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Chimney Creosote Questions & Answers:
Frequently-asked questions (and answers) about the nature of, cause, cure, prevention, chimney creosote from wood-burning and some other heating equipment.
This article series describes the formation of creosote in wood-burning heating appliances such as woodstoves and fireplaces and gives advice on reducing the fire risk. Creosote deposits accumulate in all types of chimneys - masonry, or metal, where wood burning appliances are vented.
Question: causes of oily liquid leaking out of wood heater
(June 30, 2015) A. Weido said:
Lately I noticed this nasty yellow liquid dripping down the chimney, all around it pretty much, and it's not a lot. Maybe a few ounces make it to the floor of the basement, and look really yellow.
The liquid coming down the chimney is almost gummy, it's like sap almost, and in a few spots some has dried into a gummy trail just like sap along the exposed outside of the chimney in the basement. What could this be?
[Click to enlarge any image] At left, sketch of a masonry chimney showing its components at a fireplace, courtesy of Carson Dunlop Associates, a Toronto home inspection and education company.
2017/02/15 Jon said:
I have a wood furnace. I loaded it up and titned it down before leaving the other night so it would slow burn through the night.
When i got back there was a black oily liquid everuwhere in the ground around it, on the back, dripping from the lower part of the dmoke exhause ventbright bu wjere you close and open the vent and some on theninside of the door.
Could this be from the kind of wood that was burned or something else... Also a different question, is it ok to leave the ash door open and close everything else (the smoke exhaust valve and the smoke bypass rod) really get it going and staying going if i sm around it and want itbto really stay warm?
Reply: probably creosote from burning wood at a low temperature - also watch for beehives
Sounds like dissolving creosote or chimney deposits. I've also seen such mess oozing out of chimneys after bees had made a honeycomb therein.
Oily liquid from a wood-burning appliance is, especially under the circumstances you describe, most-likely creosote that has condensed in the wood-furnace flue and then leaked out of the system onto the floor below.
When you run a wood heating appliance very slowly the flue is cooler and the condensation rate of creosote increases.
See if you can spot where the creosote liquid was leaking out onto the floor, as it might also be that your flue sections or chimney sections are installed upside down. Normally the female end of each section faces "up" so small amounts of condensate drain back into the heater rather than leaking out at the section joints.
Watch out: accumulation of creosote in a chimney can result in a very dangerous chimney fire if later a hot fire ignites the creosote in the flue. A certified chimney sweep can tell you the condition and safety of your chimney and flue.
Yes the type and condition of wood is a factor in creosote production; particularly, green wood that has more sap content produces more creosote.
Research on the production of creosote from burning wood:
Ramdahl, Thomas, Ingrid Alfheim, Ståle Rustad, and Torbjørn Olsen. "Chemical and biological characterization of emissions from small residential stoves burning wood and charcoal." Chemosphere 11, no. 6 (1982): 601-611.
Lee, Robert GM, Peter Coleman, Joanne L. Jones, Kevin C. Jones, and Rainer Lohmann. "Emission factors and importance of PCDD/Fs, PCBs, PCNs, PAHs and PM10 from the domestic burning of coal and wood in the UK." Environmental science & technology 39, no. 6 (2005): 1436-1447.
Excerpt from Baker whose article appears in a USFPL PDF
Unburned volatiles resulting from incomplete combustion of wood can cause a large loss in efficiency. These volatiles are also a source of trouble in stoves and furnaces because of the creosote, tarry substances, and acetic they contain.
To burn these volatiles, sufficient air must be supplied around or over the fuel bed. This air must be mixed with the volatiles while they are still hotter than l,lOO°F and
have not come in contact with cooling surfaces.
Theoretically, it takes six pounds of air to burn one pound of oven-dried wood, but actually more air is required because the air and
volatiles are not thoroughly mixed. (Baker 1982)
Question: chimney safety steps when changing fuels
(Nov 29, 2011) question said:
We have a hundred yearl old house. AT one time it used a wood burning stove in the kitchen.
The wood burning stove was replaced with a propane gas heater which was used for over 40 years. We have recently replace the heating system with a propane gas furnace, utilizing the same chimney.
The upper portion of the chimney had been replaced about 20 years ago.
Since we started using the furnace, we have a brown exudate which i assume is creosote leaking through the lower portion which had not been replaced.
What needs to be done to correct this? can it be corrected without replacing the whole chimney which runs from the basement through 2 stories and an attic?
Whenever you change the kind of fuel being used to burn and vent into a chimney, the chimney should be inspected for safety and if necessary cleaned. I suspect that your chimney was left with creosote deposits that should have been cleaned off. At this point, power cleaning might be needed.
If the chimney is otherwise sound and safe it can be used MAYBE: the flue that was suitable for venting a wood burning stove might not be the proper size for venting propane. Chimney size (and height and other factors) need to properly match the type of fuel and the BTU rate of the propane furnace.
You should have an expert check your chimney, but also take a look at FLUE SIZE SPECIFICATIONS ( on this page Continue reading provides an INDEX to RELATED ARTICLES that includes a live link - ).
Question: is creosote smell dangerous?
(Mar 25, 2014) Anonymous said:
I have a multi fuel stove. Just been in loft and noticed a strange smell,on further inspection ive noticed a tar like substance running down chimney breast could you tell me if this is serious.
Creosote leaking out of a flue is itself corrosive, and of course the leak out may mean air leaks in which can interfere with good draft; more serious would be enough creosote build up to block the flue (dangerous carbon monoxide gas poisoning) or to invite a chimney fire when you switch among fuels.
To be safe I'd have a professional inspect the flue and advise on cleaning needs as well as leak repairs.
Question: did snow cause a chimney fire?
(Sept 28, 2014) David Jones said:
Could snow build up on the outside cause a fire in the chimney if the log fire was just smoldering. Say it had been smoldering overnight and snow started at midnight could a fire in the chimney be started
Snow build-up would not be expected to *cause* a chimney fire but if snow build-up closed a chimney top a result might be smoke indoors as the chimney may no longer vent properly.
With some fuels there could be a more dangerous or even fatal carbon monoxide poisoning as well.
Question: fireplace makes chemical toxic odour - horrible to inhale it also stings the eyes
(Oct 2, 2016) Clare said:
I have moved into a rented old bungalow (about 100 years old at least). The previous tenant had taken the fireplace and the property had been unused and left in bad condition for 2 years.
The bungalow has been given an update including a fireplace surround created with a piece of wood for the mantlepiece and a woodburner installed. The fireplace surround is painted in what looks like black heat resistant paint.
The owner said the chimney had been cleaned about 9 months ago. The woodburner burns consistently without problem and gives off a good heat.
After about an hour there is a chemical toxic odour fills the room and all doors and windows have to be opened as it is not only horrible to inhale it also stings the eyes. So it would appear that the increase in the heat and length of time the fire has been burning is causing something to give this problem.
There is a large gap at the back of the wood mantlepiece that has been filled with fibreglass, the type you insulate lofts with. As it is open to the heat, could it be this? The carpets are new could it be that? Or could it be the creosote you talk about in you're excellent articles?
The masonry in the chimney will be old and i doubt that a liner was paid for to be put up there as things have been done on the cheap!
No smoke comes from the fire and once the heat dies down the smell does too. Any advice would be gladly taken. Hope you can help. Thanks Clare
Forgot to say that there is a regular sound when the fire is lit or unlit of falling bits down the chimney into the woodburner but not much evidence. - See more at: https://InspectAPedia.com/chimneys/Chimney_Creosote_Fire.php#sthash.mNr9c2gS.dpuf
Reply: stop using fireplace, ask for a safety inspection
Clare I cannot of course inspect by e-text, but what you describe sounds unsafe, including risk of a fatal building or chimney fire. I would not use the chimney nore wood stove until the system and chimney have been inspected by a certified chimney sweep or other qualified building official.
(Oct 11, 2016) Clare said: Hi, thanks for your reply. Awaiting the installer coming back from his hols! won't attempt to use till he has been.
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Questions & answers or comments about creosote: the rate of creosote deposition in chimneys, creosote and chimney fires, creosote odors & hazards, and how creosote is cleaned out of chimneys & flues.
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 "Creosote, what you need to know", UCLA Labor Occupational Safety & Health Program (LOSH), University of California, Los Angeles, Labor Occupational Safety and Health (LOSH)
Program, August 2003, web search 03/03/2012, original source: http://www.losh.ucla.edu/losh/resources-publications
/fact-sheets/creosote_english.pdf [copy on file as Creosote_UCLA.pdf].
 Preliminary Risk Assessment of Creosote, U.S. EPA, web search 03/03/2012, original source: epa.gov/pesticides/factsheets/chemicals/creosote_prelim_risk_assess.htm [copy on file as Creosote_Risks_EPA.pdf]
 Frequently Asked Questions [about creosote and chimney cleaning], Chimney Safety Institute of America, CSIA, CSIA Technology Center,
2155 Commercial Drive
Plainfield, IN 46168, Tel: (317) 837-5362, web search 03/03/2012, original source: csia.org/faqs/tabid/120/default.aspx
 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.
 National Chimney Sweeps Guild, NCSG, 2155 Commercial Drive, Plainfield, IN 46168, Tel: 317) 837-1500, Website: http://www.ncsg.org/ , Email: email@example.com
 National Fireplace Institute - NFI, Website: http://nficertified.org/ Quoting from the associations website:
The National Fireplace Institute® is the professional certification division of the Hearth, Patio & Barbecue Education Foundation (HPBEF), a 501(c)3 non-profit educational organization for the hearth industry.
 International Association of Fireplace and Chimney Inspectors, Inc., IAFCI, 5325 N Commerce Ave Ste 5 Moorpark, CA 93021, Website: http://www.membersiafci.org/
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
Ceramic Roofware, Hans Van Lemmen, Shire Library, 2008, ISBN-13: 978-0747805694 - Brick chimneys, chimney-pots and roof and ridge tiles have been a feature of the roofs of a wide range of buildings since the late Middle Ages. In the first instance this ceramic roofware was functional - to make the roof weatherproof and to provide an outlet for smoke - but it could also be very decorative.
The practical and ornamental aspects of ceramic roofware can still be seen throughout Britain, particularly on buildings of the Victorian and Edwardian periods. Not only do these often have ornate chimneys and roof tiles but they may also feature ornamental sculptures or highly decorative gable ends. This book charts the history of ceramic roofware from the Middle Ages to the present day, highlighting both practical and decorative applications, and giving information about manufacturers and on the styles and techniques of production and decoration.
Hans van Lemmen is an established author on the history of tiles and has lectured on the subject in Britain and elsewhere. He is founder member and presently publications editor of the British Tiles and Architectural Ceramics Society. Also available at the InspectAPedia Bookstore.
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.
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: firstname.lastname@example.org. 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