Metal chimney at rooftop (C) Daniel Friedman Metal Chimneys & Flues: Inspection, Diagnosis, Cleaning & Repair Guide

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This article describes the types of manufactured metal chimneys. We explain the difference between Class-A Chimneys, Metalbestos chimneys, Type B Vents, Type L Vents, Triple Wall metal chimneys, and Super Chimneys, 629 Chimneys, and 650-C Chimneys.

Each of these chimney types has specific intended uses, fire clearances, and installation requirements. Improperly-installed chimneys, use of the wrong chimney type, or failure to properly maintain the chimney are likely to lead to unsafe conditions and risk a building fire.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Metal Chimneys & Flues: Types, Codes, Installation Requirements

Metal chimney at rooftop (C) Daniel FriedmanTypes of Metal Chimneys and Metal Vents

Our page top photo shows a remarkable number of metal chimneys (at least 24) on a Duluth Minnesota building. Can you explain it?.

The metal faux-chimney top shown in our photo is being inspected by an ASHI Headquarters staff member during a Chicago IL field trip.

Disassembly would be required to know much about the interior of this chimney, but from the exterior we can inspect for

Without more information we cannot see for sure just what kind of metal chimney terminates in the chimney cap shown by our ASHI Staff person.

List of Manufactured Metal Chimney Types

Here are the principal types of manufactured metal chimneys. We discuss each of these in the articles linked-to below.

Metalbestos chimney cleanout © D Friedman at

Metal chimney and flue: types, clearances, installation, inspection, fire hazards

Metalbestos chimney cleanout © D Friedman at

Question: Metalbestos stove pipe fire clearances: roofing mastic was blobbed around our metalbestos chimney

I have an 8 inch Metalbestos™ stove pipe going through an open beam ceiling, with an avalon wood stove.

My question is how hot does the outside of the metalbestos pipe get on the roof in the area of the stove pipe flashing, its a reddish rubber boot style?

The reason I am asking is a roofer installed a new metal roof and rubber boot flashing and cut the back side of boot to get it to fit then patched it with a black sticky flexible flashing, with flash point of 201 degrees. Thanks - R.W.

Our photo (left) shows a Class A "Metalbestos™ type chimney at a low slope EPDM roof penetration - not the chimney penetration in the reader question described above. Photo courtesy Galow Homes.

Reply: Follow the manufacturer's instructions for air spaces and chimney clearances

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem or identify fire clearance and chimney safety issues including the one you raise. But when workmanship is amateur or incomplete, keep in mind that the same installer may have made other errors.

That said, here are some things to consider:The temperature that you will find on the outside of the metalbestos chimney pipe varies from cold (not in use) to warm (in normal use) to potentially higher, depending on what fuel is being burned, distance from the fire source, conditions in the chimney, and other variables.

Example of an insulated metal chimney surface temperature

At a new Class "A" insulated metal flue venting an oil fired heating boiler and located about 35" from the flue vent connector atop the boiler and with the boiler at operating temperature (about 450 degF inside the flue vent connector at the boiler top) the outside temperature of the metalbestos chimney was "hot" to the touch but less than 200 degF.

But because of the variables involved that cause variation in metal chimney surface temperatures, I'm not sure anyone could quote a specific number to answer your question.

You will find in the metal chimney installation instructions (and perhaps your local building codes) that the manufacturer wants 2" or 2 1/2" air space clearance between the Class "A" chimney sections and any nearby combustibles.

So if your roofer put combustible roofing mastic against a Class-A chimney chimney s/he has probably violated the instructions and possibly local and national building codes.

Single metal flue through a barn wall north of Duluth (C) Daniel FriedmanDetails about fire clearances for different types of metal flues and chimneys are found

Readers of this section should also


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.This article explains the types, uses, characteristics, and installation requirements for different classes of metal chimneys.

All of these metal chimneys use multiple-walled metal pipe; some products add a fire-proof insulating material between the walls of the chimney pipe while others rely on air space.

Single-wall metal pipes used to connect heating appliances to chimneys (metal or masonry) are discussed separately
at Single-Wall Metal Flue Vent Connectors where we provide details about single wall metal flues and their fire clearance requirements.

The installer of the single wall metal chimney (probably venting a woodstove) observed on this Minnesota barn on Highway 61 north of Duluth had to go to some trouble to clear the edges of the barn roof. This chimney made me nervous.


Continue reading at BRACING for METAL CHIMNEYS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.





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