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retrofit: funky existing radiant floor, some new radiant floor, brand new mechanical room. advice pl

xmorganx Member Posts: 18

I'm working on the plan for a new mechanical room in a house with a sort of funky existing radiant floor system. This is for my boss' new house (new to him, anyways), so on the one hand I'm kind of honoured he asked me to do it, on the other I'm a little worried that he doesn't quite get the existing system and is hoping I'll come up with something brilliant ( or that it will be my fault if it doesn't work right...). The existing system is radiant floor, but it's 3/4 steel mains (divided) with 2 common 1 1/4 steel returns (one for basement, one for ground floor). These are poured into the slab (in the basement) and into some sort of concrete panel on the main floor (think steel deck, but all concrete... or maybe the concrete panels have a top coat poured over them. I'm not really sure, but I've never seen anything quite like this before). I've added one section of warmboard-r on the main floor to cover a previously unheated section and will be heating the formerly cast-iron radiator heated garage (to be a playroom) with radiant floor (probably warmboard- maybe some sort of in-slab overpour). There is no gas service to the street, so we're using an electric boiler and indirect DHW tank, but will leave tappings for a future gas boiler (condensing) so that the system could later run bi-energy.

1- I originally planned to use zone valves on each existing main. BUT, 20 loops equals almost 3000$ worth of zone valves and this seems a bit unnecessary. New plan: divide into sections (basement, bedrooms, common space) and use balancing valves on each main to fiddle for different (and unknown) loop lengths. Ideas? Models?

2- I'm thinking 3 low-temp circuits: 1 for existing basement, 1 for existing ground floor and 1 for new warmboard on ground floor and in basement. Thoughts?

3- I usually pipe my indirect DHW directly into the boiler loop, because apparently we've had issues doing otherwise. Not sure how to do this with 2 boilers, one non-existant for the near future. Anyone had issues piping off primary? See diagram, then thoughts?

4- Thinking about using Taco iseries outdoor reset mixing valves but have never used before. Feedback?

5- Please note that diagram is intended to show concept only. Please ignore missing accessories, incorrect tee spacing and my less than extraordinary drawing skills.

Any input would be greatly appreciated.


  • Zman
    Zman Member Posts: 7,330
    Another idea...

    I am thinking you have far to many closely spaced tees. I would pipe the two boilers together on a common header. They would each have a circ and a check valve.

    This primary header would tie into the secondary with closely spaced tees.

     I would not use closely spaced tees for the secondary branch zones as it will cause a temp drop from one to the next. A generously sized supply and return header would be much better. You of course will need a circ and check valve on each zone.

    In your drawing, I don't think the water will ever get from the boilers to the zones, if you pipe it your way, you will need another circ on the main loop.

    I would pipe the dhw as a zone. I would use controls to give dhw priority over space heating.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 16,316
    hydraulic separator

    would also be an ideal option. Here is some design info and a common piping schematic for multiple inputs.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
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