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How do you limit the max temperature for radiant?

rickgerv
rickgerv Member Posts: 22
Related to a previous post but different topic.
I understand the radiant floor runs at a lower temp than baseboard. I have radiant floor on floor 1 and baseboard on floor 2.

We're hitting some extreme temps in my region. I have an appropriate mixing valve installed, as well as a mod con with outdoor reset. In milder temps, radiant does run lower water temp than the baseboard. However, on colder days, the radiant runs at a higher temp that what's healthy for the floor.

Question is - Even if the radiant needs a higher water temperature to satisfy the thermostat setting, is there someway to cap it so it doesn't exceed 140 degrees. One simple solution is simply set the thermostat to a lower temp. But that's not always possible with my in-laws. spouse, kids, etc.

Plan is to add 2nd stage heating. However, I'm interested it whether my plumber should/could have put a control to limit the water temperature to the radiant. Can radiant be on a different outdoor reset curve than the baseboard zone such that each zone runs a different max temp or does it all have to tie to the same curve? Not sure if I have mistaken expectations thinking the radiant could somehow have a different max temp setting than non-radiant.

Comments

  • SWEI
    SWEI Member Posts: 7,356
    A simple high limit can be effected using a conventional fixed temp thermostatic mixing valve.

    BUT

    If you install the Tekmar 402 with a motorized mixing valve, that will manage the radiant floor temp independent of the main boiler ODR curve (which will be set for the higher supply temps required by the baseboard zone.)
  • hot_rod
    hot_rod Member Posts: 21,793
    rickgerv said:

    Related to a previous post but different topic.
    I understand the radiant floor runs at a lower temp than baseboard. I have radiant floor on floor 1 and baseboard on floor 2.

    We're hitting some extreme temps in my region. I have an appropriate mixing valve installed, as well as a mod con with outdoor reset. In milder temps, radiant does run lower water temp than the baseboard. However, on colder days, the radiant runs at a higher temp that what's healthy for the floor.

    Question is - Even if the radiant needs a higher water temperature to satisfy the thermostat setting, is there someway to cap it so it doesn't exceed 140 degrees. One simple solution is simply set the thermostat to a lower temp. But that's not always possible with my in-laws. spouse, kids, etc.

    Plan is to add 2nd stage heating. However, I'm interested it whether my plumber should/could have put a control to limit the water temperature to the radiant. Can radiant be on a different outdoor reset curve than the baseboard zone such that each zone runs a different max temp or does it all have to tie to the same curve? Not sure if I have mistaken expectations thinking the radiant could somehow have a different max temp setting than non-radiant.


    Are you measuring floor surface temperature, or the supply going to the zones on the radiant?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Rich_49
  • aircooled81
    aircooled81 Member Posts: 205
    Tekmar is fancy, very nice.
    They also have capability of utilizing a seperate pump for injection. If you have one primary loop for your boiler, and countless other secondary loops - dhw, radiant foor, convectors/baseboard, you can set this controller to meter the fixed water temp you want each indavidual secondary loop to maintain, while still keeping a flow through the loop.
    A flow check is helpful too, when you want to prevent hydronics from self circulating through convection.
    My Rules of thumb, max 120 to slab to prevent concrete damage, min 140 to convectors for adequate use.
    Just my O
  • gennady
    gennady Member Posts: 839
    Radiant heating is limited by floor temperature. At very cold days, if house is not tight, you would need auxiliary heat.
    Rich_49
  • hot_rod
    hot_rod Member Posts: 21,793
    A rule of thumb is 25- 27 but/ sq. foot output for a radiant floor panel. Some will say 30, but that would require almost every square inch of the radiant surface to be warmed and provide a consistent floor surface temperature. That may be tough to do even with 6" on center spacing.

    So as always, and this can't be stressed enough, the key is to know what each room heat load is. Maybe the radiant floor alone can match the load, in some cases not, and some supplemental heat is needed.

    Under-designed or radiated systems usually show up at or below design days, sometimes it takes years for that condition to present itself.

    Or something changes in the structure, air gaps open, window seals fail, insulation sags, basically the load changes.

    A change of floor covering can make a difference in floor output, and sometimes a large difference. Even throw rugs with foam padding below can greatly reduce output.

    Radiant ceiling and walls is another option for additional output. Panel rads may work well with radiant if sized properly.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • rickgerv
    rickgerv Member Posts: 22
    Hot rod.. i have a thermometer on the manifold measuring the water temp for the supply and return. So I am not measuring the floor temp. The floor temp of the Hardwood above the subfloor I think was getting to 80 on the zero degree days.

    But I was concerned because the supply water temp at the manifold to the radiant zone was getting to 160+. I would want to control it so that it was capped at 140 no matter what the outdoor temp is.

    Sounds like the 402 would do the trick but a cap could be set on the mixing valve too. 402 + labor + pump may have to wait a couple of years.
  • jonny88
    jonny88 Member Posts: 1,139
    Crude way for now what about lowering mixing valve so you dont get to 160 and make the system run more continously?
    Gordy
  • Gordy
    Gordy Member Posts: 9,546
    We can throw out all sorts of add ons, and strategies, but in short I would say @jonny88 suggestion would limit run away floor temps until the dip subsides.
  • Rich_49
    Rich_49 Member Posts: 2,766
    edited February 2016
    gennady said:

    Radiant heating is limited by floor temperature. At very cold days, if house is not tight, you would need auxiliary heat.

    This is too broad of a statement to throw out there . Even in a leaky house you cannot possibly know this for sure without performing room by room heat loss calcs , you know this to be true Gennady .
    Just one more reason to perform this type of heat loss , another discussion right now addresses fuel usage as as a proper technique . I stand by the room by room requirement since to determine what you are capable of using or if you will need supplemental also requires it ..
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
    Gordy
  • jumper
    jumper Member Posts: 2,206

    Yes. Floor radiant should have supplementary heating because when you need it you need it.
    hot rod said:

    A rule of thumb is 25- 27 but/ sq. foot output for a radiant floor panel. Some will say 30, but that would require almost every square inch of the radiant surface to be warmed and provide a consistent floor surface temperature. That may be tough to do even with 6" on center spacing.

    So as always, and this can't be stressed enough, the key is to know what each room heat load is. Maybe the radiant floor alone can match the load, in some cases not, and some supplemental heat is needed.

    Under-designed or radiated systems usually show up at or below design days, sometimes it takes years for that condition to present itself.

    Or something changes in the structure, air gaps open, window seals fail, insulation sags, basically the load changes.

    A change of floor covering can make a difference in floor output, and sometimes a large difference. Even throw rugs with foam padding below can greatly reduce output.

    Radiant ceiling and walls is another option for additional output. Panel rads may work well with radiant if sized properly.

  • Tinman
    Tinman Member Posts: 2,808
    I've never added supplementary heat for a radiant floor design unless the room by room dictated that I needed to. Never.
    Steve Minnich
    Rich_49CMadatMeSWEI
  • Rich_49
    Rich_49 Member Posts: 2,766
    @jumper said . " Yes. Floor radiant should have supplementary heating because when you need it you need it. "

    Thanks for your contribution to making radiant heat absolutely un affordable . The only time you'll need supplemental heat is when you need supplemental heat . It is your job to know when that is and inform the client what rooms might need it when it gets down to X* . If you cannot determine this you are not doing your job .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
    CMadatMeTinman
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Think the original poster is too focused on water temp vs Floor Surface Temp as HR pointed out. What do I care what my water temp is as long as it's giving me the btu/hr I need. Its surface temp that I'm worried about. An 80 Degree surface temp on design day, while not where I'd design wouldn't be an issue. I don't care if you're pumping 180 degree water to obtain it.

    It's more of a system efficiency conversation not an operating one. Why would you limit the water temp output if you need it and the floor surface temps aren't an issue. Especially for the minimal amount of time you're at design day temp.

    In your original post you stated you have a modulating condensing boiler with a mixing valve for the radiant, don't understand why you need another one unless whomever did the design and zoning now has you over heating one room and under heating another because of the heating curve at the boiler.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
    SWEIRich_49