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DUCT SYSTEM DEFECTS - Heating and Cooling Duct Work Inspections for Adequacy, Safety, Defective Materials, Asbestos, Mold AirCondAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• Air Conditioning (or Heating) Duct Defects
• Defective duct products and materials
• Duct installation defects, safety hazards
• Return air adequacy

This chapter of "How to Inspect the Central Air Conditioning or Cooling System" describes the inspection of the registers and zone components of heating and air conditioning (HVAC) duct systems for 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. Also see our explanation of problems with reduced air flow, dirty air handler blowers, blocked cooling coils, blower leaks and mold, frost and ice build up in ducts, and blower sizing problems of air condtioning retrofit projects which we discuss at: AIR HANDLER UNIT, see our discussion of LOST COOLING CAPACITY and see our discussion of various problems with AIR FILTERS for HVAC SYSTEMS since all of these can involve diagnosing and curing problems with the adequacy of distribution of cool air in a building. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

This chapter continues with a discussion of common defects found in air conditioning duct work such as incomplete supply or return ducts, poor choice of location or size for supply and return registers, locating ducts in problem areas, leaks into and corrosion of duct work, leaky duct connections, and special notes on product failures by two manufacturers of flexible duct work. The chapter concludes with important safety warnings about dangerous openings in duct work.

Air conditioning duct system defects include a remarkably wide range of errors, from failure to supply cool air or failure to even circulate air in the building, to health hazards such as use of asbestos material in or on duct work, to very dangerous conditions such as drawing heating equipment combustion gases into the building cooling (or heating) air.

The master document, of which this is a chapter, describes the inspection of residential air conditioning systems (A/C systems) to inform home buyers, owners, and home inspectors of common cooling system defects. Asbestos in or on HVAC ducts is a possible hazard for which we provide links to a separate document - see "Asbestos HVAC Ducts" at below left.

Scroll down or use the links at left to continue reading about duct defects with the next section: registers and zones.

More Reading:
Asbestos as a duct hazard is discussed at ASBESTOS HVAC DUCTS.
Fiberglass in HVAC ducts is discussed at Types of Duct Work using fiberglass materials and at risk of mold contamination are discussed here.
Mold in the air handler or duct work is discussed at AIR HANDLER UNIT chapter
HOW TO PREVENT MOLD: Correct the Causes of Mold and Prevent Indoor Mold or other indoor environment problems
OPTIMUM INDOOR AIR QUALITY - Air Filter Choices & Placement for Optimum Indoor Air Quality

Air Conditioning (or Heating) Duct System Condition & Health/Safety Hazards

UNSAFE OPENINGS - Air Conditioning or Heating Duct System May Draw Dangerous Combustion Gases

Return air collected close to gas-fired appliance: This poorly-designed central air conditioning return duct was located in a cramped basement boiler room only five feet from a large gas-fired, natural draft heating boiler. It is a possible safety concern. When the location of the system return air duct work and air handler is such that the system may pull dangerous flue gases back out of the gas appliance flue vents, piping and into the building heating or cooling air we cite it as a potential hazard: distribution of combustion gases may be blown into the living area. This is a dangerous carbon monoxide hazard. Such a system should be examined promptly and corrected by a qualified heating professional.

Flue gas and carbon monoxide safety hazards caused by duct openings near heating equipment: Still more common is the presence of extra openings cut into the return ducts atop a building furnace (perhaps also serving as the air conditioning blower system in cooling season). Often these openings are added to provide more return air to a system which is not providing sufficient cooling or heating to the building. But return air openings right at a heating appliance risks drawing combustion gases into the building air supply as well as potentially interfering with proper appliance draft and combustion. This is the case particularly with gas fired furnaces, boilers, or water heaters, which operate at a lower and usually natural draft, but it is also a potential safety hazard with oil-fired equipment.

Flue gases from nearby heating or water heater appliances are easily drawn into the return air plenum and air handler. This would permit circulation of flue gases into the living area and can be a safety hazard which could deliver potentially fatal carbon monoxide to building occupants.

Return air openings close to natural-draft fired appliances, again particularly gas, can also interfere with proper gas (and possibly oil) burner operation by competing for combustion air, thus causing carbon monoxide production when the burner is operating.

If openings are found in the duct system near fossil-fuel fired appliances it should be reported as an indication of a system operating problem (inadequate return air) and as a safety hazard (potentially fatal carbon monoxide poisoning). Review this potential hazard with a qualified service professional. For example, should a stack pipe fail and flue gas be dumped into the furnace room it would be picked up and distributed throughout the building.

Sample inspection report language:
*** Safety Hazard - additional details: when the heating system [or air conditioning system] is running and/or when other nearby heating equipment is running (such as a water heater) there is negative pressure around the furnace [or air handler unit] and at this return air inlet register, (demonstrated during our inspection by seeing the furnace blower pull the utility room door shut) risking pulling dangerous flue gases such as carbon monoxide out of the flue vent pipe and into the building heating air through the barometric damper or through other openings in the vent piping. This item should be handled as soon as possible by an experienced and qualified heating professional - carbon monoxide poisoning is a potentially fatal safety concern.

ASBESTOS HVAC DUCTS - Asbestos Materials on or in the Air Conditioning or Heating System Duct Work

The identification of asbestos materials on HVAC ducts and flue vents is discussed in depth, where we provide field identification photos to assist in the recognition of asbestos containing materials on heating and cooling systems, at ASBESTOS HVAC DUCTS & FLUES

Also see Asbestos: visual identification of asbestos-suspect materials in buildings - a photo guide.

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AIR CONDITIONING SYSTEMS Chapter Index

To continue reading this air conditioning inspection guide, use links to the document chapters at left or below. Links shown in green font indicate where you are in this document.

Technical Reviewers

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