Photograph of  thermal tracking or soot tracking - cool surface, moisture condenses, soot is deposited - Daniel Friedman 02-12-16 How to Use Indoor Wall or Ceiling Stains to Diagnose Indoor Air Quality Problems

  • IAQ DIAGNOSIS via THERMAL TRACKING STAINS - CONTENTS: How to Use Indoor Wall or Ceiling Thermal Tracking & Other Indoor Stains to Diagnose Indoor Air Quality Problems. A photo-guide to indoor air quality issues that may be indicated by a several common indoor ceiling and wall stains and what they mean
  • POST a QUESTION or READ FAQs about how to use indoor stain patterns, locations, & contents to track down and correct indoor air quality issues
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

This article describes how to use indoor wall or ceiling thermal tracking & other indoor stains to diagnose building air leaks, missing insulation, and indoor air quality problem.

We also discuss other interior wall and ceiling stains, building air leaks, and building insulation defects. Often these stains are mistaken for toxic indoor mold. The black stains in the photo at page top are not mold, they were caused by candle soot from the two candle sconces shown in the image.

Green links show where you are. © Copyright 2017, All Rights Reserved.

How to Use Indoor Stains Like Thermal Tracking to Diagnose Building Air Leaks, Insulation Defects, and Indoor Air Quality Problems

Moldy carpet stains © Daniel Friedman

Significance of Other Indoor Stains and Marks for Building Framing Location or Defects in Heating & Cooling System Operation

The short explanation: thermal tracking and soot stains are not mold. But indoor stains may still indicate indoor health or air quality problems.

Many building stains, thermal tracking, thermal bridging, ghosting, stains at heating or air conditioning registers, and even mineral salts left behind by evaporating water at a foundation wall are all very easily recognized as "not mold". Review the stain patterns shown in these articles before ordering a costly building mold test or investigation.

While mold growth in buildings indeed follows the location of leaks or moisture, mold growth does not usually occur on building surfaces in the same regular pattern described by thermal tracking.

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. In addition to a study of the stain patterns of Thermal Tracking (this series of articles) readers should also see both  


Mold, Safety, & Health Warning:

Your building might have a separate mold problem:

However, because indoor moisture is an important factor in the cause of thermal tracking or soot ghosting, the same building that has lots of thermal tracking stains might also have a serious mold problem due to leaks, water entry, or high indoor moisture.

But where we find this to be the case, the location of the most serious building mold is often not at all the same as the location of the thermal tracking stains.

See MOLD / ENVIRONMENTAL EXPERT, HIRE ? for help in deciding when it is appropriate to hire a mold inspector.

Your building might have unsafe heating equipment:

both oil and gas fired equipment can produce soot when they are not working properly. Soot from a gas fired appliance is a very dangerous sign, often indicating that dangerous carbon monoxide (CO) gas is being produced - which can be fatal. Be sure your home has working smoke detectors and CO detectors.


Photograph of  thermal tracking or soot tracking - cool surface, moisture condenses, soot is deposited - Daniel Friedman 02-12-16This black stuff is not mold. Since thermal tracking, or soot marking, or "thermal bridging" always tell us about missing or openings in building insulation or about air leaks, we can learn other facts about a building such as those listed in this article on thermal tracking, soot stains, and other indoor building stains.

But don't assume that any stain on a building wall is due to poor insulation, moisture, mold, or thermal tracking. In the page top photograph we see candle soot - sometimes a source of indoor air quality complaints or even lead poisoning if a poor quality or perfumed candle is used to excess.

In the photo at left we see thermal tracking soot or house dust or cigarette smoke stains on a ceiling - but high building moisture that was a factor in this staining could also have been a factor in development of a mold problem somewhere in the home.

Indoor stains can also tell us of other conditions that should not be confused with mold or indoor air quality complaints:

How "Read" Indoor Stains to Identify Indoor Air Quality Concerns

A careful examination of the location of indoor stains permits the observer to use thermal tracking or soot marks on building walls or ceilings as an indicator of possible excessive (seasonal) interior moisture or other potential indoor air quality concerns.

Dark stains on building interior walls may appear in other patterns and could be from other causes - we provide photographs, description, diagnosis, and advice for many of these indoor stains in this article series. Let's start with another example
of THERMAL TRACKING BRIDGING GHOSTING so that we an distinguish these stains from others listed below.

Reader Question: These are some of the pictures from our living room.

( I mssgd yesterday about sending pic) it seems like this year its getting darker. My husb. went up to the attic and he does notice that insulation seems to need work but i want to make sure i have 2 small boys and everyone keeps saying it cant be healthy and now im worried. - K.C. 4/4/2014

Thermal tracking or ghosting stains on building ceilings (C) InspectApedia KC Thermal tracking or ghosting stains on building ceilings (C) InspectApedia KC

Reply: how to recognize thermal tracking or ghosting stains in buildings

Thermal tracking or ghosting stains on building ceilings (C) InspectApedia KCA competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. You will find additional depth and detail in articles at our website. That said I offer these comments:

There is no doubt that we are looking at thermal tracking or "ghosting" - deposits of dust and soot on cooler, more humid areas of ceilings in your home.

These are not themselves a particular health concern but the conditions that cause thermal tracking, if they involve high indoor moisture levels, particularly if that moisture comes from a damp or wet basement or crawl space, could be a subtle clue that there is a hidden mold problem in the building.

I emphasize that the stains themselves are not mold nor likely to be hazardous

We explain this phenomenon beginning

and we offer some remedies at THERMAL TRACKING REMEDIES.

An easy way to recognize thermal tracking (synonyms: ghosting, bridging, thermal bridging) is to notice where they appear and their patterns. These stains appear on ceilings below attics or cathedral ceilings and on exterior walls, and less often on interior partition walls that may suffer cooling from internal air movement or air leaks. The stains appear in rather regular and uniform streaks on intervals that map building ceiling joists or wall studs.

In some of youur photo details the shorter black ceiling stains between the longer ones (mapping ceiling joists) are perhaps areas of heat loss between gaps in the end butt-joints of poorly-laid ceiling insulation.

How to Diagnose Stains and Debris at Ceiling and Wall Heating or Cooling Air Supply Registers

Photograph of dirt on a ceiling at an HVAC supply register

Dirty HVAC duct work, lack of air filter maintenance, or furnace malfunctions can all be indicated by black stains that appear around warm or cool air delivery registers in building ceilings or walls. (This is usually a deposition of house dust, rarely is it mold, and rarely is it related to thermal tracking.

Details about these stains at registers are given at STAINS at HVAC REGISTERS

An investigation of what was at first called Killer House Dust from an HVAC system showed that the dust of concern turned out to be cotton and other carpet fibers having nothing to do with the Heating or Cooling equipment was discussed at our Fear of Mold WebLog or "Blog" where we periodically post results of interesting forensic investigations.

Fireplace smoke stains © Daniel Friedman

Indoor stains may identify unsafe heating equipment or poorly-functioning fireplaces: use thermal tracking marks on interior building walls and ceilings, particularly where they vary from room to room, to diagnose poorly-vented chimneys such as fireplaces that do not work well (also look for soot stains at the hearth face).

Such marks may also indicate poor and even unsafe operation of central heating systems since a poorly maintained oil burner will often leak soot into a building interior, and a dangerously un-vented gas appliance may also produce both soot and potentially fatal carbon monoxide gas.

And our photo at left shows a floor "stain" that tells us that the building could catch on fire due to an improperly-built fireplace: there is no hearth extension. An astute inspector would worry what other safety mistakes were made by this builder.

How to Recognize Pet Stains on Building Walls

Photograph of dirt from a pet smudging a wall

Evidence of pets in buildings: In buildings where pets are or have been housed, smudge marks on walls and at doors and door trim are sometimes mistaken for thermal tracking.

These are not thermal tracking, but these marks, along with others (scratches, urine stains) can tell us the history of pet occupancy in a building, information of use when investigating indoor air quality concerns, especially in spaces occupied by asthmatics or people with pet allergies.

Black marks on interior walls such as painted drywall might be just be where the dog lay on the floor against the wall (as shown in this photograph).

Notice that the stain patterns tend to be round or oblate, not mapping building framing nor HVAC duct air movement. Notice that the stain to the left of the oor is close to the floor by the door and that the same stain blotch extends to the the floor baseboard trim and the door jamb trim.


How to Recognize Wall Stains from Human Occupants

Black marks on interior walls such as painted drywall might be also be dark wall stains where people rested their heads [image] in bed (as shown in this photo).

Photograph of dirt from a pet smudging a wall

Look at the location of these stains and imagine a bed having been placed with its head against the wall shown in the photograph. Notice the two wall lights.

This is where a bed was almost certainly placed, and we can easily explain these black stains on the drywall. No further testing would be appropriate in normal circumstances.

How to Recognize Wall or Ceiling Stains due to use of Candles, Woodstoves, or Fireplaces

Photograph of candle soot smudging a wall Photograph of candle soot smudging a wall

Smokers or scented candle hazards: In buildings where occupants are or have been smokers, or where occupants burn candles, especially scented candles, thermal tracking will often be still more distinctly visible as soot stains in the thermal tracking patterns we've already discussed. Since scented candles can be a source of indoor air quality problems including toxic lead deposition and perfumes which are respiratory irritants to some people.

Thermal tracking on buildings combined with this evidence can also be a clue useful in diagnosing indoor air quality complaints. In these photographs, all of the stains visible appear due to use of candles. Note the absence of framing-interval staining (16" or 24" on center) which would have been characteristic of thermal tracking, even of the candle soot, had the building surfaces been cool due to poor insulation.

Excessive indoor humidity: If indoor humidity is too high we may be encouraging mold growth in a building or we may be inviting excessive levels of dust mite activity which in turn increases the level of allergens in the building.

Other Sources of Dark Stains on Indoor Walls & Ceilings

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.

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


Continue reading at AIR LEAK DETECTION TOOLS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.




Suggested citation for this web page

IAQ DIAGNOSIS via THERMAL TRACKING STAINS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman