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ONE ZONE OVERHEATS

FTWIII
FTWIII Member Posts: 14
in Radiant Heating
I LIVE IN A VERY SMALL CAPE AND I HAVE TWO RADIANT ZONES ON THE MAIN FLOOR. THE ONE IN THE BEDROOM WORKS GREAT. I SET THE T-STAT TO 64 AND IT MAINTAINS IT VERY WELL AND THE FLOOR FEELS WARM. I KNOW I HAVE DRAFTY WINDOWS AND THE ZONE RUNS MORE THAN IT SHOULD BUT THAT IS ANOTHER STORY.

THE REST OF THE FIRST FLOOR DOESN'T WORK AS GOOD. I SET THE T-STAT TO 65 AND USUALLY IT READS BETWEEN 69-72 DURING THE DAY AND TRHOUGH OUT THE EVENING. USUALLY WHEN I WAKE UP IT IS 65 OR 66. SO SINCE THAT THERMOSTAT IS ALWAYS SATISIFED IT DOESN'T RUN THAT MUCH AND SOME TIMES FEELS CHILLY.

I FEEL THE PIPING AT THE BOILER IS CORRECT. I HAVE AN 1-1/4" PRIMARY LOOP WITH A CIRCULATOR AND FLOW CONTROL. THEN EACH ZONE TIES OFF OF THAT WITH ANOTHER CIRCULATOR AND FLOW CONTROL. I WOULD APPRECIATE ANY FEED BACK. THANK YOU

Comments

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,206
    Overheating

    Something is causing flow to the first floor after the thermostat is satisfied.  You say you have a flow control.  If the flow control doesn't prevent gravity circulation, you might be getting hot water moving through the first floor zone even when the pump is off.



    You might also be experiencing a flywheel effect if your radiant tubing is embedded is extra thick concrete.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    flywheel effect

    I got that with my old oversized boiler into my at-grade radiant slab.The thermostat would call for heat. It would take several hours (like four) for the slab to warm up and satisfy the thermostat. By then, the slab was hot and would heat the house for four more hours.  Room temperature would vary from about 66 degrees to about 74 degrees.



    Now that I have a mod-con with a slightly oversized boiler, but with outdoor reset, this problem seems to be solved. I set ther thermostat to 69 degrees and it holds it except on very warm days when my two computers (one has a 650 watt power supply and 14 fans) and the sun load take it up to about 71F. A big improvement. And that happens only on days that get fairly cold at night, and quite warm in the cloudless daytime.
  • FTWIII
    FTWIII Member Posts: 14
    ONE ZONE OVERHEATS

    Thank you for your response. My tubing is stapled up against plywood and hardwood flooring. is there a way to add somekind of solenoid valve to stop flow 100% when that zone is not calling for heat? the flow control is only 3 years old. could it be bad? how would i know?
  • EricAune
    EricAune Member Posts: 432
    edited November 2010
    Can you post a picture?

    Can you post a picture of the boiler and its piping?  Is there just one flow control or are there two (one for each zone)? 



    Does the overheating zone have a lot of windows as compared to the other zone?



    A zone valve can be added but this will require draining of the system and some electrical changes as well.  A picture might help us see what is going on.

    There was an error rendering this rich post.

  • FTWIII
    FTWIII Member Posts: 14
    ONE ZONE OVERHEATS

    I WILL TRY TO GET A PICTURE POSTED.

    THE PRIMARY LOOP HAS A SA1" FLOW CONTROL, THEN EACH 2NDARY LOOP HAS A 3/4" (SWEAT) FLOW CONTROL.

    THIS ZONE DOES HAVE MANY MORE WINDOWS AND DOORS, BUT I WOULD THINK THAT WOULD HAVE THE OPPOSITE EFFECT. MY T-STAT IS ALWAYS READING 2 TO 5 DEGREES WARMER THAN THE SET TEMPURATURE.
  • Paul Pollets
    Paul Pollets Member Posts: 3,662
    Plates and Mixing

    If you haven't used aluminum transfer plates, the underheated zone may not be as responsive. Also, if the boiler has no mixing device, it's possible to send low return temps back to the boiler, which can cause major problems for cast iron boilers.  Installing plates is usually the solution, but proper mixing temps and boiler return protection shoudl be considered.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    How many mixes

    Is this all running on one mix temp? What influence does solar gain, cooking and people play on the zone that is over heating? What was the heat loss of the room that is comfortable and the room that is not. What water temp was needed to heat the space at design for both the areas?

    I always revert back to design before I even look at piping, etc. The starting point of troubleshooting radiant general lies in the design phase. It tells what I should have and then I adapt what is there. I would tend to say you have more of a design issue than piping, flow checks etc.

    There was an error rendering this rich post.

  • FTWIII
    FTWIII Member Posts: 14
    ONE ZONE OVERHEATS

    I like where you are going with this. I think solar gain has a big part. It is a small house and I have direct sun mostly all day. I also feel when we are home it gradually creeps up. The boiler temp cycles between 160-180 degrees. each 2ndary loop has a mixing valve. The thing that really puzzles me is that when I wake up at 6:30am, before the sun is out, it can sometimes be 2 degrees over.

    The zone that works well, is only a 12' x 12' room with 2 windows. That holds the set temp and the floor usually feels warm.
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