Photograph of  thermal tracking or soot tracking - cool surface, moisture condenses, soot is deposited - Daniel Friedman 02-12-16 HVAC Dust or Soot Stains
How to Diagnose Soot & Other Indoor Wall or Ceiling Stains Traced to Heating or Air Conditioning Equipment

  • STAINS HVAC SOOT or DUST - CONTENTS: Soot stains indoors caused by defective oil or gas fired heating equipment or debris stains caused by HVAC air movement. A photo-guide to heating systems as the source of some indoor ceiling and wall stains and what they mean - heating system trouble
  • POST a QUESTION or READ FAQs about wall or ceiling stains that are traced to heating system problems

This article describes & diagnoses heating equipment as the cause of various interior wall and ceiling stains and explains how to recognize thermal tracking, thermal bridging stains, building air leaks, and building insulation defects.

Often these stains are mistaken for toxic indoor mold. When investigating a building for a mold problem, you can save mold test costs by learning how to recognize Stuff that is Not Mold or is only Harmless Mold but may be mistaken for more serious contamination.

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Heating Systems & Other Sources of Dark Stains on Indoor Walls & Ceilings

Dirt at ceiling air supply register © Daniel FriedmanOur page top photo, sent by a reader, is a wonderful and unambiguous diagnostic photo.

We showed the photo at left also at Stains HVAC Supply Registers and discuss it further here.

Here's what we see that strongly suggests that the primary source of dark stains in this room is a problematic heating system:

  1. Black sooty stains are darkest right over the warm air supply register at the floor in the photo's lower right corner
  2. There are no stains or soot marks on the building walls where pictures have just been removed
  3. Black sooty stains are less dark on the wall surface as we move higher on the wall away from the heating register
  4. Black sooty stains on other walls in the room are much less noticeable

Dirt, Debris, Stains around Heating or Air Conditioning Air Registers

The soiling and "stains" around this ceiling supply register for warm air or air conditioned cool air show that the air system is dirty, has inadequate filtration, or is operating unsafely.

While mold or other problem particles could be present in this dirt or debris, if they are present they are coming from another source, not from this soiled area on the ceiling.

Here the debris deposited on the ceiling is in a common pattern where warm or cool air supply registers blow air across the ceiling surface (including from leaks around the perimeter of the register grille in this case.)

The stain pattern is from building air movement, it is not thermal tracking and it is not, by itself, an indicator of problem mold. A lab test of this debris for the presence of mold would not be justified based only on the observation of these stains, but it might be justified if there were other reasons to need to screen the building or its HVAC system for problem mold or other contaminants.

Also see Wall Thermal Tracking Stains for examples of thermal tracking above a heating baseboard, and see Stains HVAC Supply Registers for more discussion of this topic.

If you have frequent fireplace fires, cooking, or if you burn scented candles, if people smoke in your home, or if your oil-fired or gas-fired heating system is not working properly, the added soot particle load in the building air is not only a health concern (soot and potentially lead), it also will mark the building surfaces in this characteristic pattern.

We welcome more thermal tracking, soot tracking, air bypass leaks, and similar photos of indoor stains as well as text suggestions to expand this detail and would be glad to credit contributors.

Usually soot marks, thermal bridging, or thermal tracking stains appear, if at all, in the building interior locations discussed in the remaining sections of this article.

Readers should see HEAT LOSS in BUILDINGS.





Continue reading at THERMAL TRACKING BRIDGING GHOSTING or select a topic from the More Reading links or topic ARTICLE INDEX shown below.


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STAINS HVAC SOOT or DUST at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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