Metal chimney not Type B Vent (C) Daniel Friedman Single-Wall Metal Vents and Chimneys: Inspection, Diagnosis, Cleaning & Repairs

  • SINGLE WALL METAL VENTS & CHIMNEYS - CONTENTS: Detailed Inspection & Photo Guide to single wall chimney defects. Obsolete single wall metal fireplace chimneys. Unsafe, damaged single wall metal chimney used for venting a gas appliance.
  • POST a QUESTION or READ FAQs about single wall metal chimneys & flues: installation, fire clearances, troubleshooting, maintenance

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Single wall metal chimneys:

This article describes Single-Wall Metal Vents and Chimneys, their Inspection, Diagnosis, Cleaning & Repairs.

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Single-Wall Metal Vents and Chimneys

The single wall metal fireplace chimney shown at page top and shown again at below left was installed in a solid masonry fireplace in the 1960's.

It can no longer be safely used because of the new construction in the left of the photo. As you can see at below right, a building addition constructed close to the original single wall metal chimney has left it too close to the new structure. [Click to enlarge any image]

Single wall metal fireplace chimney above a flat roof, built ca 1970 (C) Daniel Friedman Single wall metal fireplace chimney above a flat roof, built ca 1970 (C) Daniel Friedman

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:

This chimney will need to be replaced with a modern insulated flue and extended in height. As long as the fireplace is not used, that corrective measure can be deferred.

Metal chimney not Type B Vent (C) Daniel FriedmanThe metal chimney shown at left is not a Type B gas vent and may be unsafe. Certainly it should not be in use for venting a heating appliance.

Do not mistake this single-walled vent for a Type-L vent nor for a Type-B vent even though a hasty glance may make it look like one of those.

This vent appears to be single-walled aluminum and it has what looks almost like a coffee can installed as a rain cap.

If the metal chimney we see in this photo is being used to "vent" a water heater it is probably not working and probably lacks adequate draft. The result may be carbon monoxide release in the building.


The very tall single wall metal chimney shown at left is located on a building in Manhattan and was photographed from the Lotus Club. Several stories tall you can see that the chimney is braced about every 12-feet, and is askew, loose, and rusty.

This chimey was so tall I could not photograph the entire structure in one image.

Tall rusty single wall vent (C) Daniel Friedman

As a single walled chimney in a cold climate venting gas fired equipment, one might question its venting efficacy. In turn, condensation from poor venting might be a factor in that rusting.

Below: a single-walled metal flue extending through the wall of a barn that has been converted to a welding shop and sales facility on Highway 61 north of Duluth, Minnesota.

Single metal flue through a barn wall north of Duluth (C) Daniel Friedman

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.

Unsafe single wall metal chimney made from an aluminum light pole (C) NHFireBearSingle wall metal pipes are also described in our table listing clearances by gas-fired appliance type
at Listed Flue Vent Connectors for Gas Fired Heating Appliances.

Also see Metal Chimney Safety Alert - CPSC Document #5047.

Readers of this section should also be sure to review details

This article series on chimneys, chimney construction, 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.

The remarkable single walled metal chimney shown at below-left was constructed using a "found" hollow aluminum electric lighting pole and is discussed by NHFireBear at CHIMNEY TYPES & MATERIALS

Dangerous Modifications to Single Wall Metal Chimneys & Flues, Passing Through the Metal Flue

Single wall metal flue interrupted by handrailing (C) Daniel Friedman Oxaca Mexico

Above: at this single wall metal chimney installed at a restaurant in Oxaca, Mexico, we noticed that the chimney installer and the handrail installer simply could not find an accord. Shown below in a closer look, the handrailing passes right through the chimney. Both the handrail and the chimney are unsafe.

Single wall metal flue interrupted by handrailing (C) Daniel Friedman Oxaca Mexico

For handrailing enthusiasts see HANDRAIL CONTINUITY


Continue reading at FIRE CLEARANCES INDOORS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.





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