Finding the Source of Black Soot in a House?

November 4, 2015

We suddenly found black soot like powder on the floor, walls, baseboards, and furniture about 3 weeks ago when dusting. We attributed it to the furnace though we have no vents since we have in floor radiant heat, or the fireplace, which had just been cleaned. We also then had the furnace cleaned. About a week later, we noticed a slight musty smell which has since intensified. The smell is in the same area of the house but strangely also upstairs on the opposite side of the house in a bedroom. Airing out the house helped, but the smell immediately intensifies when the windows are closed.


Initially, we did not associate the two, thinking the smell may be from a dead mouse in the wall. We are still searching. During the search, we have found the soot again even though we have not used the fireplace. The black powder is on the baseboard and the windowsill of the half round windows above the lower casement windows. The lower sills do not have the powder. What can this be? Are the two issues related or do we have two separate problems? We would appreciate any insight or information about similar experiences. Also, I would gladly call a professional, but I don't know who to call.


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November 5, 20150 found this helpful

This is a puzzle. Soot must come from somewhere where there is combustion. If you have in floor heating, (water pipes in the floor, right?) you must have a boiler. Does your boiler run on natural gas? Perhaps there is some problem with that, although how soot would get all over the house is beyond me. I have a natural gas boiler for hot water heat (radiators) and I had to have the burner replaced, because it was producing a sooty mess, but only inside the furnace.


However, I would call someone about the furnace first. I would suspect that if your boiler burns some other fuel, it would be even more likely to produce the soot. If that is not the problem, could the soot have gotten all over when the fireplace was cleaned?

I would not worry about the smell until after I had the furnace dealt with. They may be the same problem. If not, I think that you might be on the right track with the mouse search.

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November 6, 20150 found this helpful

Could what you think is soot really be mold? That would give your house a musty smell.

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May 20, 20190 found this helpful

The appliances are doing what they are supposed to do, but there's still soot and dirt. In fact, the soot is oozing out of attic vents, through attic hatchway doors, and into and out of vents. Is this the mystery?


No mystery, but a phenomenon with a rather sinister-sounding name: depressurization combustion re-entry.

A mouthful, maybe, but easily explained.

What happens: In a house that is well insulated and nearly airtight, the air pressure is lower indoors than out because air movers (dryers and exhaust fans, for example) are pushing air out of the house, and the house is too tight for new air to come in to balance off the pressure. Or, wind on one side of the house is pulling out the air, a venturi effect.

This happens often in new, tight houses. By itself, it is not a bad thing. But what happens is that the house wants to bring in air to even out the air pressure; trying to inhale, as it were.

If the outside air is clean, there is no problem. But if the outside air is contaminated, that contamination will get into the house. Yes, but how does that outside air get contaminated?


Sometimes a power vent (a burner or stove vent that does not need a chimney) that goes through the wall will contaminate the air, which is then drawn into the attic through the soffit vents.

Sometimes a low chimney, one that is not higher than the roof ridge, will not exhaust smoke and particles high enough, and instead waft smoke and particles into the attic by way of the ridge vent.

Or, particles will follow the vent stack into the attic, and land on the attic insulation. Dirty insulation is a sure sign of this.

Preposterous? Not at all, although you may have to be a physicist or engineer to understand it entirely.

Take an engineer's word for it. It does happen.

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January 29, 20200 found this helpful

I think it might be coming from the exhaust from commercial jets. JP4 or 5 jet fuel. We live close to the air port and the exhaust from jet fuel has to go some where the atmospheric space.


When furnace or air comes on. It sucks in through furnace.

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April 25, 20200 found this helpful

I had run in an apartment which is actually a house that has an upstairs apartment which I am in and a downstairs since I've been here to tenants have moved out of the apartment below me I have been here for almost four years and it took up until last year to notice how bad it is literally you cannot put anything in the cupboards 24 hours it's covered in Black in the refrigerator Solo cups left out within two days even stacked inside covered with black I have to throw away and all furniture I recently well actually two days ago I found out by walking into the empty apartment because the tenant had just moved out that he has nothing to do with me because it's the it's the same way right when you walk into the apartment the walls fully are covered in black soot and it's all over the counters and everything every single thing that enter this apartment I guess the black soot within 2 days there's no escaping it I'm here 24 hours a day 7 days a week I don't leave for work I work here. I've been working on person I have been breathing this stuff in you know just discovering that I have been a year ago I was I was just so shocked to know that I can't even Escape it by putting every single thing that's edible in the refrigerator or freezer because it's there two pots pans in the cupboards in the kitchen I mean clothes that need washed you know if it takes a week to get to the laundry I mean it's everything is covered realizing that every time I even took a drink before I noticed what was going on how I noticed was I went to use a cup that I just actually took out of the package and I was putting ice in it and the whole inside was just black and I'm like I just could not understand what was going on I threw them all away and it just kept getting even worse I thought putting even the plastic cups and plastic plates and everything in the refrigerator would protect them boy was I wrong I have had extreme health issues regarding my breathing heart palpitations and swearing that it's on my contact lenses because since I've moved in here I mean literally what a mess it has affected so much I am on a mission during this coronavirus pandemic unfortunately to hurry up and make sure I get out of here ASAP coming to the realization of realizing that everything gets covered that I am breathing the stuff in and I obviously somehow this has to be the cause of what has been Total Health nightmare for me I don't know how to tell if for doctors to know if you know it's in my system I don't know how it cannot be I will be finding out

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May 4, 20200 found this helpful

Can I ask what you would do to correct in?

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Ask a QuestionHere are the questions asked by community members. Read on to see the answers provided by the ThriftyFun community or ask a new question.

February 17, 2020

I have black soot in my apartment that is sticking to mostly plastic items, cups, plates, trash cans, even in my bathroom sink and toilet seat. The maintenance department is stumped and my property manager keeps blaming it on candles. (I burn maybe one candle once in a while if I'm feeling crazy 2). Source of Black Soot Sticking to All Plastic Items in Apartment


I haven't been staying there since I woke up and blew black soot of out of my nose.

The property manager says there is no gas leak, no filters to change. I mentioned a boiler backfire and she said it's not possible since the boiler is not gas fired forced air. Anyone know where this can be coming from and what I should do to make sure it's repaired and finished? I just want to go back home!

Source of Black Soot Sticking to All Plastic Items in Apartment
Source of Black Soot Sticking to All Plastic Items in Apartment
Source of Black Soot Sticking to All Plastic Items in Apartment
Source of Black Soot Sticking to All Plastic Items in Apartment
Source of Black Soot Sticking to All Plastic Items in Apartment
Source of Black Soot Sticking to All Plastic Items in Apartment


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February 17, 20200 found this helpful

Do you have a local health department or a mold remediation company that can swab the stains and culture them or an independent home/building inspector? I would contact a neutral third party to investigate.


Post back with an update! Prayers for solutions.

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February 18, 20200 found this helpful

I feel that there is damp/moisture through out this location, which is looking like mold. I'm assuming you do not have a fire place with poor ventilation/flew that would send build up throughout the space. This is not something to let go, either way this could cause many other issues. Have a professional check it out!

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February 18, 20200 found this helpful

That is horrible and this is dangerous to your health. If you blew this out of your nose one morning I would say it is not mold but something else. I would contact a company who could inspect your apartment and actually determine what is going on. it sounds like this is something that just started happening at your home. It also sounds like the landlord is not willing to try and help out. I would call the health inspector and also a company who deals with soot or mold to check out your aprartment and determine where the stuff is coming from.

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February 19, 20200 found this helpful

It sounds as if it is growing mold somewhere.,in your house.What type of heat do you have?It could be your heating source giving off blac soot.

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February 21, 20200 found this helpful

I rented a twin house and had a similar problem. I found out that the attached neighbor was using a kerosene heater that apparently was not maintained properly that caused it to smoke excessively.

Being the houses were old and we shared a main wall, the soot was coming through small cracks around the flooring and baseboards from their house. I did ask them and they were using the heater, they did stop and so did the soot problem.

Also, when burning any candle, be sure to keep the wick trimmed. Normally the information about how much to keep trimmed and how long it should burn will be on the bottom of the candle. This can also cause a soot problem.

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January 8, 20220 found this helpful

This happened to me. I searched everywhere for the source: changed furnace filter, checked to make sure vents werent blocked, emptied central vacuum...still nothing. Turns out my wife bought a new candle and it was letting off black smoke. Wives, am I right...!!!

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March 10, 20220 found this helpful

i am currently going through this right now, its all over my trash can, my bowls cups and plates (but my cabinet stays closed so idk how it gets on there) on my fridge, its just all over the place and its soo irritating, i meet up with my "landlord" today so fingers crossed!

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April 8, 20220 found this helpful

This happened to me about a year ago and I ended up getting charged for damage to the walls by my landlord because it was all over the walls he claimed that I had been smoking in the apartment but I never smoked or even lit any candles. I had a wax burner that I would turn on maybe once a month. Never ended up finding out the source.

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