Barometric damper in chimney (C) Daniel Friedman A Catalog of Methods to Inspect the Interior of Chimneys & Flues

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Catalog of chimney interior flue inspection methods & techniques:

This article describes various methods that can be used to make a visual inspection of the interior of a chimney flue. Inspection methods taking advantage of existing openings such as at barometric dampers or chimney thimbles and cleanout doors can tell a lot about the condition of a chimney interior even though a complete view of the entire flue is not available.

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Methods Used to Inspect the Chimney or Chimney Flue Interior

Photograph of a damaged unsafe brick chimney in an attic.

Described in this article are more readily-accessible ways to inspect portions of the chimney flue interior by eye. Also see CHIMNEY FLUE INSPECTION CAMERA for a discussion of chimney inspection camera systems.

While none of these methods is comprehensive, valuable information can be easily obtained by putting two and two together combining visual clues about a chimney.

We recommend that you have any questionable chimney inspected by a professional and if necessary, make use of a remote camera and lighting to complete a detailed examination. But you can also make use of the methods we describe in this article.


First, Some Simple Indoor Clues Can Suggest Very Serious Chimney Hazards

Odors from a chimney or from heating equipment, high levels of indoor moisture, trouble keeping a gas burner going, rust on top of a heating appliance are examples of indoor observations that could indicate a very dangerous blocked chimney even before the homeowner or home inspector has approached the chimney itself.

Evidence of flue gas spillage may be easy to spot, especially with gas-fired equipment. For example, the rust on the top of this gas-fired heating boiler was from a long history of spillage from the boiler's draft hood.

The flue gases were spilling out of the draft hood because the chimney was blocked by fallen bricks which had jammed up in the flue right above the thimble for the boiler. The bricks had fallen from loose masonry up in the attic - as we showed by photos just above.

The homeowner contacted us to ask for a diagnosis of the high level of water found on basement walls, not because she suspected an unsafe chimney and indoor carbon monoxide hazards.

Chimney Flue View by Barometric Damper or Flue Vent Connector and Thimble

Barometric damper in chimney (C) Daniel FriedmanMasonry flue interiors:

It may be possible to obtain a limited view of the chimney interior by looking through the hinged door of a barometric damper, flue vent connector (disassembly required) or thimble (disassembly required), or where no flue vent connector is installed, if you find a cover closing off a previously-used chimney thimble, such as the old spring-loaded metal "pie plate" chimney thimble covers, it may be possible to inspect the chimney interior through those openings.

You may not be so lucky as to find a barometric damper giving view directly into the chimney flue (photo at left) but check to see if the draft regulator on a heater or water heater gives view into the chimney.

This damper location, built right into a chimney works properly only if just a single appliance is vented into this flue.


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, rust, holes, heavy creosote, leak evidence, and for metal flue blockage.

Metal chimney flue interiors & metal chimney liners have to be inspected from the chimney top and inside 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.

Even when a home inspector cannot see much of the chimney flue through such a limited access opening, certain observations can be critical, such as:

Chimney Thimble Requirements

A chimney thimble is a sleeve embedded in the chimney wall designed to accept the flue connector from an appliance. They must be placed with the chimney end flush with the inside wall of the flue lining and cemented in place with the refractory mortar used in the flue tiles.

Chimney Thimble Damage and Safety Concerns

The thimble is the masonry or clay or insulated metal sleeve that provides an entry passage for a metal flue vent connector to enter a masonry chimney.

The most common defect we see at the chimney thimble is failure to seal the metal flue at the entry to the chimney 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.

Readers of this article should be sure to review FIREPLACE DAMAGE & UNSAFE HEARTHS, and also see FIREPLACE INSPECTIONS for a professional chimney sweep's fireplace and chimney hazard checklist.

at FIREPLACE INSERTS we discuss fireplace inserts and zero-clearance fireplaces, both antique and modern, and their hazards and inspection limitations.

Readers should also see INACCESSIBLE CONNECTIONS FIREPLACE, WOODSTOVE. The inspection of chimney interiors is discussed at CHIMNEY INSPECTION, FLUE INTERIOR.

Chimney Inspection Guides


Continue reading at CHIMNEY FLUE INSPECTION CAMERA or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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