Metal chimney flue fire hazards:

This article describes various metal chimney & vent hazards which can be detected indoors in buildings: unsafe fire clearances, improper chimney slope, wrong materials, metal flues which are not continuous and excessive angular offset in metal chimneys, making them clog-prone and difficult to clean.

Other indoor damage or hazards involving metal chimneys include mechanical damage, rust, and improper installation.

Metal Chimney & Vent Indoor Hazards

Un-Licensed to Kill: An Example of a Dangerous Metal Chimney & Gas Appliance Venting Installation

- David Grudzinski

The buyer of a commercial strip plaza with 2 apartments above was required to obtain an inspection of the apartments only by the bank.

Normally commercial properties are not always required to have a pre-purchase building inspection, but this lender demanded that at least the rental apartments be inspected. That decision may have just saved some lives.

The seller purchased and installed a [used] gas fired radiant heater from a second hand outlet.

The unit was installed by the seller, who did not pull permits, did not get an inspection by city officials or the fire dept, and did not install C/O detectors in the rental units, as required by law since 2006.

See details at CO DETECTION OPTIONS

and CO ALARM CAUSES

The heating unit was installed with single wall vent pipe, through a wall without the required wall thimble that prevents contact with combustibles. [Photos above]

The vent pipe enters attic space [below left], this requires double wall pipe to prevent condensation, and not only was there no double wall pipe, the installer used metal flex pipe and he went down out the soffit instead of up through the roof.

The vent pipe was in direct contact with old dried balloon framing [photo above right], with personal storage, and clothes. When I observed the set up I was stunned.

I made it very clear that this heating unit is a very dangerous set up and can very easily cause a fire, and deadly carbon monoxide levels to accumulate.

See details at FIRE CLEARANCES INDOORS

The unit should be disconnected, and installed by a licensed heating contractor.

More questions about this gas heater installation

In addition there appears to be an immediate and lethal carbon monoxide hazard. We are guessing from the photos that this unit vents by natural draft. That is, there is no power vent.

But look at the slope on the metal chimney running through the attic: it slopes down rather than up - if this is natural-draft heating equipment there will be no draft - a condition that produces dangerous carbon monoxide that can quickly prove lethal.

See details at CARBON MONOXIDE - CO

We also had a question about the flue vent materials; if aluminum material was used there are additional hazards and code violations.

David Grudzinski, Advantage Home Inspections, ASHI cert # 249089, HUD cert# H-145, is a professional home inspector who contributes on various topics including structural matters. Mr. Grudzinski, Cranston RI serving both Rhode Island and Eastern Connecticut can be reached at 401-935-6547 fax- 401-490-0607 or by email to Davidgrudzinski@aol.com. Mr. Grudzinski is a regular contributor to InspectAPedia.com - see DECK FLASHING LEAKS, ROT Case Study, and BASEMENT WATER MOLD IMPACT and VERMICULITE INSULATION for examples.

Metal Chimneys Must be Continuous

Carson Dunlop's sketch shows a metal chimney that is not continuous from the heating appliance up through the roof.

An installer may install a metal flue through only part of the building, deliberately as shown in the sketch, thinking that the heat from the indoor section of the metal chimney will give extra heat to the upstairs in the building.

The result is a hybrid chimney with two flues which are offset from one another.

Not only is it difficult to clean these hybrid flues but the risk of creosote build-up and a chimney fire is increased.

Excessive Offset from Vertical in Metal Chimneys

Carson Dunlop Associates [at REVIEWERS] sketch below shows a metal chimney that has excessive offset in it travel upwards between the heating appliance and the roof.

The allowed angular offset in a chimney is as much as 60 degrees in some but not all jurisdictions.

As with our description of discontinuous metal chimneys above, a concern is with creosote build-up n the elbows and also in the sloped section of the chimney.

Look for evidence of corrosion or creosote leakage at the joints.

Details are at CREOSOTE FIRE HAZARDS

Check with your local building code and fire officials about the chimney offset angles allowed in your area.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: wood stove chimney clearance clarification

(Aug 23, 2014) Dino said:
Wood stove requires 27 inches between vent pipe and combustable. Does that require the pipe from the roof through the ceiling have that clearance or can it be closer and use elbows to get out to the 27 inch? It will be at least 18 inches away from the wall at the cathedrial ceiling.

Reply:

Dino,

You'll want to use a "zero clearance" ( which may mean one-inch) insulated metal chimney for passing through combustible materials such as ceilings, walls, roofs. Check with your local fire marshall or code inspector too. Wood stove installations require a permit and inspections in most jurisdictions. As soon as you call for help you've got the inspector on your side where s/he may have other helpful tips for meeting code and avoiding a fire.

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

Or see these

Metal Chimney Articles

• CARBON MONOXIDE - CO
• CHIMNEY FIRE ACTION / PREVENTION
• CHIMNEY HEIGHT & CLEARANCE CODE
• CHIMNEY STAINS, INDOORS
• CREOSOTE FIRE HAZARDS
• FIRE CLEARANCES INDOORS
• FIRE CLEARANCES, METAL CHIMNEYS
• METAL CHIMNEYS & FLUES - home
• METAL CHIMNEY INSTALLATION MANUALS
• METAL CHIMNEY CONNECTIONS

Suggested citation for this web page

METAL CHIMNEY & VENT INDOOR HAZARDS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to CHIMNEYS & FLUES

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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