Crushed flexduct no liner (C) Daniel Friedman Duct Damage: Mechanically-damaged HVAC Ducts
HVAC ducts damaged by crushing, flooding, mechanical cleaning

  • DUCT DAMAGE, MECHANICAL - CONTENTS: Photo guide to types of damage to HVAC air ducts - mechanically damaged heating or air conditioning ducts, especially flex ducts, may have more than one cause and effect. Air Conditioning (or Heating) Duct Defects, Defective air duct products and materials. Damaged duct insulation increases heating or cooling system operating cost.
  • POST a QUESTION or READ FAQs about the types of damage found in HVAC air ducts

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Mechanically-damaged HVAC ducts:

This article describes damaged HVAC ducts due to some mechanical activity such as stepping on a duct and crushing it, or improper and too-aggressive duct cleaning methods that damage duct interior surfaces, liners, or binding resins. While metal ductwork can usually be cleaned successfully, fiberglass-lined HVAC ducts and flex duct are likely to be destroyed by aggressive, mechanical cleaning.

This article series discusses duct system defects such as missing air conditioning cool air supply or return air registers, undersized air conditioning duct openings, improper cooling duct routing, cooling (or heating) air duct corrosion, leaky air duct connections, defective heating or cooling ductwork materials such as Goodman gray flex-duct, some Owens Corning Flex-duct, and asbestos-containing air conditioning or heating duct work.

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Photo Guide to Damaged HVAC Air Ductwork

Crushed flexduct no liner (C) Daniel FriedmanArticle Contents

[Click to enlarge any image]

At left our photo, provided by reader Steven King, shows the interior of fiberglass-lined flexduct that has been crushed, perhaps by having been stepped-on?

The result is reduced heating or cooling air flow, reduced building occupant comfort, and higher heating or cooling system operation cost.

Most flex duct has a plastic or mylar liner in the duct interior and does not show exposed fiberglass as in Mr. King's photo.

Damaged Flex-Duct

At the above example of crushing flex duct we were also concerned that the exposed fiberglass in the duct appears to have been mechanically damaged, perhaps by a too-aggressive attempt at duct cleaning that may result in higher levels of airborne fiberglass duct insulation fragments in the building.

Other crimping and blockage or support problems found in flexduct installations are discussed

Damaged blocked combination of fiberglass flex duct & metal ductwork

Crushed flexduct no liner (C) Daniel Friedman

This photo shows the connection of fiberglass flex duct to a metal HVAC duct component. The fiberglass flex duct has been badly damaged.

As this photograph of duct damage was taken at the same installation as the example above, we suspect that an inexperienced duct cleaner has been at work here.

Other examples of flex-duct damage are at ALLOY SYSTEMS FLEXDUCT, OWENS CORNING FLEXDUCT, and OWL FLEXDUCT where we describe loss of the plastic duct exterior or interior liner.

Water flooding in ductwork also ruins it and is discussed at WET CORRODED DUCT WORK and at WATER & ICE IN DUCT WORK

Rust damage to HVAC air duct systems

Photo of severe rust damage to return air duct

The rusted out duct photo at left shows a common return air duct system in some older homes: space between the floor joists was used as an air passage, sometimes also for supply air.

But when the metal sheeting nailed across the floor joist bottoms has rusted out, severe air leaks occur.

In a supply duct the result is higher heating or cooling costs. In a return air duct a hole such as the one shown in our photo can cause unhealthy or unsafe conditions by drawing other unanticipated air into the duct system (in this case next to a crawl space vent we are basically heating outdoor air and blowing it into the living area).

At below right we illustrate the rust (and rodent infestation) found in an in-slab metal spiral air duct.

SLAB DUCTWORK - catalogs the functional and environmental problems found when HVAC air ducts are routed in or below floor slabs

Watch out: large improper openings in return ductwork, whether from rust or any other causes, can cause building backdrafting and dangerous carbon monoxide hazards.


Water and rodents in air duct (C) D FriedmanSee RETURN DUCT AIR LEAKS

and SUPPLY DUCT AIR LEAKS for additional examples of these problems.


Other Duct System Damage Topics are listed in the links listed at the "More Reading" links at the bottom of this article under
DUCT SYSTEM & DUCT DEFECTS; some of those links are described below.

Water and rodents in air duct (C) D Friedman

Illustrations of a leaky cast iron sewer line that sent sewer gases into the building's transite (asbestos cement) heating duct system can be seen

Damaged or Lost HVAC Duct Exterior Insulation

Reader Question: is this normal wear on the insulation on my duct work? Should I be worried about mold contamination?

HVAC ducts lost insulation (C) InspectApedia HVAC ducts damaged  insulation (C) InspectApedia

Had an insulation question. Hopefully you are able to view the attached pictures. Do you think this is normal wear to the insulation around the Duct work or should I be concerned about the possibility of mold contamination? - J. 3/31/2014


I'm not sure what I'm looking at in your photos but it looks as if fiberglass insulation has been lost around the outside of galvanized metal HVAC ductwork.

If that's so the results are increased operating costs & risk of in-duct condensation and moisture-related problems (mold for example).

If your HVAC system ductwork used fiberglass on its interior and that has been damaged, see DUCTS DAMAGED DURING CLEANING.

For a discussion about whether or not you can find mold in fiberglass - yes -

and see

Causes of mold growth in HVAC ductwork - mold in air ducts
at WHY DOES MOLD GROW in INSULATION? for a discussion of possible mold growth in fiberglass insulation in general.

Generally if I see ducts like this I expect that all of the original installation was on the duct exterior - where it doesn't produce much of a particle hazard to air flowing inside the ducts except in the event of duct leaks in the return air system.

Hazards of Un-Lined or Raw Fiberglass-Lined HVAC Ducts

Reader Question: Un-lined Flex Ducts Exposes Fiberglass in My Home - is this OK?

Flex duct appears to be missing liner (C) Daniel Friedman

I have some pictures that I think you maybe interested and perhaps help others determining what is happening or has happened to the flexduct.

It is similar to the ones above but have a clearer view.

Some only have an est. 6 in wide strip of inner lining or none at all.

I want to know if an inner lining should exist or not?

Did the inner lining erode?

Is it a manufacture defect or faulty installation work?

I have attached my photos. You are welcome to use them on your website if it can help someone. Perhaps, it could help someone properly come to a conclusion and solution. Your assistance and help would be greatly appreciated. Sincerely, - A.G. 10/11/2012

Reply: Cleaning, Maintenance, Repair/Replace or Re-Line Suggestions for Un-Lined or Incompletely-lined Flex-Duct

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with an HVAC system, duct work, or often other more urgent building concerns that an owner or occupant may not have noticed. That said, I have taken a look at your photos and from what I can see:

Flex duct appears to be missing liner (C) Daniel Friedman Flex duct appears to be missing liner (C) Daniel Friedman

Yes, normally flex-duct used in HVAC systems includes a plastic or vinyl interior liner and an external cover as well, leaving the fiberglass duct insulation sandwiched between the two. In my OPINION and based on your pictures

My recommendations for un-lined HVAC flex duct:

Fiberglass HVAC Ducts Damaged by Mechanical Cleaning

Fiberglass-lined HVAC ducts badly damaged by mechanical duct cleaning (C) Fiberglass-lined HVAC ducts badly damaged by mechanical duct cleaning (C)

[Click to enlarge any image]

Question: did my duct cleaning company ruin my ductwork by using a mechanical cleaner?

Here are photos from inside the main heating duct showing damage from duct cleaning. Some were taken from the end of the duct and others from a removed vent. - Anonymous Reader-contribution 2016/11/05


The ducts you show are a mess and beyond economical repair. You'll want to see every foot of ductwork as it would make no sense to do only a partial repair.

See DUCT CLEANING ADVICE for details about the problem of damage to ducts during duct cleaning.

Reader follow-up:

FYI, the duct cleaning company sent a tech to inspect the damage to the main heat duct (which my local HVAC co estimated at $2500.00 to replace). Surprisingly, the duct cleaning co. is sending a contractor to replace the duct, including an insulation wrap - outside this time. - Anonymous, 11/11/2016


Continue reading at DUCT ROUTING & SUPPORT or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see BLOWER LEAKS, RUST & MOLD explains causes of leaks & mold in HVAC ducts

Or see DIRTY A/C BLOWERS includes leaks, rodents, & mold in air handler units





Or see WHY DOES MOLD GROW in INSULATION? that includes photos and test results examining suspected mold on the surface of fiberglass-lined HVAC ductwork.

Suggested citation for this web page

DUCT DAMAGE, MECHANICAL at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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