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  1. #1
    Join Date
    Jan 2009
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    Reznor gas duct heater super hot on top

    Recently installed Reznor EDDU 300 (300,000btu) gas duct heater. Removed baffles to convert for higher cfm (5,500cfm) According to manual unit now has max throughput of 11,111 cfm and minimum throughput of 3175cfm. AHU supply air to heater is 5470cfm. When the heater is fired, the top of heater appears extremely hot, very quickly, as does double wall bvent.
    Temperature rise appeared rather minimal, in its rate of rise compared to immediate extreme rise of bvent and top of heater.
    How hot should the top of cabinet and bvent get???

  2. #2
    Join Date
    Aug 2015
    Location
    Buffalo,NY
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    1,033
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    The bvent shouldn’t get overly hot. Has anyone checked gas pressure?


    Sent from my iPhone using Tapatalk

  3. #3
    Join Date
    Jan 2009
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    Thread Starter
    Not yet, I just finished reading a little Reznor lit. about gas pressure. Test and balance guy has verified cfm past heater; only unverified factor is gas pressure.

  4. #4
    Join Date
    Sep 2007
    Location
    edmonds wa
    Posts
    4,434
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    Should get into habit of checking gas pressures in to and out of gas valves.
    UA Local 32 retired as of Jan 2020

  5. #5
    Join Date
    Jan 2009
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    Thread Starter
    thanks, buddy

  6. #6
    Join Date
    Aug 2002
    Location
    Cincinnati, Ohio
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    Somehow manufacturers don't believe airflow has anything to do with heat transfer. The fact of this situation is that the air is moving too fast and cannot remove heat from the heat exchanger therefore hot top, hot b-vent and low temp rise.
    captain CO

  7. #7
    Join Date
    Jan 2009
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    Thread Starter
    Quote Originally Posted by Jim Davis View Post
    Somehow manufacturers don't believe airflow has anything to do with heat transfer. The fact of this situation is that the air is moving too fast and cannot remove heat from the heat exchanger therefore hot top, hot b-vent and low temp rise.
    wow. Simple thermodynamics. My first instinct was to put some of the baffles back. I think what I'll do is bypass some air with a damper monkey around with the air flow and a temperature probe and see if I can get it coo

  8. #8
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    27,208
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    What “Baffels” did you remove?

  9. #9
    Join Date
    Jan 2009
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    11
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    Thread Starter
    i removed "finger baffles", per the installation manual.
    from factory, EEDU 300 maximum "throughput" was less than the 5,000-plus cfm my ahu is putting out. removing some or all baffles converts unit to higher cfm throughput

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