Wall Stains & Thermal Tracking
How to Recognize & Diagnose Stains on Building Walls - Causes of High Heating Costs

How to Recognize & Diagnose Thermal Tracking, Soot Stains on Building Walls (and ceilings)
- Building stains can help diagnose the causes of high heating bills
- How to recognize poorly insulated building walls or ceilings and how to pinpoint building air leaks
- A photo-guide to common indoor ceiling and wall stains and what they mean
Questions & Answers about relating thermal tracking ghosting marks indoors to building insulation defects, air leaks, heat loss, and heating bills.
References

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Heating cost too high? Thermal tracking or ghosting stains may indicate the reason. This article describes How to Recognize & Diagnose Thermal Tracking, Soot Stains on Building Walls - Diagnosing Causes of High Heating Costs and discusses other 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.

How Air Leaks Cause Thermal Tracking or "Ghosting" Stains on Building Walls & Ceilings

Thermal bridging or thermal tracking soot stains on interior walls (C) Daniel Friedman

The black marks or stains or "sooting" observed in a characteristic pattern on building walls or ceilings are comprised of substances that cause black sooty marks on building interior ceilings or walls and sometimes also on carpets are from sources and causes that you can easily learn to recognize in buildings. Indoor air contains dust particles, whether you see them directly or not. As this air passes over building surfaces, where a surface area is cooler than surrounding materials, these particles are usually deposited at a higher rate (due to higher moisture on the cooler surface).

Readers should see HEAT LOSS in BUILDINGS. Also see AIR SEALING STRATEGIES and AIR LEAK DETECTION TOOLS as well as AIR LEAK MINIMIZATION. For photos of snow melt on rooftops that also show points of building heat transfer and loss, see STAIN DIAGNOSIS on BUILDING EXTERIORS.

Thermal tracking stains may appear on the building walls themselves, in a pattern of vertical "stripes" which may be roughly 16" or 24" on center, marking the (cooler) location of wall studs or ceiling joists.

In this case the exterior wall surface (see that window at right in the photo) are cooler where the wall studs are located and warmer between the wall studs. Probably the wall cavity is insulated, and the insulated areas have a higher "R" value than the solid wood studs themselves.

So the wall is cooler where the studs are located, increasing condensation on those surface areas, and picking up a greater share of house dust in air moving across those surfaces.

Thermal tracking stains may appear as dark black/brown wall stains appearing close to floor level, above heating baseboards mounted on exterior walls are probably due to thermal tracking.

Wall Stains over Heat Sources such as Hot Water Baseboards

Heaters can cause other dirt or soot stains on walls: But beware, a baseboard heater itself causes an air convection current up through the heating baseboards and in a dirty home or in a home occupied by pets or smokers similar stains may appear on other building interior walls (such as in this photograph) even if the wall is well insulated.

If staining appears vertical and at intervals thermal tracking is probably occurring.

The stain and soot deposition pattern over heaters is complicated by variations in the heat and air movement coming out of the heat source, and may not always accurately map wall stud or insulation locations.

More wall stains from heat sources such as over an air supply register in a floor are described at Other Stains on Indoor Walls & Ceilings and ceiling stains from heating or air conditioning registers are described at Stains HVAC Supply Registers.

Why Black Stains May Appear on Building Interior Walls as Well as on Building Exterior Walls

Our photo at below left shows wide black rectangular stains on a wall where insulation was omitted. The photo at below right shows long narrow black stains on a wall where thermal tracking marked the location of wall studs, but where insulation was present. Why did both of these patterns appear in the same building?

High interior moisture (air handlers in wet crawl spaces, a wet basement) was most likely the determining factor in the extent of staining that occurred in this home. Moisture condensed (and caused adhesion of house dust particles) on cooler surfaces. In some areas the un-insulated wall was coolest and got stained (below left) while in other areas the wall studs were cooler than the insulated wall cavity, so the stud-areas got stained (below right).

Black, roughly rectangular stains on building interior or exterior walls: may be present wherever insulation has been omitted. While usually these stains are going to appear on the building exterior walls (which get colder) they may appear on interior walls as well. These stains on interior walls, which may be completely un insulated, may appear with greater severity where other construction details increase the flow of air and/or moisture in certain sections of wall cavity.

An example of the cause of this stain pattern is air movement up through the wall cavity from a cool, damp basement or crawl space. The heated building living space warms the open interior wall cavity, causing air in that cavity to rise by natural convection towards the building attic or roof cavity.

Air movement upwards in the wall cavity draws cooler air from the basement or crawl space. Where some wall sections have more air movement, less insulation, or greater moisture exposure, they may become more darkly stained than their neighbors or more darkly stained than other walls in the building interior.

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.

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Thanks to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and content suggestions regarding thermal tracking.

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.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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ASHRAE resource on dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries. The following three ASHRAE Handbooks are also available at the InspectAPedia bookstore in the third page of our Insulate-Ventilate section:
- 2005 ASHRAE Handbook : Fundamentals : Inch-Pound Edition (2005 ASHRAE HANDBOOK : Fundamentals : I-P Edition) (Hardcover), Thomas H. Kuehn (Contributor), R. J. Couvillion (Contributor), John W. Coleman (Contributor), Narasipur Suryanarayana (Contributor), Zahid Ayub (Contributor), Robert Parsons (Author), ISBN-10: 1931862702 or ISBN-13: 978-1931862707
- 2004 ASHRAE Handbook : Heating, Ventilating, and Air-Conditioning: Systems and Equipment : Inch-Pound Edition (2004 ASHRAE Handbook : HVAC Systems and Equipment : I-P Edition) (Hardcover)
  by American Society of Heating, ISBN-10: 1931862478 or ISBN-13: 978-1931862479
  "2004 ASHRAE Handbook - HVAC Systems and Equipment The 2004 ASHRAE HandbookHVAC Systems and Equipment discusses various common systems and the equipment (components or assemblies) that comprise them, and describes features and differences. This information helps system designers and operators in selecting and using equipment. Major sections include Air-Conditioning and Heating Systems (chapters on system analysis and selection, air distribution, in-room terminal systems, centralized and decentralized systems, heat pumps, panel heating and cooling, cogeneration and engine-driven systems, heat recovery, steam and hydronic systems, district systems, small forced-air systems, infrared radiant heating, and water heating); Air-Handling Equipment (chapters on duct construction, air distribution, fans, coils, evaporative air-coolers, humidifiers, mechanical and desiccant dehumidification, air cleaners, industrial gas cleaning and air pollution control); Heating Equipment (chapters on automatic fuel-burning equipment, boilers, furnaces, in-space heaters, chimneys and flue vent systems, unit heaters, makeup air units, radiators, and solar equipment); General Components (chapters on compressors, condensers, cooling towers, liquid coolers, liquid-chilling systems, centrifugal pumps, motors and drives, pipes and fittings, valves, heat exchangers, and energy recovery equipment); and Unitary Equipment (chapters on air conditioners and heat pumps, room air conditioners and packaged terminal equipment, and a new chapter on mechanical dehumidifiers and heat pipes)."
- 1996 Ashrae Handbook Heating, Ventilating, and Air-Conditioning Systems and Equipment: Inch-Pound Edition (Hardcover), ISBN-10: 1883413346 or ISBN-13: 978-1883413347 ,
  "The 1996 HVAC Systems and Equipment Handbook is the result of ASHRAE's continuing effort to update, expand and reorganize the Handbook Series. Over a third of the book has been revised and augmented with new chapters on hydronic heating and cooling systems design; fans; unit ventilator; unit heaters; and makeup air units. Extensive changes have been added to chapters on panel heating and cooling; cogeneration systems and engine and turbine drives; applied heat pump and heat recovery systems; humidifiers; desiccant dehumidification and pressure drying equipment, air-heating coils; chimney, gas vent, fireplace systems; cooling towers; centrifugal pumps; and air-to-air energy recovery. Separate I-P and SI editions."
- Principles of Heating, Ventilating, And Air Conditioning: A textbook with Design Data Based on 2005 AShrae Handbook - Fundamentals (Hardcover), Harry J., Jr. Sauer (Author), Ronald H. Howell, ISBN-10: 1931862923 or ISBN-13: 978-1931862929
- 1993 ASHRAE Handbook Fundamentals (Hardcover), ISBN-10: 0910110964 or ISBN-13: 978-091011096
Dust from the World Trade Center collapse following the 9/11/01 attack: the lower floors of this building contained spray-on fire-proofing asbestos materials.
Energy Savers: Whole House Systems Approach to Energy Efficient Home Design [copy on file as /interiors/Whole_House_Energy_Efficiency_DOE.pdf ] - U.S. Department of Energy
"Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
"Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
"Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
"Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
"Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
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