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where to set boiler for pex

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kinda sounds like your running a radiant system without any mixing or flue condensation protection ,what model boiler is this ,if it is a conventinal cast iron atosphermetric boiler at the 140 setting you may be asking for future promblems,can you post a picture of the boiler installation ?If this is a modulating condensing boiler then that 140 aquastat stting may be correct for your system layout ,but in my book running a cast iron boiler at 140 for a radiant system with no condensation protection is asking for promblems peace and good luck clammy

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  • phil the limey
    phil the limey Member Posts: 31
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    just had hydronic heat installed, just kinda second guessing (as im prone to do) installer said to set boiler at 140 degrees, to run through the standard white 1/2 pex. burnham rep says boiler should be set at 180. i trust the burnham rep knows his stuff, but is there a problem running water at 180 through the system? it does not seem to exceed the limits of the pex. why would the installer say to set it at 140?? system pressure is 12psi.
    ground floor is concrete, with tubes about 1" up from bottom of concrete slab. upper floor has the tube stapled under the floor material.
  • Brad White
    Brad White Member Posts: 2,398
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    Sort of like buying a car

    and having the salesman and manufacturer each telling you differently how far to press the accelerator... :)

    The water temperature is not arbitrary, at least if you want maximum comfort. What is more, each flooring type needs in all likelihood a different water temperature. Concrete would run cooler, staple-up warmer, in general terms. Assuming equal heat loss densities this would hold true. Given that many concrete floors have a tile covering and wood is, well, wood and that both can have carpet, take your pick.

    But the point remains, you have different densities and different initial conductance. You are right to raise this. (The issue, not necessarily the temperature.)

    Simply, you need the ability to give each floor the correct temperature and at a rate matched to the heat loss of the space. This means a mixing manifold or other means for each.

    The staple-up floor's required temperature will likely govern the boiler temperature and the concrete will need a mix-down, chances are. If you use the boiler to make domestic hot water, you should have mixing devices on both floors to prevent hot spikes to the floors when domestic hot water is calling.

    Once you get your water temperatures established for the coldest day, you can then set each to a heating curve, lowering the temperature for the many days and hours when it is well above design cold outdoors.

    The boiler itself, if high temperature, needs protection (as Clammy noted below). The boiler will then have it's own heating curve, albeit limited in range, to protect the boiler. Your floor water temperatures would well range from near-room temperature to the low 100's for concrete to 140 for the staple-up. This is entirely within the range of what PEX will handle. See the PEX tubing itself; pressure and temperature ratings are printed right on it.

    Keep in mind that being installed now, your density (tube spacing) is fixed. Varying the temperature is the only variable you can effectively use to control output. If the spacing is less than was possible, you will need to run warmer water. Just and FYI.

    What you have sounds like it can be worked with but you need more control in my opinion.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • phil the limey
    phil the limey Member Posts: 31
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    as far as condensation protection goes, the flue run to the outside is almost horizontal, and the flue gases are pushed by a fan. there is an inverted tee on the horizontal flue section, and the bottom outlet of the tee has a reducer in the center, to which is attached loop of clear plastic tube to collect condensation. is this what you mean by condensation protection?

    the boiler is a burnham spirit
  • Brad White
    Brad White Member Posts: 2,398
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    More to it than that.

    The Spirit is a medium efficiency boiler which means it does not operate in a condensing mode (nor would you want it to). It has sealed or semi-sealed combustion and induced-draft which means you do not need a chimney. It does lower the flue gasses to a point where they will condense and that is what your stack drips are about. That is part of the operational design.

    The boiler protection we are talking about is within the boiler itself. You need to keep your return water temperature above 135 degrees F to avoid this. Your floors on the other hand, can see deeper reset which is why we would want them independently controlled down to even near room temperature.

    A Mod-Con (modulating condensing boiler) has the benefit of practically no low return water temperature limit and actually thrives on the coldest return water you can give it. For this reason, radiant floors with return water temperatures well under 100 degrees and often near room temperature are a great match.

    The Spirit is a fine boiler, don't get me wrong. It is more efficient than most cast iron boilers but it is still a cast iron boiler. Prolonged condensing and re-evaporation on the surfaces will shorten the life and void the warranty.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
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