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  1. #1
    Join Date
    Jul 2007
    Location
    Oklahoma
    Posts
    3

    Confused Black dust/particles in duct work...

    Heat pump system with strips, no gas. The black particles are in both plenums. White insulation. Silver flex. House is 10 years old. The particles are coming out of the air vents and coating the ceilings and walls. Any ideas?

  2. #2
    Join Date
    Mar 2005
    Posts
    997
    Sounds like the linner is breaking down! Have it coated with something like Foster 40-20

  3. #3
    Are you sure the particles are coming out of the air vents? A fairly common mistake people make is to think the build-up of dirt on the ceiling next to a supply register is from the HVAC system. In actual fact that dirt is from the room. It builds-up there because of the effects of airflow.

    The dirt you see on the walls and ceiling could very well be coming from a source inside the room. For example, candle burning can cause this phenomenon.

  4. #4
    Join Date
    Dec 2007
    Posts
    18
    Quote Originally Posted by breathe easy View Post
    Are you sure the particles are coming out of the air vents? A fairly common mistake people make is to think the build-up of dirt on the ceiling next to a supply register is from the HVAC system. In actual fact that dirt is from the room. It builds-up there because of the effects of airflow.

    The dirt you see on the walls and ceiling could very well be coming from a source inside the room. For example, candle burning can cause this phenomenon.
    It can also come from the attic. If the installer didn't seal around the boot when it was cut into the sheetrock it can draw dirt and dust from the attic when the fan is running .

  5. #5
    Sure, it could come from the attic. As Mark B. keeps emphasizing proper sealing of the HVAC system is one of the most important things one can do for indoor air quality. The dust could also come from the HVAC system itself.

    But it has been my experience that when someone sees black dust on walls and ceilings it usually does not come from either. It usually comes from inside the room. Here is a way to prove it to yourself. All you need is a "windmill" type anemometer and a source of steady air flow. I use a small air purifier when I demonstrate this. Put the anemometer next to, but not in, the airstream. You will see that the "windmill" actually moves counter-clockwise. In other words the air is actually moving TOWARD the source of the airstream. Now move it into the airflow. The "windmill" will reverse direction and move clockwise. This effect sucks airborne dust in the room to the ceiling right next to the supply air duct.

  6. #6
    Join Date
    Jun 2007
    Location
    Logansport, IN
    Posts
    20
    This may sound really out there, but I had a customer who had a similair problem. I sealed everything in the duct system, even taped filter door shut and I went back and checked in two weeks. Same black stuff. Turned out to be from candles. She would let the wicks get long and they smoked and the returns would pick up the smoke and blow it out the the vents. The filter didn't stop the black particals. Might be something to check.

  7. #7
    Join Date
    Apr 2005
    Location
    new jersey
    Posts
    752
    Quote Originally Posted by Kev-Bo View Post
    This may sound really out there, but I had a customer who had a similair problem. I sealed everything in the duct system, even taped filter door shut and I went back and checked in two weeks. Same black stuff. Turned out to be from candles. She would let the wicks get long and they smoked and the returns would pick up the smoke and blow it out the the vents. The filter didn't stop the black particals. Might be something to check.
    I had a homeowner who moved into her new house and started getting black stuff all over the place .she threatened the builder and wanted the ducts cleaned. I went in to investigate and noticed it on the return grills,caked inside the filter, and looked around to find lots of candles. I asked if she likes candles and was like I love them and use them every night. I told here this was the black soot problem and she kind of got red faced. Once you see it the first time it is very obevious to trouble shoot

  8. #8
    Join Date
    Jul 2007
    Location
    Oklahoma
    Posts
    3

    thanks

    I have an appt with the customer tomorrow, so we will see about the candle situation. But on the sealing point we did a duct cleaning and sealed all the boots to the ceilings to prevent infiltration from the attic. The duct work was zipped and taped and doubled checked so I don't believe it is coming from the attic. We took a torch to the white insulation to see if the heat strips was burning it into that black dust but the insulation didn't do anything just sat there, good stuff. Now question on the candle residue is it soot, like out of the fireplace?

  9. #9
    The word "soot" is like the word "dust." It can mean lots of things.

    But generally both soot from a candle and soot from the fireplace are the same in that they are both carbon based and dark in color.

    Good luck with your customer.

  10. #10
    Join Date
    Jun 2005
    Location
    The Gray Northwest
    Posts
    661
    I think breathe-easy hit the nail on the head. I am constantly called out to sites with "bad air" because the diffussers are black (diesel repair shops). They don't believe me when I tell them it ain't from the duct work. Also, the velocity of the air moving through the diffusser creates a static charge that will attract and hold airborne particulate generated in the space.

  11. #11
    Join Date
    Jul 2007
    Location
    Oklahoma
    Posts
    3

    Found it.

    We found a hole in one of the return air boxes and I found that by the white insulation turning black. So in closing it was attic air. Its hard to see everything but I am going to talk to the duct cleaning crew. Thanks for all the input.

  12. #12
    Join Date
    Apr 2007
    Posts
    38
    An RSES Journal some time ago said that the black soot is from candles. If I ever get the time and gumption I may look it up if your interested.

  13. #13
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,210

    candles

    Yes, I agree, candles are one of the worst offenders for giving off black soot. People should never use parrafin wax ony Bees wax candles.

    thorton
    ____________________
    Don't be irreplaceable! If you can't be replaced, you can't be promoted.
    We have first to recognize that we are dispensable, before we can become truly indispensable

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