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  1. #1
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    Default Excessive soot: LPG

    Today's inspection revealed a set of gas logs in a prefab fireplace unit. There was excessive soot on the top logs and the damper and the chimney entrance.

    They were using LP gas.

    What is causing the excessive soot?

    Bob Harper - are you out there?

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  2. #2
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    Default Re: Excessive soot: LPG

    Looks like poor drafting. Check to see if the termination components are all listed by the manufacture. Are they burning with the doors half open, closed, fully open? Manufacture may spec that too. Is there a combustion air vent?

    Last edited by Marc M; 02-15-2010 at 08:37 PM.
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  3. #3
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    Default Re: Excessive soot: LPG

    Improper fuel to air mixture. Might be the air shutter adjustment, log placement, or just a spider in the equipment. The more yellow the flame (for looks) the worse the fuel / air mix. Proper blue flame resulting from correct air / fuel mixture does not impress the wife. Looks like they went a little overboard though.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  4. #4
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    Default Re: Excessive soot: LPG

    That's what I'm thinking, but for a different reason. Would this be caused by the wrong orifice on the gas log set? Natural gas vs. LP

    Bruce Thompson, Lic. #9199
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    Home Inspections in the Tyler and East Texas area

  5. #5
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    Default Re: Excessive soot: LPG

    Quote Originally Posted by JB Thompson View Post
    That's what I'm thinking, but for a different reason. Would this be caused by the wrong orifice on the gas log set? Natural gas vs. LP
    I see it all the time in Natural gas units that are not likely to have had any conversions. Did you see the flame? Bright yellow or lazy dark blue?
    Let's see if I can remember the right direction on Propane vs Nat. Gas; propane gets a smaller orifice so that would yield an over rich condition if Nat. Gas orifice was left in a propane application if all other things were equal which would appear to be a dark blue lazy flame. Bob?

    Jim Luttrall
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  6. #6
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    Question Excessive soot or relatively normal?

    Ok, looks like we have vented gas logs installed into a factory built fireplace. If ventfree logs, Houston, we have a problem....

    Let me ask you: if the gas logs were removed how would you feel about having all that soot in the firebox, damper, and chimney flue?

    Those logs do appear to be out of position, which in and of itself, it can cause sooting. There are a lot of other things that can cause it but this is not one to armchair quarterback on.

    Bob

    Keep the fire in the fireplace.

  7. #7
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    Exclamation gas log errata

    LP=small orifices; NG=larger

    If you left a unit set up for NG but fired it with LPG, it would Vesuvisize and possibly burn the house down. The opposite would result in a weak pilot flame that kept dropping out and a very small burner flame.

    The flame color may not change as much as you'd think. The more gas you blow through an orifice into the mixer tube the more air is entrained through the air shutter( venturi). Also, LPG entrains more primary air than NG at a given volume.

    Typically, high primary aeration results in short, intense blue flames; low primary air typically results in tall, lazy yellow flames. The hearth industry tries for blue bases with yellow tips.

    Now, a low manifold pressure can result in short yellow flames that impinge on the logs causing sooting. High manifold pressure can result in flame impingement, too depending upon log position. High primary aeration blows more air/ fuel through the burner resulting in stronger flames. High secondary airflows such as with open hearth fireplaces result in cooling the flames thus causing some sooting.

    These logs appear to be ceramic/ refractory logs, which are expected to soot up some. Ceramic fiber logs tend not to soot but can. Mfrs. generally show a basic log position plan for ceramic logs but allow some repositioning, esp. to minimize flame impingement. Ceramic fiber logs usually have some sort of indexing such as pins or flat spots or are screwed together but usually odn't soot.


    These are just a few causes.
    HTH,
    Bob

    Keep the fire in the fireplace.

  8. #8
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    Default Re: Excessive soot: LPG

    flame seemed to be normal looking

    so, you're saying that there could be several reasons for the sooting - but that it's difficult to determine over cyberspace photos ?

    Bruce Thompson, Lic. #9199
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    Home Inspections in the Tyler and East Texas area

  9. #9
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    Question mo pics?

    Quote Originally Posted by JB Thompson View Post
    flame seemed to be normal looking

    so, you're saying that there could be several reasons for the sooting - but that it's difficult to determine over cyberspace photos ?
    Any pics further back showing the entire burner and logset?

    Keep the fire in the fireplace.

  10. #10
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    Default Re: Excessive soot: LPG

    no, just those two. Sorry.

    thanks for the help

    Bruce Thompson, Lic. #9199
    www.TylerHomeInspector.com
    Home Inspections in the Tyler and East Texas area

  11. #11
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    Default Re: mo pics?

    Quote Originally Posted by Bob Harper View Post
    Any pics further back showing the entire burner and logset?
    Thanks, Bob. Now can you do an armchair analysis of this one? He's on the 5th floor there.
    Is this far enough back?

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  12. #12
    Rob Yarboro's Avatar
    Rob Yarboro Guest

    Default Re: Excessive soot: LPG

    I'll armchair this one......sooting problem that needs to be addressed by a professional.


  13. #13
    David Bell's Avatar
    David Bell Guest

    Default Re: Excessive soot: LPG

    Check gas valve for NG or LP stickers, conversion requires labeling. Also check for blockage of orifices.


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