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CHIMNEY INSPECTION DIAGNOSIS REPAIR
BACKDRAFTING HEATING EQUIPMENT
CARBON MONOXIDE - CO
CHIMNEY COMPONENT DEFINITIONS
CHIMNEY FIRE ACTION / PREVENTION
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
FLAME COLOR, BLUE vs YELLOW COMBUSTION
HOME HEATING SAFETY
Moisture / Frost Damaged Chimney
ODORS & SMELLS DIAGNOSIS & CURE
Safety Recalls, Chimneys, Vents, Heaters
STAIN DIAGNOSIS on BUILDING EXTERIORS
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY
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.
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
How to Evaluate & Diagnose Black or Brown Stains on Chimney Exteriors
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
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.
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.
Frequently Asked Questions (FAQs) about stains on building chimney exteriors
Questions & answers or comments about the cause, significance, and cure of stains on chimneys both outside and within buildings
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.