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Chimney Inspection Photo Guide - How to Perform a Visual Chimney Safety Inspection ChimAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com How to inspect chimneys How do we inspect a chimney for safety? This article provides detailed text and visual instructions for safety inspection of chimneys for safety and other defects such as a service which may be performed during a home inspection. An abbreviated version of this article first appeared in the ASHI Technical Journal, January, 1994; extensive edits, updates and additions have been made by DJ Friedman periodically through February 2007. This article is a chapter of our Also see the Chimneys Home Page © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

Inspecting chimneys from ground level

Curved masonry chimneys:

The condition of the top exterior section of the chimney and the exposed flue liner will generally reveal the soundness of the chimney above the roofline. The exterior of the upper portion of a chimneyt can be seen from the ground level though not in detail. The first photo here shows even from a distance that the chimney is curved, so we'd be alert for flue damage or for evidence that the chimney has separated from the building. Any movement in a masonry chimney risks damage to its interior liner and could be a safety concern. The second photo above shows a chimney to viewed from the ground, with our camera zoomed, and photographed during a rainstorm - not an unusual inspection condtion. We can see some incomplete repairs to a brick at the chimney top and other spalled, loose bricks. This chimney needs further inspection and probably some repairs, as well as a rain cap.

Chimney Movement detected outdoors:

Movement such as curving or leaning or separation from the building, especially in masonry chimneys, can cause damage to the flue liner or openings that might admit sparks (fire risk) or gases (carbon monoxide hazards) into the building structure or even into occupied spaces. The photographs here show a chimney which probably lacked a good footing, possibly aggravated in its lean by roof spillage onto the area where a footing should have heald the chimney steady. As the chimney leans away from the house we might find several problems: Damaged, unsafe chimney liner Damaged, unsafe fireplaces where the chimney has pulled the firebox away from the building or created dangerous openings around the fireplace into the building structure, risking both sparks (and fire) or air leaks (and inability to control the draft). Leaks into the building walls The usual repair is to remove and replace the chimney, though in some cases it may be possible to jack an intact masonry chimney back to level and repair its connections into the building.

Attempts to hide chimney movement

Attempts to hide chimney movement can be dangerous since if there is a safety problem the building owner or inspector may not pick up its clues. The fresh and thick band of caulk between the chimney and the wall as shown in this photograph were traced to a chimney separation that had been "repaired" simply by more caulking at the wall. Sometimes we see a chimney that has been "repaired" in this manner several times, with several generations of concrete or caulk or wood trim strips. Such chimneys should be inspected by an expert to assure that they're safe. If I see such a chimney that already has been re-lined I speculate that it may have been inspected and repaired but we'd still want to know just what was done. If the chimney moved further after the liner was installed, connections between vented appliances or a woodstove and the chimney flue liner could have opened and thus might be unsafe.

Damaged chimney top masonry:

Damaged chimney top masonry such as missing bricks and a missing chimney cap were easily spotted from ground level at both of the homes shown here. The home inspector or owner should ask, "Where did those bricks go? are they blocking the flue? Is the flue damaged and unsafe? What repairs are needed before we install a chimney rain cap?" This chimney may be too short as well - tough to call from ground level.

Cracked chimney masonry

Cracked chimney masonry such as shown in this photo of cracks in a brick chimney exterior, may a safety concern if the flue liner or chimney are not intact and fire/gas safe. Cracks such as shown here may be caused by improper original chimney construction. OPINION: if the mason does not leave an expansion gap surrounding the clay flue liners as they are set into the chimney during construction, as the flue heats up during use, the expanding flue may crack the surrounding brick. The second cracked chimney is a bit more suspect because we see what might be traces of soot or creosote having washed out through the cracks to the chimney exterior. If this proves to be the case this flue is certainly seriously damaged.

Inspecting chimneys from on the roof

An on-roof inspection of the chimney allows inspecting the upper portion of the flue lining, cap and roof flashing, chimey top seal or "crown", and it permits a closer inspection of masonry chimneys for cracking or other damage that might not be visible from a more remote "from ground" inspection.

Loose Wobbly Chimneys:

This chimney rocked and nearly fell over when we leaned on it a bit while climbing onto this roof. Pushing gently on a tall flue like this should not produce easy movement. But be careful! Don't try this at home and certainly not when there are people below, or when the flue is in use or probably any other time. A good wind could blow this chimney down. If the flue were intact and there was no other damage it might be possible to secure the chimney against movement. An expert was needed to decide how to make this one safe.

Chimney Flashing Mistakes

such as shown in these photos are remarkable for the number of errors, the leak history at this home, and the chances of related damage to the surrounding wood structure from insects or rotrot, or damage to the chimney itself from frost. The new roof was installed with a bare half-inch of vertical side flashing along the chimney and no counter flashing. The previous roof or chimney flashing was installed with no counter flashing, relying on roofing mastic to seal this juncture. Cracks and openings at chimney flashing admit wind-blown rain into the structure. An inspector with binocular vision might have found this crazy flashing installation from the ground. Maybe.

Chimney to Roof Clearance:

From the ground you can guess and from on-roof access you can measure to determine if a chimney is simply too short for fire safety and code compliance. The top of the flue should be at or above the height of a horizontal line draw from the chimney to the point at which that line touches the roof surface. Or the chimney should be at least two feet above the ridge. This photo is slightly incorrect (I didn't want to lose my tape down the flue while taking the picture). Measure from the edge of the chimney flue closest to the roof, horizontally, until you touch the roof surface to get this clearance distance.

Check the chimney top for damaged masonry (or rusted metal), a missing cap, damaged, craked, or missing top seal or crown on the top of a masonry flue, and here, an important discovery (at least in some jursidictions) is whether or not the chimney is single wythe or thicker masonry and whether or not the chimney has (or perhaps needs) a chimney liner.

Cracked chimney top seal:

Our photo at our "Introduction" and repeated here shows a chimney with a cracked, damaged, leaky top seal and missing rain cap on the flue. This chimney needs repairs to its top seal and also it needs a rain cap. Various experts have proposed design details to avoid cracking at the flue liner/concrete interface at the chimney top. Inspecting homes in both cold and hot climates, wherever we've seen chimney top damage of the sort shown here, it was traced to water (or frost) and not to the absence of a magic expansion gasket.

Unlined chimney flues

Unlined chimney flues might be safe if there is sufficient thickness of masonry and the flue is not damaged. Our photo shows an unlined chimney flue which, by luck of illumination from our flash camera (digital camera settings are discussed below), also showed us that a common flue was being used to vent two fireplaces - a fire safety code violation in some jurisdictions.

Re-lined chimney flues?

When a masonry flue has been damaged and is unsafe, a chimney sweep or repair company may propose chimney re-lining to improve the chimney's safety and performance. Actually from outside we're not sure what we're going to find at this property. Is this an attempt to "re-line" a bad chimney flue or was it an attempt to vent some other heating appliance up and out through an existing chimney? Is the chimney in use by two different heating systems or just one? A professional chimney re-lining operation would have not left a chimney like the one shown here using easily rusted steel, no protection from weather or animals at the top, flimsy mounting of the metal flue, possibly an under-sized flue, possibly an unsafe sharing of a chimney between two different heating systems or sources. The owner or inspector should be very nervous about this installation and should investigate it further.

Obstructed or Blocked Chimney Flues

Obstructed or Blocked Chimney Flues might be discovered by inspection and luck as shown here. A hornets nest is partly blocking this flue. Not only may there be a chimney safety or performance problem, there could be a problem for the inspector or the building occupants when the hornets are distrubed. A meticulous chimney mason would also criticize the mason who built this chimney for leaving oozed mortar sticking into the flue between each pair of flue tile liners. That detail can make a chimney hard to clean and can make for damage and flue leaks if the mortar "ears" are broken off during chimney cleaning. We were able to take this clever photo of a dark chimney interior by using our maglite (TM) flashlight along with a Nikon Coolpix 4500(TM) camera on which we re-set the ISO or equivalent film speed to its highest setting (800). This trick with a digital camera will sometimes let an inspector "see" into a pretty dark area.

Inspecting chimneys from inside a building

Interior basement and attic inspections will reveal corrosion at the cleanout door, connector problems and flashing leaks.

Inspect exterior of chimneys:

Inspect the exterior of the while you are inside the building. Attic access to a chimney or basement access, may provide key inspection points since there the chimney is likely to be directly accessible and there may be cleanout or other access ports to check the condition of the chimney interior. In this photo the exterior of this chimney, visible in an attic, was in very poor condition, with soft spalling bricks. Worse, there was an immediate fire and gas hazard since there were actual openings at the base of this chimney where it passes through the attic floor framing. This is a serious fire hazard and a flue gas leak hazard. This flue is unsafe. Inspect the entire route of the chimney through all building areas. Even if the chimney is not directly visibile you may find evidence of leaks, movement, or old chimney penetrations, say for a woodstove, that may not have been safely closed.

Missing chimney bricks:

this photo shows a homeowner "repair" involving putting aluminum sheet metal over a hole in their chimney to make it "safe" - removing the metal disclosed a nice hole where bricks were missing. We asked the homeowner where s/he thought those bricks had gone? This was an unsafe chimney. The second photo shows the chimney hole with the sheet metal removed. The bricks had fallen down and blocked this flue, creating a carbon monoxide hazard.

Chimney Movement detected indoors

Chimney movement in masonry chimneys can cause damage to the flue liner or openings that might admit sparks (fire risk) or gases (carbon monoxide hazards) into the building structure or even into occupied spaces. The photograph here shows a leaning, corbelled brick chimney in a pre-1900 home. When inspecting an old chimney which was corbelled over at an angle to come out at the center of the building roof's ridge (done for aesthetic reasons) inspect the chimney carefully at the attic floor where the chimney changes from angled (corbelled) to vertical. If the corbelled flue has sagged along with the roof, the chimney may be cracked and open at this point even though other cracks were not seen.

Abandoned chimneys

in an attic can be a big surprise. We often wonder what's holding up all this weight. Someone may have eliminated a fireplace or an entire chimney on the lower floors, but neglected to remove the chimney from the attic out through the roof, perhaps because they didn't want to repair the ensuing hole in the roof left if the chimney were removed. Point loads from unanticipated weight or even a sudden collapse can be a real hazard if chimney bricks suddenly come through an upper floor bedroom ceiling.

Inspect the chimney interior

Missing or open chimney cleanout doors:

In this photo the chimney cleanout is easy to find but isn't that door missing? No not in the first photo at left of this pair of photographs of chimney cleanout doors. But look carefully at the second photo. Even though a cleanout door is installed, masonry has fallen out above the door, giving an opening right into the flue. A missing chimney cleanout door or any other hole in the flue means that there is a fire safety hazard (sparks or ashes falling out onto the basement floor) and also that it is impossible to control the draft in the flue. Where the hole in a chimney is lower than or below the flue vent connector joining the heating appliance to the flue, there is also a serious problem with draft control. I've found heating boilers with draft problems and "repair attempts" like removing the boiler's barometric damper, when all the while the root problem of bad chimney draft was that the cleanout door was open or missing. Where you can find a chimney cleanout or can remove a flue vent connector to look into a flue, use of a mirror inside the flue to fiew the flue from below. This is by no means a thorough and accurate view of all of the chimney flue interior. But if the chimney was constructed as a straight flue up through the building roof, you should see daylight - otherwise the flue has become blocked, perhaps with nesting animals or collapsing debris.

Metal chimney flue liners have to be inspected by removing the vent connector from the chimney breach to check for corrosion. Sight up the liner with a mirror to check straightness and for blockage.

Inspecting chimney flue interiors using remote cameras and lighting

Peering up into a chimney flue from below or down into a flue from a rooftop access point, even with a bright light, is pretty much staring into a black abyss. It is difficult to see all of the interior chimney surfaces. Quite a few chimney cleaning companies offer a camera service which is in essence, a fisheye lens attached to a video camera which is lowered through the flue.

A "Chimscan (TM)" is a common chimney inspection system you may hear about. Chimney inspection cameras permit a more careful inspection of the condition of the entire flue interior.

Especially on older masonry flues of unknown condition, this step can be quite valuable in assessing the safety and security of the flue against fire, spark, or gas leaks.

Chimney Inspection Tips and Tricks

A good field investigator uses all available information in assessing the condition of building components, not just the obvious. Here are a few indirect observations that might be important clues about hidden chimney safety defects at a property:

• Dead-end flues, chimneys whose flue stops right at the point of entry of a thimble for a woodstove or heating appliance are inherently more dangerous than a conventional flue which extends several feet further past the thimble. Dead end flues are quickly and easily blocked by any debris that might fall down a chimney. If a chimneys venting a gas-fired appliance becomes partly or totally blocked, the applicance is likely to rapidly produce very dangerous, potentially fatal carbon monoxide (CO). Be sure that chimneys of this type are inspected and cleaned annually and be sure that you have working CO detectors as well as smoke detectors in the building.
• Masonry fragments: if you open a chimney cleanout-door or pull the flue vent connector from a dead end chimney flue, in either case you are looking at the very bottom of the chimney flue. If you are inspecting a masonry chimney, be alert for discovery of masonry fragments when inspecting or cleaning the bottom of the flue. If a piece of brick, masonry block, concrete, or clay flue tile liner is pulled out of your chimney, ask "where do you suppose this came from?" If the masonry scrap fell during construction of the chimney it may mean nothing. But if it fell because the chimney has been damaged, perhaps by water, frost, or during cleaning, then you probably have an unsafe chimney flue - more investigation is in order, promptly. Certainly if you believe that the masonry scrap found at the bottom of a flue fell during original construction, and if you remove it during cleaning, you should never find another piece in the flue bottom. If you do, the flue has been damaged anew and it is unsafe.
• Chimney leak history: leak stains inside the building attic or on any floor, if they are traceable to leaks at a chimney, are reason to be concerned for possible water damage to the chimney as well as to the building. Further investigation may be warranted.
• Chimney cap history: if a chimney has spent part of its life with no cap installed, there is extra risk of water damage to the flue interior. In a masonry chimmey damage may appear as frost cracking of the upper flue liners or masonry. In any chimney, there may also be water damage to the heating appliances being vented by that chimney.

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More Problems with Chimneys - Moisture Damage to Chimneys

Moisture is the major cause of chimney corrosion and disintegration in both masonry and metal chimneys. The flue gases are acidic in nature and if allowed to condense and saturate the masonry or joints in metal flues the destructive results will soon be apparent. Mechanical problems in the construction or settlement after construction and overfiring or flue fires will also contribute to the problems.

External moisture enters the chimney through cracked caps, porous masonry, poor mortar joints and improperly designed and installed roof flashings. Internal moisture (condensation) collects in cracked or separated flue tiles, blocked flues and chimney caps.

Masonry chimneys subjected to moisture damage can have efflorescent salt stains, spalled bricks, eroded mortar joints, flaked cracks in the ceramic flue liner and cracked caps.

Metal components of a vent system can have rust and white acid stains at joints, corrosion holes along the bottom of horizontal connectors and corroded chimney cleanout doors at the base of the flue.

A broken or short thimble can allow combustion gases to rise in the air space between the flue liner and the masonry surround. Condensation stains will often appear in the mortar joints and as streaks running down the exterior face of the chimney. Wood or oil burners leave soot that leaches out as black streaks.

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Technical Reviewers

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• Daniel Friedman - principal author
• Technical reviewers are invited to comment or ask questions - contact us

More Information on Chimney Safety, Chimney Inspection, Chimney Testing, & Building Inspections

• Chimneys, flues, wood stoves & fireplaces: chimney inspection, defects, safety concerns
• U.S. vs. Canadian Unlined Masonry Chimney Flue Requirements & Case Study
• Metal Chimney Safety Alert - CPSC Document #5047.
• Chimney Safety Alert for Wood Burning Appliances - US CPSC Alert Document 5017, wood stoves, fireplace inserts
• "Chimneys and Flues materials, safety standards, requirements," D. Cohen, ASHI Technical Journal, with edits, updates, and additional text by Daniel Friedman.
• NFPA 211 - 3-1.10 - Relining
• NFPA 211 - 3-2 - Construction of Masonry Chimneys
• NFPA 211 - 3-3 - Termination Height
• NFPA 211 - 3-4 - Clearance from Combustible Material
• NFPA 54 - 7-1 - Venting of Equipment
• 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, April, 1992
• Chimney Safety Institute of America - Chimney Fires: Causes, Effects, Evaluation
• National Chimney Sweep Guild - Yellow Pages of Suppliers
• SaverSystems, Div. of Meredith - Water Repellent Technologies

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