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Radiant hot water heating

Rocky1 Member Posts: 2
I have radiant hot water heat,with 6 zones (1 for each room); with 6 Honeywell non programmable thermostats. When set for 69 - 70 degrees, the heat will actually reach a temperature of 75 -76 degrees. I need to turn the thermostats off and let the house cool down for a few days.

Is it possible that the valves stick? How would I check them?


  • unclejohn
    unclejohn Member Posts: 1,749
    A Few

    Days? That's a long time for a house to cool off. Need more info. But would start with heat anticipater settings.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    When set for 69 - 70 degrees, the heat will actually reach a temperature of 75 -76 degrees.

    I used to get that when I knew nothing about hydronic heating, which my house has.

    I had an old GE boiler that was oversized about 2:1, and the boiler was running about 140F which was way too high. On the other hand it was not meant to condense, so it should not have been set lower. The near-boiler piping was done according to the GE manual (a few pages only), but not adjusted correctly. The manual did not say how to adjust it. The heat is 1/2 inch copper tubing in a concrete slab at grade. So the thermal mass was considerable. No outdoor reset. No reset at all.

    When I replaced that with a mod-con with outdoor reset, I learned about these systems and now it works just fine. I do not do setback though, since that does not work with slab at grade systems. It really takes about 24 hours to recover from modest setbacks, and several days to recover after the power here went out for almost a week because of Sandy.
  • Gordy
    Gordy Member Posts: 9,514
    edited January 2013
    What kind

    Of radiant.

    Concrete slab


    Staple up

    Suspended tube

    Sleeper system.

    What water temps are you using with the type of radiant you have?

    Is outdoor reset installed?
  • decoy86
    decoy86 Member Posts: 8

    Were your thermostats changed recently?  I had a simlar problem with my T-stats a couple of years ago.  I swapped out my old mechanical T-stats with a Honeywell digital heat only T-stat.  It was horrible.  The house was on fire.  There is a setting on them for radiant but it did not work well at all.  I swapped the Honeywell T-stats our for Uponor Radiant Heat T-stats.  Love them and they work wonderfully.  Go to Pex Supply on the web and type in Thermostat.  You will see a bunch that are for radiant heat only applications. 
  • Rocky1
    Rocky1 Member Posts: 2

    Concrete slab

    No new thermostats.

    Radiant heat contractor thinks home is very well insulated.

    With therms on, boiler doesn't start up until temp settings are raised.

    He advises keeping the settings to 3 degrees below the temp we would like.

    Might look at new radiant thermostats, also.
  • RobG
    RobG Member Posts: 1,850
    Outdoor air reset

    It sounds like you need a control strategy for your system. What temperature water are you putting into your slab? Your slab is a thermal mass. Once your thermostat reaches the set-point, it will shut off the boiler, however, all of the heat generated from your boiler is still stored in the slab and keeps on radiating after the thermostat is satisfied, hence overshooting the set point. If you install an outdoor reset device on your boiler you can vary the supply water temperature based on the outdoor air temperature. It may be simple or it may be difficult. depending on the system you have installed currently. Post some pictures of your boiler and piping and we can make some suggestions

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