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  1. #1
    Join Date
    Sep 2011
    Location
    Westchester, NY
    Posts
    4

    Mod Con boiler with radiant floors

    Im installing a ModCon boiler with outdoor reset into a split level house that had previously had aluminum fin tube radiators throughout. It now has three zones plus DHW. 1) Basement with 12 feet of slant fin baseboard 2) first floor with radiant tubing under hardwood 3)second floor with the original had aluminum fin tube radiators. I dont have a problem setting the outdoor reset curve for the radiators and baseboard but that will also affect the radiant. The way I see it I can go two ways with the radiant zone, either I install a mixing valve and set the water temp for 115+/- on design day and see what happens when its 50 outside and the reset drops the boiler temperature or I install a set point mixing valve and set it to keep the water temp for 115+/- always. Any help would be much appreciated.

  2. #2
    Join Date
    Jan 2007
    Location
    Mn the state where absolutey nothing is allowed
    Posts
    1,334
    i would check out tacos radiant mixing block.

    that little gem will do everything your asking for
    my boss thinks its possible to repeal the laws of physics

  3. #3
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    The 3 zones seem to have

    a wide temp range at any given outside temp. Really high for existing fin base basement and 2nd and much lower for radiant first floor. How are you delivering water at such different temps? Can't be from same manifold
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  4. #4
    Join Date
    Mar 2001
    Location
    Washington DC
    Posts
    73
    I'd probably just mix down the radiant with a thermostatic mixing valve. The zone thermostat will limit overheat. The Taco RMB looks interesting, I used something similar (an Automix) in a wood boiler install, and setting it up was a PITA. Pricey. But doesn't entail the same high flow-resistance/head as a thermostatic mixer.

  5. #5
    Join Date
    Sep 2011
    Location
    Westchester, NY
    Posts
    4
    All three zones are connected to the same manifold and the boiler varies supply water temperature from 110* to 180* based on outside temperature. I know I need a mixing valve but I am getting opposing opinions about the temperature of the radiant loop. Should I keep a constant temperature in the floors all season long or do I lower it as outside temperature increases.

  6. #6
    Join Date
    Sep 2011
    Location
    Westchester, NY
    Posts
    4
    Quote Originally Posted by TGrettler View Post
    All three zones are connected to the same manifold and the boiler varies supply water temperature from 110* to 180* based on outside temperature. I know I need a mixing valve but I am getting opposing opinions about the temperature of the radiant loop. Should I keep a constant temperature in the floors all season long or do I lower it as outside temperature increases.
    Correction
    All three zones are connected to the same manifold and the boiler varies supply water temperature from 110* to 180* based on outside temperature. I know I need a mixing valve but I am getting opposing opinions about the temperature of the radiant loop. Should I keep a constant temperature in the floors all season long or do I lower it as outside temperature decreases.

  7. #7
    Join Date
    Mar 2001
    Location
    Washington DC
    Posts
    73
    Had it right the first time. I wouldn't include an outdoor-reset mixer on the radiant loop unless (maybe) you're in a really extreme climate. Unnecessary complexity. The biggest value of the outdoor reset is modulating the boiler, and that's going to be controlled by the higher-temp loops most of the time.

  8. #8
    Join Date
    Jan 2008
    Location
    s chester county,pa
    Posts
    144
    what boiler are you going to use?

  9. #9
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    TGrettler

    Your radiant floor temp should be known to you when you installed and DESIGNED it. the max water temp is a function of how much Surface Temp/BTUs per SqFt you needed and. the covering (carpet or wood floor or ?
    with the tube spacing. You needed that info to design it in the first place. Have you inherited a system you don't know anything about.

    And yes that is the max on that design temp day, you can benefit from temp reset to save money but mostly not overheat the house. By the time the stat stops the water flow the floor will keep delivering warmth. Problem? is with reset temp you are not going to have those stocking feet friendly surface temps that are so comforting. Reset is pricey so you may opt for a simplier approach ie just T stats with mixing valves as suggested by keith w

    Full disclosure, I am a duct guy this may be just enough info to get me into trouble
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  10. #10
    Join Date
    Sep 2011
    Location
    Westchester, NY
    Posts
    4
    Thanks for the info guys, I'm using an HTP Elite boiler. I spoke to the manufactures rep and he suggested using a standard mixing valve (not a set point) and setting it for 115* while the boiler is producing 180* water simulating design day. He did make it clear that is I want to get it right it will require tweaking to find that happy medium.

  11. #11
    Join Date
    Jan 2008
    Location
    s chester county,pa
    Posts
    144
    the weil mclain has 3 temp settings. you can set up 1 for dhw 1 for hi temp and 1 for low temp.

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