Why is black soot coming from my electric heating vents?

electric heating

We have two AC/heating systems. One is fine, the other (over time of 2 months) has a black sooty residue collecting where the air blows out. This unit has the vents in the ceiling. Will filters help? Where should they go? In the return or in the room vents?

The soot seems to be in the air because if I close the bedroom door closest to the heating unit, the black soot gets on the carpet under the door.
There is a 20×20 filter in the return……as it should be, but the soot collects anyway. I even tried one of those Arm & Hammer ones that are suppose to trap allergens and more dust than the spun fiberglass ones. I couldn’t tell that it did any better.

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4 Responses to “Why is black soot coming from my electric heating vents?”

  1. rlbendele1 Says:

    Its not soot its mold. Mine did this after the ac unit was replaced with a new effecient unit. The installer had put in a new micro filter. Once the filter was changed back to a normal "cheap" filter the problem stopped. It took the ac cmpany 9 months of coming out 2 to 3 times a month to find the problem. Once the regular filter was installed the problem got better in a week or so.

  2. LindseyAG Says:

    you definitly need a filter. In my HVAC system, my filter goes in my furnace which is hidden in my garage.

    Edit since you added further info:

    You need to clean out your ducts. This is fairly inexpensive (depending on the size of your house and how many returns and vents you have) I would call around to HVAC companies in your area and get some quotes. I did this last year and it was under $200 on a 3 level 1500 sq ft home(it is a good idea to do this annually anyway to keep heating and cooling costs down)

  3. Soccer Coach Says:

    It needs to have a good cleaning.


  4. Stephanie Says:

    Do you burn candles on the side of the house that has the black soot? I used to burn candles all the time because I enjoyed the way they smelled. Then I started noticing black marks around the ceiling vents and also UNDER THE CLOSET DOORS as you mentioned. It has to do with the way air circulates in your house, and the candle soot is more likely to get trapped in the carpet fibers under closed doors. It also collects more under windows. Check your carpet under the windows to see if you have grayish black stains along the edge of the carpet next to the wall. Another way to check for candle soot is to wash the interiors of the windows on the affected side of the house. Do your paper towels get black? If so, and if you have been burning candles, you definitely are dealing with candle soot. Another test is taking a picture off a wall to see if there is a “ghost” stain around it.

    Do a search using the words “candle soot” and you will find many sources that describe the phenomenon. Here are two to get you started.


    If it is candle soot, there isn’t a filter on the market that is capable of trapping these tiny soot particles. Also, so-called “duct cleaning” companies cannot clean the soot that is deposited inside your ducts. They can clear out dust, but not soot. Believe me, I have tried both remedies. Its been years since I burned a candle in our house, but we still have a minor soot problem from the deposits that are stuck inside the ductwork.

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