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Chimney Stains, Discoloration, Leak, Diagnosis, Cleaning & Repair Guide
How to diagnose & clean or cure stains on chimney exteriors or on building exteriors caused by chimney defects
- CHIMNEY STAINS & LEAKS - How to diagnose, evaluate & cure stains on masonry & metal chimneys & on roof or other building surfaces near or below chimneys
- What do dark oozing stains mean on a metal or masonry chimney exterior indoors or outside?
- What do white powdery stains mean when found on a masonry chimney exterior indoors or outside?
- How to Evaluate & Diagnose Black or Brown Stains on Chimney Exteriors
- Water and Chimney Leaks Lead to Damage that may show up indoors on walls
- Indoor Stains & Wall Damage May Be Traced to Chimney Leaks
- Fireplace Stains May Indicate Chimney Leaks & Damage
- Stains and leak damage to a chimney may be visible in the attic
- Stains, cracks, evidence of chimney leaks & damage may be visible in the basement
- CHIMNEY STAINS, INDOORS - separate article
- EFFLORESCENCE, Salts & White / Brown Deposits - separate article
- RUST STAINS on ROOFS - separate article
- STAIN DIAGNOSIS on BUILDING EXTERIORS - separate article
- Questions & Answers about the cause, significance, and cure of stains on chimneys both outside and within buildings
- References
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
How to diagnose & evaluate stains on chimneys outdoors or indoors & where to look for signs of chimney damage. This article describes stains that appear on chimney surfaces both indoors and outside. We identify common dark brown or black stains as well as white or light-colored stains or white powdery material that appears on masonry chimney surfaces. We explain what these chimney stains might mean, why safety hazards may be present, and how to proceed to inspect and repair the chimney.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Significance of Stains on a Chimney Exterior Surface: Creosote, soot, water
Here we discuss stains found on or at chimneys themselves both on the building exterior, and in the building interior at walls or ceilings near chimneys. Also see Chimney-Caused Roof Stains where we discuss staining on roof surfaces traced to problems at chimneys.
Diagnosing White Efflorescence Stains on Chimney Exteriors
White powdery or crystalline stains on masonry chimneys is often efflorescence, a mineral salt left on the surface as water evaporates. Efflorescence may appear on the outside surfaces of a chimney both outdoors and inside as well as inside the flue itself.
(You are not likely to see these stains on a metal chimney unless the metal chimney and flue are damaged and leaking insulation material.)
If you are not sure what efflorescence is or how to recognize it, see EFFLORESCENCE, Salts & White / Brown Deposits. Other examples of efflorescence on building foundation walls is in our discussion of white stuff that is not mold.
Efflorescence might be just cosmetic - as wind-blown rain wets the chimney sides and leaches out mineral salts which remain white on the masonry surface of the chimney.
But efflorescence might also mean that water is running inside of the chimney flue or chimney structure. Further diagnostic inspection is needed.
Left unattended, water entering a masonry chimney risks damage to the flue (unsafe) and to the chimney structure (unsound and unsafe).
At SLATE ROOF DEFECTS Questions & Answers we provide additional discussion about sources of white stains that may be found on chimneys or on roofs below or near chimneys. |
How to Evaluate & Diagnose Black or Brown Stains on Chimney Exteriors
This chimney is suffering water damage from at least two locations. The white efflorescence along the upper side of the chimney (at left) may originate at a bad chimney cap or rain cap.
But the chimney also seems to be suffering from roof runoff/spillage, perhaps due to a clogged roof gutter - as you can infer from the additional brown and black stains on the right side of this chimney from below the roof eaves.
Inside the building it is important to inspect building walls for signs of chimney leakage and it may be appropriate to have a professional inspect the safety and condition of the entire chimney flue.
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Notice the black stains originating at the chimney shoulder on its left side, and the cracking stucco on the chimney's right side in this photograph. If your chimney inspection began at ground level, both of these clues should raise a red flag and call for close attention to the chimney condition from both outdoors and inside the building.
This poor chimney, discussed in more detail at Chimney Movement, Ongoing vs Static, was leaning well away from the building - not so easy to notice when inspecting the chimney base shown at left.
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In our chimney photo at below left, notice the black and brown stains (and that odd rain cap) at the upper section of this masonry block chimney. Now without looking more closely we're not sure if we are seeing a history of creosote wash-down the chimney sides from a woodstove or other heater (the flue is too small for a fireplace), or alternatively, we might discover that the chimney interior flue is damaged, cracked, leaky, sending rain-washed creosote or condensate out thorough the chimney at cracks and mortar joints. This chimney needs expert inspection for safety and condition.
Oil Burner Soot Stains at & Below a Chimney
 At above right the black stains on the sides of this chimney near its top are probably soot or creosote wash-down.
The chimney flue is short, the chimney cap is thin and cracked, and of course there is no rain cap (see CHIMNEY CAP & CROWN) . Look closely for frost damage at both the exterior and interior of this chimney. Photos of soot at a metal chimney cap and on the roof below were provided courtesy of ASHI inspector Roger Hankey.
Soot at the chimney top (photo at left & below left) , particularly on an oil or gas fired heating equipment flue, is a good indicator of improper equipment adjustment or a related chimney and draft operating problem.
Watch out: sooting gas fired heating equipment is very dangerous and risks production of fatal carbon monoxide gases in the building.
Our second example of a roof stain traced to a chimney is shown in our photo at below right - rusting metal chimney components. See ROOF STAINS from CHIMNEYS for details and for more examples of both of these chimney related stain topics.
Dark Algae Stains on Masonry Chimneys
The dark stains at the upper center of this brick masonry chimney are probably algae growing in higher concentration on the masonry surface that is most-wetted by runoff from the chimney top.
But we'd want to make an on-roof inspection from much closer to be sure we're not looking at soot deposition. |
SOOT STAINING - Black Soot Stains on Roof Shingles Around Chimneys
Roof stains due to chimney defects: this section on roof stains at or around chimneys describes how to identify and diagnosis of black roof stains caused by soot or creosote washing off of building chimneys and we discuss possible safety and fire hazards associated with this condition. Our chimney articles discuss all aspects of chimney inspection & troubleshooting, while our building stain diagnosis articles articles tell readers how to identify & explain the most-common causes of black, brown, red, gray, green,
or white stains appearing on roof shingles and on other building surfaces. This article focuses on stains on roofs caused by chimney problems.
Soot from fireplace flues washing down onto the roof - characterized by staining appearing below
and in line with the chimney
Similarly, soot from oil-fired heating flues washing down onto the roof,
characterized by the same pattern of staining around and below the chimney; also probably an indicator
of an operating problem with the heating system.
That was clearly the case in the photograph shown at page top.
At left our photo shows soot stains running down a masonry chimney and onto the roof surface. Incidentally, this chimney needed to be re-lined but evidence of that is not presented in this photo.
Gas Flue Safety Warning: If this same sooting appears on and around a gas-fired appliance
flue, there is a very unsafe condition present and risk of fatal carbon monoxide production inside
the building. Immediate action is be needed.
[Photograph of a soot-stained roof top at page top was courtesy of Roger
Hankey a Minnesota home inspector.
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The Location of Roof Stains Can Help Diagnose Their Cause
 Unlike other roof shingle stain patterns shown in our article series on roof stain diagnosis, black stains caused by soot staining from a chimney
or brown stains from a rusting chimney or chimney flashing, or sometimes a combination of the two will be prominent in a wide swath along the sides and below the chimney and will be little in evidence elsewhere on the roof.
Our photo of red-brown roof stains below and around a metal-enclosed chimney (left) was taken in Wappingers Falls, NY. The stains on this roof are around and below a metal enclosure that in turn surrounds a metal chimney.
A closer look at the chimney top shows black sooting - the heating system in this home has not been operating properly, and we pose that the roof and chimney stains are probably a combination of rust and soot wash-down from the sooty flue gases as well.
Watch out: we often see that the top of metal box frames around older metal chimneys has rusted through, but may not be noticeable from the ground. Sending water down the chimney risks costly damage to the heating furnace or boiler. Look for water leak stains on the flue and chimney base inside the building and inspect the chimney top carefully from outside.
Rust and red stains on roofs and chimneys are discussed in detail at RUST STAINS on ROOFS .
See Causes of Roof Stains and Catalog of All Roof Stains for the causes and types of stains that occur on building roofs. There are other sources of roof staining, from cosmetic to harmful to the roof.
For the diagnosis and cure of other building stains, see STAIN DIAGNOSIS on BUILDING EXTERIORS and STAIN DIAGNOSIS on BUILDING INTERIORS.
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Frequently Asked Questions (FAQs) about stains on building chimney exteriors
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- [1] Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - rhankey@hankeyandbrown.com. Mr. Hankey is a frequent contributor to InspectAPedia.com.
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
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.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
- Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - rhankey@hankeyandbrown.com. Mr. Hankey is a frequent contributor to InspectAPedia.com.
- NFPA 211 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
- NFPA #211-3.1 1988 -
Specific to chimneys, fireplaces, vents and solid fuel burning appliances.
- NFPA # 54-7.1 1992 -
Specific to venting of equipment with fan-assisted combustion systems.
- GAMA -
Gas Appliance Manufacturers' Association has prepared venting tables for
Category I draft hood equipped central furnaces as well as fan-assisted
combustion system central furnaces.
- National Fuel Gas Code, an American National Standard, 4th ed. 1988 (newer edition is available) Secretariats, American Gas Association (AGA), 1515 Wilson Blvd., Arlington VA22209, and National Fire Protection Association (NFPA), Batterymarch Park, Quincy MA 02269. ANSI Z223.1-1988 - NFPA 54-1988. WARNING: be sure to check clearances and other safety guidelines in the latest edition of these standards.
- Fire Inspector Guidebook, A Correlation of Fire Safety Requirements Contained in the 1987 BOCA National Codes, (newer edition available), Building Officials and Code Administrators International, Inc. (BOCA), Country Club HIlls, IL 60478 312-799-2300 4th ed. Note: this document is reissued every four years. Be sure to obtain the latest edition.
- Uniform Mechanical Code - UMC 1991, Sec 913 (a.) Masonry Chimneys,
refers to Chapters 23, 29, and 37 of the Building Code.
- New York 1984 Uniform Fire
Prevention and Building Code, Article 10, Heating, Ventilating, and Air Conditioning Requirements
- New York 1979 Uniform Fire Prevention & Building Code, The "requirement" for 8" of solid masonry OR for use of a
flue liner was listed in the One and Two Family Dwelling Code for New
York, in 1979, in Chapter 9, Chimneys and Fireplaces, New York 1979
Building and Fire Prevention Code:
- "Top Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
- Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
- "Rooftop View Turns to Darkness," Martine Costello, Josh Kovner, New Haven Register, 12 May 1992 p. 11: Catherine Murphy was sunning on a building roof when a chimney collapsed; she fell into and was trapped inside the chimney until rescued by emergency workers.
- "Chimneys and Vents," Mark J. Reinmiller, P.E., ASHI Technical Journal, Vol. 1 No. 2 July 1991 p. 34-38.
- "Chimney Inspection Procedures & Codes," Donald V. Cohen was to be published in the first volume of the 1994 ASHI Technical Journal by D. Friedman, then editor/publisher of that publication. The production of the ASHI Technical Journal and future editions was cancelled by ASHI President Patrick Porzio. Some of the content of Mr. Cohen's original submission has been included in this more complete chimney inspection article: InspectAPedia.com/chimneys/chimneys.htm. Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
- Natural Gas Weekly Update: http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp Official Energy Statistics from the U.S. Government
- US Energy Administration: Electrical Energy Costs http://www.eia.doe.gov/fuelelectric.html
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 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.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
- Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
- Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003
- NFPA 211 - 3-2 - Construction of Masonry Chimneys
- NFPA 211 - 3-3 - Termination Height for chimneys
- NFPA 211 - 3-4 - Clearance from Combustible Material
- NFPA 54 - 7-1 - Venting of Equipment into chimneys
- Brick Institute of America - Flashing Chimneys
Brick Institute of America - Proper Chimney Crowns
Brick Institute of America - Moisture Resistance of Brick
- American Gas Association - New Vent Sizing Tables
- Chimney Safety Institute of America - Chimney Fires: Causes, Effects, Evaluation
- National Chimney Sweep Guild - Yellow Pages of Suppliers
- ...
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