DUCT SYSTEM DEFECTS - Heating and Cooling Duct Work Inspections for Adequacy, Safety, Defective Materials, Asbestos, Mold
InspectAPedia^® -

Air Conditioning or Heating Air Duct Defects: how to inspect, find, diagnose, and repair problems with air ducts on HVAC systems
Diagnostic List of Heating & Cooling Air Duct Defects: Things to Inspect, Check, Repair, or Replace
Defective air duct products and materials
HVAC Supply & Return Air Duct Leaks & Obstructions - Theory vs Practice
Heating & Cooling air Duct installation defects, safety hazards
Return air adequacy or lack of return air can prevent adequate warm or cool air flow in a home
Questions & Answers About Air Duct & Air Flow Problems on Heating & Air Conditioning Systems

Defects in HVAC duct systems: this article explains how to inspect and diagnose trouble with heating or cooling air flow, air ducts, air registers and zone components of heating and air conditioning (HVAC) duct systems. This diagnostic article describes common defects found in HVAC 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 article includes important safety warnings about dangerous openings in HVAC duct work.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

Diagnostic List of Heating & Cooling Air Duct Defects: Things to Inspect, Check, Repair, or Replace

We explain how to find and correct air duct problems 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 conditioning retrofit projects which we discuss at: AIR HANDLER / BLOWER UNITS, 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. Readers should also see our INDOOR AIR QUALITY IMPROVEMENT GUIDE article series.

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.

Our master list of HVAC duct system inspection, diagnosis, and repair articles continues just below and at the left of this page.

Below we list some common sources of poor air flow from air conditioning or heating duct systems: check these first before ordering a more costly survey or repair job.

HVAC Supply & Return Air Duct Leaks & Obstructions - Theory vs Practice

Technical note: The D'Arcy-Weisbach equation for pressure and head loss can be used to calculate the actual pressure loss due to friction in a building piping or air duct system. The Engineering Toolbox provides the D'Arcy-Weisbach formula: Δp = λ (l / d_h) (ρ v² / 2) where Δp = pressure loss (Pa, N/m²), and l = length of duct or pipe (m) and d_h = hydraulic diameter (m) and finally, ρ = density (kg/m³).

Watch out: But keep in mind that even this apparently accurate calculation of the effect of piping on air pressure and airflow loss will not include the effects of obstructions in the building return air or supply air duct system such as

Air filter or other item that has been sucked into the duct system will block air flow and can risk a fire if drawn into the blower assembly fan, Dirty Air Filter Problems are perhaps the most common cause of unsatisfactory airflow in an HVAC system.
Blower Fan: dirty blades on a squirrel cage blower assembly fan significantly reduce the blower fan's ability to move air into the HVAC system from the return-air side as well as reducing its ability to push conditioned air into the occupied space. DIRTY A/C BLOWERS
Fire damper that has become stuck in the closed or partly-closed position interferes with proper airflow through the system FIRE DAMPERS in DUCTWORK
Flex duct defects: Collapsed sections of flex duct block or stop airflow in either supply or return air systems DUCT ROUTING & SUPPORT
Insulation loose in air ducts: Collapsed duct interior insulation, (FIBERGLASS DUCT, RIGID CONSTRUCTION
Leaks in the supply air duct system are a very common HVAC duct defect that results in poor heating or cooling air flow. LEAKY DUCT CONNECTIONS
Return air inlets: Return air inlet grilles that are obstructed with dirt, debris, or furniture or that are improperly located or are just too small mean that because the heating or cooling system is "starved for air", the supply air flow into occupied spaces will also be reduced. RETURN AIR REGISTERS & DUCTS
Transite air ducts: Crushed or collapsed transite duct TRANSITE PIPE AIR DUCTS
Zone dampers that are stuck partly closed obstruct air supply into that building area, or if stuck "open" when the zone damper should be closed, airflow to other building areas will be reduced. ZONE DAMPER CONTROLS
Also see UNDERSIZED RETURN DUCTS.

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 at TRANSITE PIPE AIR DUCTS and at CAST IRON DRAIN PIPING.

Questions & Answers About Air Duct & Air Flow Problems on Heating & Air Conditioning Systems

Question: How do I Diagnose Too Little Cool Air Flow Downstairs?

I have a 2 story house the air flows out the registers heavy upstairs but downstairs hardly any flows and from one there seems to be none. i inspected ductwork but find no visible pinching.

- Stephen

Reply: Tips for diagnosing uneven air conditioning air flow between floors in a building

Tips for diagnosing uneven air conditioning air flow:

Stephen hasn't provided much detail about how the air conditioning system in his home is designed and installed except that he doesn't see any duct pinching [DUCT ROUTING & SUPPORT], so pending some feedback we start with some general cool air flow diagnostic tips.

In a two story house at which air conditioning is provided by a single air handler, balancing the delivery of air flow can require extra attention to duct routing, use of balancing dampers in the ductwork, return air register location, and supply air register location and even multiple air filters or air filter condition.

In contrast, if the home has separate air handlers, one for upstairs and a second for downstairs his cool air flow problem would be simpler to explain.

Is this an A/C retrofit job? Just double check - if this is an A/C retrofit job onto a home that already had warm air heating, and if the A/C air handler was put in the attic, perhaps it is ONLY connected to the first floor ductwork. Rule that condition in or out first.

Stephen reports heavy air flow upstairs and poor air flow downstairs.

Check for balancing dampers [see BALANCING AIR DUCT FLOW] : since it is easier to push cool air down through ducts from an upper level to a lower level in a building than it is to push cool air upwards from lower to upper floors, the installer may have included airflow balancing dampers - look for these in the visible and accessible ductwork as well as at individual supply and return registers.
Check ductwork connections. Perhaps there are none or too few delivery ducts to downstairs? In some air conditioning diagnosis jobs we found that an air duct had simply become disconnected entirely.
Check for return air obstructions: if you are trying to blow cool air into rooms whose doors are shut and if your system uses a centralized air return register, air supply may be blocked.

Let us know what you find. It may help other readers.

Questions & Answers regarding this article

Questions & Answers About Air Duct & Air Flow Problems on Heating & Air Conditioning Systems.

Ask a Question or Search InspectAPedia

HTML Comment Box is loading comments...

Recommend / Share this Article

...

Technical Reviewers & References

InspectAPedia.com^® - Daniel Friedman - Publisher & Editor.
InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

DUCT SYSTEM & DUCT DEFECTS - see detailed links at page left

Thanks to Mark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects" section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and home inspection educator.
Thanks to Jon Bolton, an ASHI, FABI, and otherwise certified Florida home inspector who provided photos of failing Goodman gray flex duct in a hot attic.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
Engineering toolbox properties of water - http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html and email: editor.engineeringtoolbox@gmail.com web search 09/16/2010
Thanks to Scott at SJM Inspect for suggesting this EPA document and for technical editing remarks regarding our air conditioning website, SJM Inspection Service LLC, serves the entire state of CT, sjminspect.com 203-543-0447 or 203-877-4774 5/16/07
Reference: Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
Reference: Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author
Mold in the air handler or duct work is discussed at AIR HANDLER / BLOWER UNITS 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
Thanks to Chris Van Rite, Vice President Sales, M&M Manufacturing Company, 4001 Mark IV Parkway Fort Worth, TX 76106, Office (817) 348-2241 Cell (817) 825-2363 - cvr@mmmfg.com - Mr. Van rite provided the HVAC & Duct System references listed just below 2/9/2009
Consortium for Energy Efficiency (CEE) - http://www.cee1.org/resid/rs-ac/hvac_press_kit.pdf
Air Diffusion Council (ADC) - http://www.flexibleduct.org/
Static Pressure Losses in 6, 8, and 10-inch Non-Metallic Flexible Ducts, Weaver, K.; Culp, C.
Texas A&M University Energy Systems Laboratory http://txspace.tamu.edu/handle/1969.1/5275
A Study of Pressure Losses in Residential Air Distribution Systems, Bass Abushakra, Iain S. Walker, Max H. Sherman, Lawrence Berkeley National Laboratory - http://eetd.lbl.gov/ie/pdf/LBNL-49700.pdf
ENERGY STAR® Homes Technical Standards - http://www.energystarhomes.com/documents/tech_standards.pdf
ASHRAE Advanced Energy Design Guide for “Small Office buildings”, “Retail buildings” & “K-12 School buildings” available currently as a free download from ASHRAE Publications Store http://www.ashrae.org/publications/page/1604 (do not copy this PDF to networks)

How to diagnose and fix an air conditioning system that is not working

Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below. To return to our air conditioning and refrigeration home page go to AIR CONDITIONING & HEAT PUMP SYSTEMS.

If your air conditioning or heat pump system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.

A/C REFRIGERANT LEAK DETECTION: how to use a TIF5000 to detect air conditioning refrigerant gas leak
A/C DIAGNOSTIC FAQs: air conditioning system diagnostic FAQs: Q&A about air conditioner repair - a detailed air conditioning system diagnostic checklist
AIR HANDLER UNIT: problems with the air handler, air filters, and the cooling coil itself
COMPRESSOR CONDENSER: problems with air conditioner compressor/condenser units. Also see FAN, COMPRESSOR/CONDENSER UNIT for help in diagnosing and fixing problems with the outdoor compressor/condenser fan and fan motor.
A/C - HEAT PUMP CONTROLS & SWITCHES: air conditioner controls and switches - begin here if your A/C won't start. Here's an important tip: most refrigeration problems, in air conditioners, refrigerators, or freezers, are electrical, not mechanical. In air conditioning school, we used to drive out and collect abandoned refrigerators that people were tossing out during our community's spring cleanup week. Taking these appliances back into the shop we found that almost always the problem that had caused the owner to dispose of their air conditioner or freezer was in an electrical connection or electrical control. So it's worth checking out switches and controls on an air conditioner before replacing more costly components.
DUCT SYSTEM DEFECTS: problems with the air duct system, air filters, supply registers, return air registers
Fire dampers, and Heating and Cooling Air Duct Controls such as manual and automatic duct dampers, zone dampers, and fire dampers are discussed and distinguished at DRAFT REGULATORS - barometric damper
LOST COOLING CAPACITY: what to do when not enough cool air comes out of the system
- What to check first if there is no cool air or not enough cool air
- Compressor failure diagnosis: basic checks of the air conditioner compressor
- Ducts & Air Handler diagnosis: basic checks of the indoor air handler (blower), air ducts, and filter system
OPERATING DEFECTS: major air conditioning problem symptoms and how to get the air conditioning system working again,e.g. compressor or fan noises, failure to start, and inadequate cool air volume
Automatic Fire Dampers for Duct Work discusses fire safety controls - a different type of automatic duct closure device than heating zone regulators.
ZONE DAMPER CONTROLS . discusses manual and automatic air duct zone controls

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Complete List of Air Conditioning & Heat Pump Design, Inspection, Repair Books at the InspectAPedia Bookstore.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
Air Conditioning Inspection, Diagnosis, Repair, Efficiency all the basics for home owners, inspectors, new repairmen
Air Conditioning SEER - New DOE Air Conditioner and Heat Pump Efficiency Standard
Asbestos HVAC Ducts and Flues field identification photos and guide
Fiberglass: Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation
...

Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair

Ask a Question or Search InspectAPedia

Diagnostic List of Heating & Cooling Air Duct Defects: Things to Inspect, Check, Repair, or Replace

HVAC Supply & Return Air Duct Leaks & Obstructions - Theory vs Practice

Questions & Answers About Air Duct & Air Flow Problems on Heating & Air Conditioning Systems

Question: How do I Diagnose Too Little Cool Air Flow Downstairs?

Reply: Tips for diagnosing uneven air conditioning air flow between floors in a building

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

How to diagnose and fix an air conditioning system that is not working

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair