InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
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.
Methods Used to Inspect the Chimney or Chimney Flue Interior
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
Masonry 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:
The chimney is constructed of a single-wythe brick thickness - and is a gas leak and fire hazard
The chimney is unlined
The chimney has thick creosote or soot inside
There are indications of broken, falling masonry or flue tile components
There is evidence of water leaks or frost damage inside the flue
The inspector might simply hear the noise from another appliance, perhaps on another floor, indicating a surprise shared-flue
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.
Reader Question: (Aug 12, 2012) John said:
I am getting a pale, sand colored, crystalline buidlup around the joints of my less than one year old I metal flue liner and the stuff has even dripped onto the top of the oil burner box which is also less than a year old. Looking through the flue damper, which is right next to the base of the chimney, I see only rust, which I am also not happy about. What is this stuff and how is it getting into my flue? Thanks
Reply: John, it sounds as if there is a condensation or leak problem in that chimney or the flue vent connector as well as deterioration. If the metal "flue" you describe is the actual chimney I'd ask a certified chimney sweep to inspect, clean, repair the system. Else it may be unsafe. If the metal flue you describe is actually the connector betweeen the heating appliance and the chimney, that's a job for your heating service technician.
(Oct 28, 2011) mark daniels said:
my 8"round chimney thimble is broken off flush with the concrete block and im trying to install a pellet burning stove how can i fix the thimble? cani add to the thimble?
(Nov 2, 2012) rodney calhoun said:
im replacing a mortat cap on a large hollow with only 2 clay flue liners should their be bore brick around liner
Ask a Question or Search InspectApedia
Questions & answers or comments about choices among procedures for inspecting the condition of chimney flues
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
The Home Reference Book, a reference & inspection report product for building owners & inspectors. Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a ten percent discount on any number of copies of the Home Reference Book purchased as a single order. Just enter HRBUS10 in the order payment page "Promo/Redemption" space. Note: InspectAPedia.com ® editor Daniel Friedman is a contributing author.
Home Inspection Report writing materials, including the Horizon Software System that 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.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors
Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003 - These guidelines address the inspection of chimneys and stacks. Each guideline assists owners in determining what level of inspection is appropriate to a particular chimney and provides common criteria so that all parties involved have a clear understanding of the scope of the inspection and the end product required. Each chimney or stack is a unique structure, subject to both aggressive operating and natural environments, and degradation over time. Such degradation may be managed via a prudent inspection program followed by maintenance work on any equipment or structure determined to be in need of attention. Sample inspection report specifications, sample field inspection data forms, and an example of a developed plan of a concrete chimney are included in the guidelines. This book provides a valuable guidance tool for chimney and stack inspections and also offers a set of references for these particular inspections.
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
"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/Chimney_Inspection_Repair.php. 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
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
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.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 extensive home inspection education and report writing material.
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.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates 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.
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.
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 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