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lbelle5_gw

black dirt from vents

lbelle5
11 years ago

I just moved into a 50 year old home. There was a new heating unit put in 7 years ago. An addition was put on in 2004.

Once the old owners moved out, you could easily see where black dirt was sucked into the vents as well as where the vents put out the heat/AC onto the walls. Some areas worse than others.

I was thinking I just needed the ducts cleaned, but after reading up on it, I don't see anyone mentioning being able to see obvious dirt on walls or carpets. It's almost as if someone used a kerosene heater with black oily smoke. There was no mention of a fire at any time in the disclosure.

Any ideas what it is from? Or if duct cleaning is sufficient? Hate to disturb any asbestos like product that may have settled in over the years of remodeling in this house.

Comments (11)

  • energy_rater_la
    11 years ago

    post some pics
    its hard to see from here

  • RobbZee
    11 years ago

    Wow, I would call an HVAC guy in to take a look. You don't want to use it without getting it checked out first. It could be something serious and not just dirt.

  • lbelle5
    Original Author
    11 years ago

    Can't post pics as carpets got cleaned as did the walls. It wasn't horribly black like a fire, nor is it obvious coming out of the vent. however, I think getting an Hvac guy in might help. I have noticed that the unit has been checked spring and fall religiously according to the sticker on the unit. That's why I'm thinking it's something icky in the ducts...
    The carpet cleaner suggested the house needed more venting? Too much negative pressure ore something like that? Odd part is that it's from the intake and output vents

  • brickeyee
    11 years ago

    Burning candles for long enough will throw smoke stains, and HVAC filters are not fine enough to catch the particles.

    It could also just be from long term coking without
    adequate ventilation (or not running the vent fan if it is noisy).

    Clean and paint before spending money on duct cleaning.

    If the marks start to return THEN take additional action.

  • energy_rater_la
    11 years ago

    if a room is starved for return air it will put
    the room under a negative pressure. the room will
    then suck air from where ever it can get it..
    under sole plates of exterior walls is common if
    they were not sealed during construction.

    as the air is sucked thru the gap it brings dirt
    particles with it, causing dark marks on the carpet.
    for example a master bedroom/bath suite with 2 supplies
    in bedroom, one in bath, one in each closet with
    door to hallway undercut 1" will have a dark mark
    under the door to hallway.

    air is being supplied with insufficient pathway for it
    to get back to return grill.
    if homeowners keep the doors open, its not a problem.
    but when the bedroom door is closed, the 1" undercut
    door only returns for 1 supply. this is why jump ducts
    and transfer grills are installed. to provide
    a dedicated pathway for air to get back to return.

    the dark marks are called ghosting. hvac folk will tell
    you it is because of burning candles...but it is really
    a symptom of not enough return air.

    dirt marks on supply grills are from dirt.
    if you remove the supply grill you will see that the
    cut in the sheetrock is not sealed where the supply box
    is attached. the air is pushed out of the supply box
    when unit is running. dirt from the gap around the supply
    box is also picked up and pushed out.
    if condensation forms, the dirt sticks to the condensation
    and grills are dirty.

    take a look by removing a supply grill.
    post back or show how it looks.
    we can help you fix it if we know how it looks.

    include the following information.
    size of unit, size of return (on filter)
    location of return, location of heating system.
    type of ducts.

    best of luck.

  • sschoenberg44
    7 years ago

    We had a furnace fire last February. Finally got back in home in September, replaced furnace with new Heat Pump. Two months later I saw black stripes under back bedroom doors. I later lifted a 8x10 rug I have over our NEW Ivory carpet and saw the underneath was fine but around the edges quite a ways out is now gray. I keep reading it's from candles but we have lived here for 20 years and have never seen this happen. I have always had a candle going off and on during the holidays just like this year. Why is this happening ?

  • energy_rater_la
    7 years ago

    do you keep the doors to these rooms closed?

    where is nearest return air in relation to these rooms?

    from my 5 year old reply to op:

    "air is being supplied with insufficient pathway for it
    to get back to return grill.
    if homeowners keep the doors open, its not a problem.
    but when the bedroom door is closed, the 1" undercut
    door only returns for 1 supply. this is why jump ducts
    and transfer grills are installed. to provide
    a dedicated pathway for air to get back to return.

    the dark marks are called ghosting. hvac folk will tell
    you it is because of burning candles...but it is really
    a symptom of not enough return air."


    best of luck

  • klem1
    7 years ago

    I agree things pointed out by rater should be checked but imo insufficient filtration is the larger problem. I normally recommend 1" pleated filters for average homes. Anytime there's a fire,flood or extensive structural damage,I highly recommend 4" pleated filter(s). If you decide to retrofit with 4" filter(s),have them install over sized because they cost the same but offer extended change intervals. For the present you should install quality pleated paper filters to see if they catch black particles.

  • energy_rater_la
    7 years ago

    1" pleated filters are very restrictive.

    measure the air flow difference between 1" and 4" filters and you'd

    be surprised at the difference.

    either 4" filters with 1" lip that fits into existing return air filter grill, or modify/replace r/a fg with one that holds the 4" filter. the former is expensive in filter costs, the latter a one time charge to accommodate the 4" filter & much cheaper cost of case of pleated filters.


    best of luck

  • klem1
    7 years ago

    "1" pleated filters are very restrictive."

    I respect your expertise in your field of which ventilation and filtration are an important consideration but urge you to reconsider that statement. To say that is akin to saying window screen is very restrictive. While that is true,window screen is ideal for where it's used. On the other hand many engines have overheated because motorists placed window screen on their radiator to exclude bugs. I summit a generously sized 1" filter can be more than sufficient and not deterimental to system performance. The harm in saying 1 inch filters are restrictive is that homeowners and rookie techs might except it as absolute and throw in cheesy fiberglass filters. The coils will shortly be coated in dirt and lint that is far more restrictive than any filter would ever be. I agree 4" filters are great but the reality is too few contractors install them so we are left to stir homeowners in the best direction under the circumstances. You will do yourself a real service by working with a hvac contractor some time with right tools to determine when air flow begin's to effect overall system performance. Multiple things must be monitored, such as pressures,amp draws,temperature drop/gain across coils before drawing a conclusion. The fact air cfm begin's to drop does not mean system performance is suffering. I don't just think air flow and filtration are misunderstood,decades of experience confirm's that it is GROSSLY misunderstood (not that I understand it completly,but I openly admit all he time that I'm a student). Thanks for hearing my opinion,I always value yours.

  • energy_rater_la
    7 years ago

    NIce post Klem, sorry I missed it until now.

    this is the latest, albeit not the only discussion of 1" pleated filters

    on the pro hvac site. to answer homeowner questions one must

    be pro member.

    http://hvac-talk.com/vbb/showthread.php?2036981-quot-Premium-quot-Air-Filters-Reduce-Air-Flow

    granted 90% of the pro members there are there to offer the best

    itrw advice, and we are not the low bid companies in our areas.most techs have no concept of air flow other than to change

    dip switch settings.


    my post reflects my experience, my personal testing of different filters

    and the results of other hvac pros who have done the same.

    lately I have had limited time to post and surely

    omit details I should have included.


    keep up the good advice you provide to homeowners here.

    sincerely.