTU/ft is a lot to ask. You could might consider some panel heaters like Runtals as a second stage of heat in those spaces. https://runtalnorthamerica.com/residential-radiators/. Another option would be to design a 2 temp system where the higher heat loss area would run at a different water temp. Yet another option would be a tekmar control that pulse modulates the zone valves on the zones needing lower temps so that the "average" temp in those areas stays lower and prevents overheating.
    3. You might want to rethink the location of manifold 2 to somewhere more central. The area around that manifold will be very warm
    4. If the areas needing less heat are bedrooms with fixed furniture locations, you could use less tubing and or transfer plates in those areas to reduce the heat output.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein