These questions & answers about B-vent chimneys & vents were posted originally at the topic home page: TYPE B-VENT CHIMNEYS.
On 2017-02-15 by (mod) - chimney cap blew off of B-vent: ok to run the heater?
I'm a bit scared to bet your life and safety on a "yes" for a home and system about which I know not a darn thing, but in concept, the heat will work; the risk is downdrafts or inadequate draft - that could produce fatal CO - carbon monoxide.
If you're running the system while waiting for replacement of the missing cap be SURE you have working carbon monoxide detectors properly located, installed, tested.
On 2017-02-13 by C Stuart
We had a windstorm today and the vent along with its oval tpye B gas vent cap blew off the roof. Is it OK to turn on heat until it's repaired?
On 2016-10-28 by (mod) what to do about a hole in the inner metal pipe of a multi-wall metal chimney
For safety, and considering the risk of a fatal carbon monoxide poisoning or a fire at a building of which we know so little, if it were my job I'd replace the damaged section of B-vent.
If nothing else we're unsure how much remaining life there is in the inner pipe that you found as "undamaged"
On 2016-10-27 by Larry
my B. chimney has a 1 inch hole in the outer pipe, the inner pipe is undamaged. Is it safe to patch the outer pipe, then use metal tape to seal it? I await your advise thank you
On 2016-09-29 by (mod) trying to replace parts of the b type vent pipe from the attic thru the roof
I think the manufactuer question was asked because newer replacement sections of B-vent may not clip properly, nor safely, to older B-vent parts from a different manufacturer.
To replace parts and keep parts of the existing system, why not bring along a section of the existing B-vent when you're shopping? That way you can compare features and connections.
On 2016-09-28 by MIKE
My house was built in 1962 and I am now trying to replace parts of the b type vent pipe from the attic thru the roof. when I went to buy the materials they asked what manufacturer?
They told me it was stamped on the pipe? I can't find any stamping on any of the sections?
How do I replace this vent pipe?
On 2016-02-13 by (mod) For flat and very low slope roofs the above-roof chimney height may in some cases be less than two feet
Keep in mind that on these low slope or flat roofs, at least in some buildings, you'll need to consider the adequacy of draft - a too-short chimney may not provide enough draft, so its above-roof height may need to be extended for that reason.
I've clarified the text in the article. Thank you for careful reading and for taking the time to comment.
On 2016-02-13 by AaronBrauer
I'm confused. The article TYPE B-VENT CHIMNEYS states,"type-b vents should be at least two feet above the roof's surface."
But the table shows that they can be as short as one foot above the roof's surface. Huh?
(Oct 14, 2011) Chris said:
what is the definition of vertical wall regarding b-vent termination? Interior wall or exterior wall continuing higher than the roof
Chris, as we are terminating the B-vent outdoors and above the roof line, the "vertical wall" pertains to outside conditions.
(Oct 26, 2011) anthony pace said:
I have a Carrier mod. 58pav090-16 (Dec.1999)-the bottom of the flue pipe (cap) is corroded and has accumulated (sand like) debris. The pipe up thru the attic looks good and there is a raincap on the top.
When a gas flue vent or chimney is corroded it is potentially unsafe as it may perforate and leak. It most likely needs replacement.
Further, corrosion of a metal flue on gas-fired equipment is a red flag warning to look out for improper and thus unsafe heating appliance operation.
For example, insufficient combustion air, leaks into the chimney, improper chimney installation (too cold to vent properly) can increase the rate of flue corrosion while at the same time those conditions can threaten the production of dangerous, even potentially fatal carbon monoxide gas.
To be able to sleep safely while waiting for your chimney or HVAC expert, be sure you have working carbon monoxide detectors properly installed.
Question: elbows in vents
(Mar 22, 2012) Gettinitright said:
Is there any code regulation against installing 90's (elbows) 1 or 2ft from the protrusion of the roof? Updating a unit from 1990 and the new code says I need to have 1" clearance around all wood framing. I would like to install 2 elbows instead of cutting a new hole in the roof to effectively relocate it.
(Oct 30, 2012) Tom Painter said:
I have a two store house built in 1923. I was thinking of closing up the fireplace and walling it off. A new water heater and gas furnace vent a flue in the basement that by-passes the first floor fireplace. The top of the chimney leans a little and needs to be repaired. With the fireplace walled off, and its very existence hidden behind drywall, can I have the top rows of chimney bricks removed down to B vent height requirements?
(Nov 30, 2014) George Drexel said:
How far can I run b-vent horizontally from a furnace before turning upward?
George I can't guess at an answer on horizontal B-vent limits - as I think it depends on the appliance being vented. Smaller BTUs, for example will probably permit only shorter runs. An easy solution is to check the installation instructions for the appliance being vented - or tell us the appliance brand and model and we can help research the question.
(Apr 27, 2015) George said:
I have a B vent extending up thru the roof of a commercial building. We added a parapet wall 12" away from the vent.
It presently extends up 24" Do in need to extend up above the new parapet wall ?
I neglected to say the new parapet wall is 48"
George I think we've answered this in the clearances above and in a separate article that should be helpful:
B-Vents should be at least two feet above the roof surface as well. See the detailed table below and also see TYPE B-VENT CHIMNEY CLEARANCES - separate article compares with other chimney types.
If a vent terminates next to a wall it may fail both fire clearance and suffer draft interference. Your local building code inspector is the final authority so that's whom to ask. If I were inspecting (and I"m not) I'd want the vent to terminate 2 feet above roof components including a nearby parapet wall.
Question: code on passing a B- Vent chimney through a "sheetrock" wall
(July 23, 2015) woody email@example.com said:
what is the calif.code requirement for furnace (type B-vent) passing thru a sheetrock wall or can i use single wall
Please see the B-Vent clearance distances from combustibles given at inspectapedia.com/chimneys/Metal_Chimney_Clearances.php
There you'll see that for gas appliances you'd need 6-inches from combustibles (including drywall and wood framing)
Do not run a single wall flue vent connector to pass through building walls. You'd need (varying by location and local codes), typically 18" to combustibles.
Question: a rafter is in the way of the direct route for my B-vent chimney
(Aug 13, 2015) Robert said:
My gas furnace uses a B-Vent, I have a rafter in the way. Does the B-Vent have to be straight or can I use 2 90 degree with a short straight piece to go around rafter?
Robert, depending on total flue length and the free space available you may be able to turn around the rafter, but you may want to use 45's rather than 90's for better draft. I'd sketch the whole flue length and dimensions and then check once more with the appliance manufacturer to be sure they agree that it will vent adequately. A mistake could be fatal.
Question: why do B-vents rust near the chimney top and at the rain cap?
(Aug 30, 2015) gregh said:
Many experts seem confused as to why some b vent pipes tend to rust near the top under the rain cap. The rust has absolutely nothing to do with the age or condition of the gas appliance. The rust is a result of the flue gas coming in contact with the outer shell of the b vent which is a type of galvanized metal.
This outer shell is generally cool to the touch , so when the warm flue gasses contact the outer shell and condense on it over a long period of time rust will result as the flue gasses are highly corrosive. Several manufactures became aware of this 40 years ago. Selkirk designed a rain cap around 1971 which incorporated a lower ring shield to direct flue gas away from the b vent pipe. Both Selkirk and Ecco manufacturing sold a painted termination pipe from 1973-1985 .
By this time most cap designs used some type of shield to keep flue gas from drifting down onto the b vents outer surface. Also mid efficient furnaces are terrible for creating more corrosive vapor in flue gas as these appliances don't have a draft hood to introduce dilution air which would help dry the flue gas somewhat.
Interesting details, Greg, thank you. Indeed condensate from gas fired appliances is quite corrosive. Understanding just where the corrosion shows up is both diagnostic and interesting. We'll edit your comments into the article on Chimney wet time over at
(Oct 17, 2015) Ralph rangel said:
There is a machine screw sticking into the inner B-vent wall (flue.
it sticks in approx. 1/3".
Is this permitted by code (Chicago)
On 2015-12-30 at RID:11 by jim H. [delete]
wanted to find out, what are the requirements for installing a chimney in a half round building. i have a building im going to use as a shop to tinker in, and need some heat. any ideas. its getting cold and winter is coming.
Ralph: I don't know but I doubt that it's an issue (except on dryer ducting).
Jim you'll want to meet the same roof clearances and fire clearances as for other buildings, keeping in mind that I can't answer a question like this: we don't know the fuel, type of heater or what the heck you're venting.
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Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: firstname.lastname@example.org
Thanks to Luke Barnes for suggesting that we add text regarding the hazards of shared chimney flues. USMA - Sept. 2008.
Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at email@example.com
Roger Hankeyis principal of Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
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.
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.
"Chimneys and Vents", 789 CMR 68.00 Massachusetts Building Code, web search 10/15/2010, original source:
780 CMR: STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
THE MASSACHUSETTS STATE BUILDING CODE - quoting: 6801.11 Multiple-Appliance Venting Systems.
Two or more listed and labeled fossil fuel-fired
appliances shall not be connected to a common
natural draft venting system unless permitted per
applicable requirements of 248 CMR or 527 CMR.
For solid fuel-burning appliances, see 780 CMR
Chimneys and Vents, Chapter 18, M1801,model building code - [on file as Code_Chim_Res_C_18.pdf] - widely used by U.S. & Canadian Municipalities,
"Model DFS L-Vent / Type B Gas Vent Installation Instructions", Selkirk Corporation, 5030 Corporate Exchange Blvd., Grand Rapids MI 49512, Tel: 800-433-6341 & Selkirk Canada Corporation, PO Box 526, Depot 1, Hamilton ON L8L 7X6, 888-735-5475, web search 10/15/2010, original source: www.mass.gov/Eeops/docs/dps/780%20CMR/780068.pdf
"Type L Temperature Venting Systems [on file as L_Vent_Metal_Fab.pdf] - ", Installation and Maintenance Instructions, Metal-Fab Inc., PO Box 1138, Sichita KS 67201, 316-943-2351, Email: firstname.lastname@example.org website: www.mtl-fabinc.com
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. 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: 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.
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