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Photograph of a cracked chimney top crown and no cap installed. Chimney Types & Materials

Guide to types of chimneys found on buildings: this article names and describes the various types of chimneys used on buildings.

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. Our page top photo shows collapsing brick masonry chimneys taken by the author in Los Angeles, CA following the Northridge Meadows earthquake in 1994.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Chimney Types and Chimney Construction Materials

The remarkable chimney shown at left was home made by a building owner who used an aluminum light pole for this purpose.

Watch out: this is not a safe nor approved chimney installation. It's creative, though. The photograph was contributed by frequent InspectApedia.com commentator NHFireBear who remarks:

NH Fire Bear adds wisdom on Chelan's comments

As reader Chelan mentioned in a comment in this article's FAQs, under NFPA 211, single-wall pipe is not allowed for "chimneys" of one- or two-family dwellings, although may be used as connectors, i.e., between the appliance and the chimney, provided it is NOT "galvanized steel pipe" for a solid-fuel-burning appliance connector. NFPA 211:12.4.1.2

Here is a photo of the situation where a person used a surplus light pole, made of aluminum, as a connector and a chimney for a wood stove in a garage, without the necessary 18-inch clearance and no permit. It was later replaced with a proper insulated system with proper clearances when they applied for a permit to use the building as a dwelling.

Points for creativity, but possibly a dangerous thing to do when you're a long way from the volunteer fire station!

See SINGLE WALL METAL VENTS & CHIMNEYS for a discussion of single-walled metal chimneys and vents. Also

see FIRE CLEARANCES, FLUE VENT CONNECTORS - separate article. Flue vent connectors not chimneys but rather single-wall metal pipes used to connect a heating appliance to a chimney.

Article Series Contents

Description & Performance Specifications of Types of Masonry and Clay Tile Chimneys

Photograph of a cracked chimney top crown and no cap installed.Masonry chimneys (brick, masonry block, concrete block, cinderblock, concrete or stone 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.

[Click to enlarge any image]

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 listed at the ARTICLE INDEX the bottom of this article or at the end of this section of text.

See complete details beginning

at MASONRY CHIMNEY GUIDE

Definitions & Specifications of Types of Factory Built Chimneys

Collapsing metalbestos insulated chimney (C) Daniel FriedmanSeveral 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.

Single-Wall Metal Pipe Chimneys or Vents

Watch out: while single wall metal flue vent pipe connectors are permitted to connect a heating appliance to a chimney, these are technically not "chimneys" but flue vent connectors and they must be installed with proper clearance from combustibles.

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.

Actual chimneys can not be constructed of single wall metal flue material.

See SINGLE WALL METAL VENTS & CHIMNEYS for details.

See FIRE CLEARANCES, FLUE VENT CONNECTORS for details about the required fire clearances.

Wood framed chimney chase surrounding factory built metal chimneys (C) Daniel FriedmanDouble-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-VENT CHIMNEYS

and TYPE L VENT CHIMNEYS for details

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 PLEXVENT ULTRAVENT RECALL

and PLASTIC VENTS Goodman HTPV RECALL. for details about these safety recalls

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.

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.

  1. Vent gas dew point temperatures (or humidity) are higher.
  2. Less gases flow through the vent.
  3. 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.

Readers may also want to see the basic chimney definitions at .

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: NFPA 211 (2010) prohibition of single wall metal chimneys in or outside of one and two family dwellings.

(Sept 9, 2014) Chelan said:

NFPA 211 (2010) section 8.1.1 prohibits use of single-wall metal chimneys inside or outside one- and two-family dwellings, so would that be a condition that a home inspector should point out?

Reply:

Chelan, yes, I agree with your surmise as does NH Firebear - see his comments and a remarkable aluminum light pole chimney shown at the top of this article.

Question:

(Nov 27, 2014) Anonymous said:
Why is one flue capped off at the top withcement on my double flue chimney?

Reply:

Anon the flue should be capped ONLY if it is not in use - that step keeps animals from making a home therein and also avoids water or rain damage to the flue and chimney.


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Continue reading at CHIMNEY DEFINITIONS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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CHIMNEY TYPES & MATERIALS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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INDEX to RELATED ARTICLES: ARTICLE INDEX to CHIMNEYS & FLUES

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