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  1. #1

    How measure rise temperature

    I am using a infrared thermometer to measure my in and out temp from my furnace. The values I got are 63 in and 76 out. I just measure 3 feet from the burners. Is that correct?

    I think my out temp is too low. Actually I doesn´t look hot, I can stand my hand on the duct for minutes.

  2. #2
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    IR thermometers aren't accurate for temp rise checks.

    If your duct is insulated, then you should be able to hold your hand on the duct.

    Put a room thermometer at the closest supply to the furnace, and see if it doesn't read higher then what your IR is reading on the duct surface.
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  3. #3
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    Nov 2008
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    I'd think you could check your IR meter calib. by aiming at a metal cup containing a mixture of melting ice and water; it should read exactly 32 F.

    Some thing with a small specific heat capacity, e.g., a paper cup, in a room at 72 F when held near the thermostat should read 72 F.

  4. #4
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    Quote Originally Posted by andersen View Post
    I am using a infrared thermometer to measure my in and out temp from my furnace. The values I got are 63 in and 76 out. I just measure 3 feet from the burners. Is that correct?

    I think my out temp is too low. Actually I doesn´t look hot, I can stand my hand on the duct for minutes.
    Based on the verbage of your question one can only believe your not a pro in the industry but perhaps a homeowner looking for answers.

    That being said if your having issues, please call a professional in the industry.

  5. #5
    the IR thermometer read very well the black connection between the ducts but cannot read the duct. The delta temp now looks ok 50F.

  6. #6
    Join Date
    Mar 2008
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    IR guns read "surface temp", and they only do that with some accuracy when there isn't a glare.

    Take your readings close to their source. Return can and transition from the furnace OR transition and supply plenum for the evap. Some people drill holes for delta T, I use and ice pick or scratch awl.

  7. #7
    Join Date
    Dec 2002
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    Quote Originally Posted by Skip 2 my lou View Post
    Some people drill holes for delta T, I use and ice pick or scratch awl.

    Randy, when you as old as Mr. Bill I just feel the transition & Plenum for delta T.
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  8. #8
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    Mar 2008
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    Quote Originally Posted by Mr Bill View Post
    I just feel the transition & Plenum for delta T.
    The Plenum Whisperer?

  9. #9
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    Nov 2008
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    duct temp

    "Most infrared meters sold for less than $100 have the emissivity value fixed at the factory for 0.95. That makes them useful for many organic materials but renders them inaccurate when used with any other material."

    Shiny metal = emissivity around zero.
    Dull black paint = emissivity around 1.0 = black body.

    http://en.wikipedia.org/wiki/Black_body

  10. #10
    Join Date
    Mar 2008
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    Houston, Texas
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    Quote Originally Posted by WhoIsThat? View Post
    "Most infrared meters sold for less than $100 have the emissivity value fixed at the factory for 0.95. That makes them useful for many organic materials but renders them inaccurate when used with any other material."

    Shiny metal = emissivity around zero.
    Dull black paint = emissivity around 1.0 = black body.

    http://en.wikipedia.org/wiki/Black_body
    Don't forget how the temperature of the actual gun affects the reading. If the gun is cold the temp reading will be lower, and if it is warm the reading will be higher. This is true on ever IR gun I've ever used (you results may differ.) The "super insulated storage box" would improve the readings, but not very practical.

    I still have one tucked away in my veto, usefull tool, you just have to know it's limitations.

  11. #11
    Join Date
    Nov 2008
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    Quote Originally Posted by Skip 2 my lou View Post
    Don't forget how the temperature of the actual gun affects the reading. If the gun is cold the temp reading will be lower, and if it is warm the reading will be higher. This is true on ever IR gun I've ever used (you results may differ.) The "super insulated storage box" would improve the readings, but not very practical.

    I still have one tucked away in my veto, usefull tool, you just have to know it's limitations.
    I'm glad you're telling me all these limitations; I was all set to buy one for using it as a non-contact way of "seeing" faulty (hot) electrical connections.

    I'd think more expensive meters would correct for meter case temp. It's just another (thermistor) input plus an A/D convertor for the onboard uP.

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