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Why is the main floor of my house covered in soot?

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The main floor of my ranch style home is covered in soot. I have base board heating, instant hot water and a wood burning fireplace. My furnace has been checked and I did not have a puff back or a cracked heat exchanger. I have had every professional out here to check my home and no one can figure out the source. Please help!
asked in Interior Walls by hcklimkosky (120 points)
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1 Answer

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Hi there,

I'm not sure smiley... could you tell me:

  1. what's underneath the floor (basement, crawlspace, concrete slab), if basement or crawlspace - do they have finished ceiling, if crawlspace - does it have a finished floor?
  2. what's on the floor (carpeting, hardood, tile)?
  3. did anyone checked fireplace chimney?
  4. was the chimney recently cleaned?
  5. is there a functional damper in the fireplace chimney?
  6. is the soot something recent, maybe associated with some changes inside your home... remodeling?
  7. how are your appliances vented, how many chimney's / flues there are?
  8. oil or gas burning appliances, where are they located?
  9. are you absolutely sure this is soot, is it only visible on the floor surface / nothing on walls or ceiling.

Please explain in as much detail as you can, just click "comment" below


answered by darekrudy (21,730 points)
Thanks for responding! I have a finished basement with carpeting and a drop ceiling. I have carpeting in the living room and bedrooms, hardwood in the kitchen and tile in the bathrooms. Yes, the chimney has been inspected and cleaned after I noticed the soot damage. Yes, I have a damper that is closed for the most part as I only have an occasional fire. I finished the basement 1 1/2 years ago. No other remodeling. We have electric stove. Two (metal) chimneys, one for the fireplace and one for the furnace. I have an oil burning furnace. It is located in my laundry room in the basement. It is absolutely soot. It is everywhere. Most noticeable on exterior wall, cathedral celings. You can see soot in every room in the main floor, walls, ceilings and floors. It's even noticeable on shades and ghosting marks around pictures.
Just wanted to mention that my furnace is in my laundry room (in the basement) which is approximately 12 x 20 with an unfinished ceiling. We also had the furnace checked and the draft/ air flow being exhausted through the chimney tested normal. Efficiency tests on furnace came back at reccomended levels.


Hi Heather,
From your description everything points towards the furnace. I understand that it was already evaluated by a professional but… instead of trying to explain the basics let me just quote Wikipedia:
Soot, as an airborne contaminant in the environment has many different sources but they are all the result of some form of pyrolysis. They include soot from coal burning, internal combustion engines, power plant boilers, hog-fuel boilers, ship boilers, central steam heat boilers, waste incineration, local field burning, house fires, forest fires, fireplaces, furnaces, etc. 
These exterior sources also contribute to the indoor environment sources such as smoking of plant matter, cooking, oil lamps, candles, quartz/halogen bulbs with settled dust, fireplaces, defective furnaces, etc. Soot in very low concentrations is capable of darkening surfaces or making particle agglomerates, such as those from ventilation systems, appear black.
Soot is the primary cause of "ghosting", the discoloration of walls and ceilings or walls and flooring where they meet. It is generally responsible for the discoloration of the walls above baseboard electric heating units and can be known as a gas.
Your exterior walls and cathedral ceilings are colder than the interior surfaces: that’s why stains are more significant there. As stated above, the only way to get soot in your house is by burning something inside or by allowing soot particles from exterior. It has to be one of those two, there’s really no other way… you need to go item by item and consider each one of them as a possible source.
One more thing, take a look at this post about combustion air and make sure there’s enough of it in the furnace room, hopefully you have a carbon monoxide alarm installed as well.