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Thread: Vent Damper

  1. #1
    Join Date
    Mar 2007
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    Ridgewood, NJ
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    237

    Default Vent Damper

    I've been seeing a lot of those old style bi-metal vent dampers recently. Some old ones reinstalled on new heating systems with atmospheric venting. Usually the venting is marginal when these are in use. I've seen some that barely open at all.

    Are the bi-metal dampers still manufactured, and can they still be installed?

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  2. #2
    Join Date
    May 2007
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    Frankfort, KY
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    Default Re: Vent Damper

    Never understood why a restriction is knowingly placed in the flue.

    It would serve the appliance & venting system much better to have a double acting barometric installed.

    Take the draft hood & vent damper completely out, they will cause nothing but trouble.

    Measured Performance more than just a buzzword

  3. #3
    Join Date
    Mar 2007
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    Near Philly, Pa.
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    Cool danged Vent Dampers

    If you are talking about Ameri-Therms, they were sued and these unit pulled off the market. They have four valve leaflets, much like a heart valve except they are bimetal. As the unit fires, the heat causes the leaflets to open (hopefully) allowing some flue gases to pass. Some don't. Take a look at these pics of a 3" and 4". Note how the leaflets still posed considerable turbulence to the flue even when opened (here, I'm using my pen). Sometimes the leaflets would hang up and fail to open. Others, the rivet would fall out (as seen here) and snag.

    The IFGC 503.14 simply requires all vent dampers be listed. They do not exclude bimetal or mechanical types. It also does not specifically name ANSI Z21.68 as the listing which applies nor does it come out and require any sort of safety interlock or spill switch. Most electric automatic vent dampers are interlocked to the gas control. On a call for heat, the damper must open first. Some actually have a microswitch to prove it is wide open. Next, the unit either fires or goes into a pre-purge then fires. Standing guard is a solitary spill switch. When the thermostat is satisfied, the burner cycles off. Some units then post-purge. Once purging is complete, the vent damper closes so as to minimize standby losses and dilution air up the stack. This boosts the unit's overall efficiency rating (AFUE).

    Another peril with these dampers is they are seldom screwed in. Being made of heavy stainless steel, it is hard to drill through with Zip screws so often, they can easily fall apart.

    If you need a code reference in shooting down this brand of vent damper, simply look at the label I showed you. Do you see a listing mark? That AGA mark is a design certification--not a listing mark from a recognized testing lab. Since these dampers are unlisted, they must go.

    HTH.
    Bob

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  4. #4
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    Mar 2007
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    Default Re: Vent Damper

    Added to my notes, thanks.


  5. #5
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    Default Re: Vent Damper

    Ran into one of these for the first time yesterday, I was wondering if anyone has a link to information about the lawsuit and removal of from the market mentioned it Bob Harper's post below. GOOGLE did not turn it up, and I'd like to be able to reference something definitive in the report ( beyond the listing issue that Bob cites).

    - Thanks

    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  6. #6
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    Default Re: Vent Damper

    Saw a nice example of spillage below an Ameri-Temp at yesterday's inspection:

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    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  7. #7
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    Default Re: Vent Damper

    And an even worse one today:

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    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  8. #8
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    Apr 2013
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    Michigan
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    Default Re: Vent Damper

    Quote Originally Posted by Michael Thomas View Post
    And an even worse one today:
    Thank you all. I've just puchased a house to find exhaust/heat pouring out of the furnace. Smelled just like a propane heater. It has one of these dampners on it and shows the same appearance (to a lessor extend) of the last photo. The fumes and heat were coming right from the vent areas shown in the last photo. Actually I believe the furnace is exactly the same as the last photo! No one is in the house yet (moving Sat.) and I've turned th heat down to 50 as it's still below freezing in MI. The post might have even saved us from major health problems. On behalf of my wife, four year old son and me, Thank you!


  9. #9
    Join Date
    Mar 2008
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    Charlotte NC
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    Default Re: Vent Damper

    Quote Originally Posted by Michael Thomas View Post
    Added to my notes, thanks.
    Mine too, thanks Bob. (By the way Bob, your pen has finger prints)

    The beatings will continue until morale has improved. mgt.

  10. #10
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    Aug 2011
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    Bennett (Denver metro), Colorado
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    Default Re: Vent Damper

    Quote Originally Posted by Michael Thomas View Post
    Saw a nice example of spillage below an Ameri-Temp at yesterday's inspection:
    Not to mention that particular version of Rheem's have reached the age where most have cracked heat exchangers, even if not leaking CO yet.

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