Chimney Types & Materials - an Inspection Guide InspectAPedia® -
Types of chimneys used on buildings: masonry, various metal chimneys, flues, other materials
Detailed Inspection & Photo Guide to chimney defects: brick chimneys, concrete block chimneys, factory built metal chimneys and flues, Single wall metal flues, Type B vents, Type L Chimneys, etc.
Questions & answers about the different types of chimneys, flues, vents: materials & construction
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This article names and describes the various types of chimneys used on buildings. Our page top photo shows collapsing brick masonry chimneys taken by the author in Los Angeles, CA following the Northridge Meadows earthquake in 1994. Readers may also want to see the basic chimney definitions at Definitions of Chimney Types & Parts.
These articles on chimneys and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed. As with most inspection and safety topics, this material may be incomplete.
Masonry chimneys for low heat (less than 1800oF) in residences shall be
constructed of solid masonry, solid waterproofed modular concrete block or
rubble stone laid with full push-filled head and bed mortar joints. The thickness
shall be a minimum of 4" for brick and concrete block to 12" for rubble stone.
Fire
clay flue linings (ASTM C-315) with a 5/8" wall thickness shall line all masonry
chimneys. The flue section joints shall be fully bedded in a medium duty
non-water-soluble calcium aluminate refractory mortar with a smooth surface
inside the flue. An air space of one half inch to one inch maximum shall separate
the flue liner from the masonry with only enough mortar to be used to make a
good joint and hold the tiles in position.
Notice the unlined flue at the top of this page? It is a single wythe or "one brick"
thick. If those bricks are less than 4" wide the chimney is not in compliance
with modern codes. Its condition is very important since loss of mortar or
a chipped brick can be a fire or gas hazard.
Below we define the basic types of chimneys used to vent various types of heating appliances and devices. For more detail about each chimney type, construction, inspection, fire clearances, rooftop height requirements, etc. see the links at page left or at the end of this section of text.
Factory Built Chimneys
Several types of factory manufactured chimneys are in use for residential
situations.
They are a Pre cast Pumice Masonry unit that stacks together, a Form
Filled Refractory Cement stack unit, a Stainless Steel Double or Triple Wall air
insulated sectional unit and a Combination Air and Ceramic Fiber insulated triple
wall unit.
List of Manufactured Metal Chimney Types
Here are links to detailed articles about each of the principal types of manufactured metal chimneys. We name each of these types in text below this list, and discuss each of these in the articles listed. Readers may also want to see the basic chimney definitions at Definitions of Chimney Types & Parts.
Single-wall metal shall be galvanized sheet steel not less than .0304" thick
or other approved, non combustible, corrosion resistant material. Limitations
require all lengths of single wall vents to be exposed from the draft hood up to
the roof or wall thimble. see Flue Vent Connectors.
Double-Wall Metal, Type B and Type L Chimneys
Type B (550oF) metal vents are a pipe within a pipe with air space
between the two walls. The inner wall is aluminum to resist corrosion and the
outer wall is galvanized steel for strength.
Type L (1000oF) metal vents use stainless steel for the inner pipe for higher
temperatures. see Type B-Vents and Type L Vents.
High Temperature Plastic Chimneys and Vents for Gas Appliances
Single wall plastic pipe (450oF) is listed to be used with condensing gas
appliances.
[Note: in freezing climates, the pitch of direct-vent appliance vents
such as those using plastic vent lines can be critical. If condensate can be
produced in the vent line, the line must be pitched to drain properly - usually
inside to a drain - so as to avoid dangerous flue blockage by ice.-- Ed.] See PLASTIC HEATER VENT and PLASTIC VENTS Goodman HTPV RECALL.
Chimney and Fuel-burning Device Categories vs. Chimney Requirements
National standards committees organized gas appliances into four
categories based upon the flue gas temperatures and pressures.
Category I is non-condensing, negative flue pressure, draft hood, AFUE
65% - 83%, vents of Type B, single-wall metal or lined masonry chimney. Mid-
efficiency, fan assisted appliances are also in this category.
Category II have negative flue pressure with a lower flue gas temperature
and require a corrosion resistant vent.
Category III is non-condensing, positive flue pressure, AFUE 78% - 83%,
vents of air tight high temperature plastic or air tight single wall metal.
Category IV is condensing, positive flue pressure, AFUE 90%+, vents of
air tight high temperature plastic, PVC or CPVC.
New Vent Requirements
Minimum vent sizes for fan assisted appliances to limit condensation and
maximum vent sizes to avoid positive vent pressures for fan-assisted appliances
are design features of the venting tables.
Draft Hood Appliances
Hot gases rise and draft upward into the chimney. The draft hood allows
dilution air to vent and mix with the flue gas which reduces the humidity or
dew point and thus reduces chances of corrosion. The dew point in a gas vent is
about 90oF to 130oF.
Mid-Efficiency Appliances
A fan assisted system reduces dilution air in the vent with the following
effects on vent performance.
Vent gas dew point temperatures (or humidity) are higher.
Less gases flow through the vent.
There is less airflow through the appliance when the unit is off.
Higher dewpoints requires that the vent warm up above the dew point to
stop condensation. However, the lower volume of gases flowing into the vent will
make it more difficult to raise the temperature. This results in more condensation
in the vent system. Oversized flues, especially on exterior chimneys, never warm
up in cold weather.
High Efficiency Oil or Gas Burning Appliances
These systems have positive pressure sealed vent/combustion air control.
The vent connectors are plastic pipes usually vented through the sidewalls of a
basement or utility room with design limits on the length and number of elbows.
Installation requires reverse pitch on the vents so that condensation can flow
back to the float trap drain.
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Additional technical contributors & reference sources for this article are listed below.
Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
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 ap@octoberhome.com
Roger Hankey is 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 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
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.
GAMA -
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.htm. 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
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
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 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
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
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