Unsafe gas appliance vent and chimney installation(C) InspectAPedia David Grudzinski Metal Chimney & Vent Indoor Hazards

  • METAL CHIMNEY & VENT INDOOR HAZARDS - CONTENTS: Discontinuous metal flues, bad fire clearances, wrong materials, wrong slope, carbon monoxide dangers, excessive offset from vertical, indoor details reveal unsafe metal chimneys
  • POST a QUESTION or READ FAQs about metal chimney defects and safety problems that can be detected by an inspection of the building interior

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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.

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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.

Unsafe gas appliance vent and chimney installation(C) InspectAPedia David Grudzinski Unsafe gas appliance vent and chimney installation(C) InspectAPedia David Grudzinski

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. (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.

Unsafe gas appliance vent and chimney installation(C) InspectAPedia David Grudzinski Unsafe gas appliance vent and chimney installation(C) InspectAPedia David Grudzinski

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. (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. (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 Mr. Grudzinski is a regular contributor to - see DECK FLASHING LEAKS, ROT Case Study, and BASEMENT WATER MOLD IMPACT and VERMICULITE INSULATION for examples.

Metal Chimneys Must be Continuous

Discontinuous metal chimney (C) Carson Dunlop Associates

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.

Excessive metal chimney offset (C) Carson Dunlop Associates

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. (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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