Source of Black Soot and Musty Smell in House?

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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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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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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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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