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furnace over heating hi return temp

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creger.robert
creger.robert Posts: 116
in Gas Heating
IMG_3281 hammond.jpeg

furnace return temp over 80 degrees-4 zones blower shuts down any thoughts

Comments

  • pecmsg
    pecmsg Posts: 7,487

    serious duct leakage!

  • creger.robert
    creger.robert Posts: 116

    ductwork has 2" of insulation inside of duct

  • pecmsg
    pecmsg Posts: 7,487

    No

    Openings, supply getting into the return.
    the return cannot be higher theN The room temp.

  • creger.robert
    creger.robert Posts: 116

    plus humidifer 7" on duct

  • creger.robert
    creger.robert Posts: 116

    the bypass dumping from supply plenum to return i have closedoff

  • creger.robert
    creger.robert Posts: 116

    raise cfm static also raises

  • pecmsg
    pecmsg Posts: 7,487

    A7” duct at best will raise 1 maybe 2*F

  • creger.robert
    creger.robert Posts: 116

    thank you

  • mattmia2
    mattmia2 Posts: 17,995

    is the zone damper opening for the zone that is calling?

  • HVACNUT
    HVACNUT Posts: 7,656

    The blower shuts down? If it was making limit, the burner circuit should open, but the blower continues to run to cool the HX. What's the heat rise and maximum SAT?

    What model furnace? Is there a code?

  • EBEBRATT-Ed
    EBEBRATT-Ed Posts: 20,946

    With high return temp maybe, the blower is tripping overload? I don't think it should at 80 deg but possible.

    Where is the return getting the 80 deg from? What is the space temp while this is happening.

  • ratio
    ratio Posts: 4,304

    What's the return temp before & after the bypass ties in? That's a pretty big furnace, if just one zone closes you're going to be bypassing more than a bit of hot air. Is it a two-stage unit? Some zone control panels can stage down the unit, or just disable high heat.

    You can also see about adding more minimum air to the zones, so you bypass less, too.

    GGross
  • creger.robert
    creger.robert Posts: 116

    my return is 83 degrees supply as high as 127-it is a 2 stage furnace with 5 tons of air

    should i try 1st stage only on heat

  • pecmsg
    pecmsg Posts: 7,487

    why is that return so high???

  • creger.robert
    creger.robert Posts: 116

    that is question zones are running 72 degrees area

    leaking around bypass possibly

    i believe ductwork is undersized 2" of insulation on inside of duct

  • pecmsg
    pecmsg Posts: 7,487

    that’s not from wrong insulation

  • ratio
    ratio Posts: 4,304

    There should be a temperature rise listed on the sticker of the furnace. As long as that's not exceeded, the DAT is fine.

    You have to be sucking too much hot (supply) air into the return, that's really the only (sane) way the return temp can get so high. It's just a matter of finding where it's happening. A thermal camera is your friend, but a simple thermometer will work too. Check the air going in to any returns and before & after the bypass

    It sounds to me like one or more of the zones are satisfying and closing down, so the bypass has to open to keep the airflow through the furnace up—which from your drawling seems to feed directly back in to the return. Or, if this is ceiling supplies and returns, it's recirculating.

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