Heating & Air Conditioning Duct Routing & Support Guide InspectAPedia® -
Heating & Air Conditioning Duct Routing & Support Guide
Air Conditioning (or Heating) Duct Defects
Duct installation defects, safety hazards
Questions & Answers about proper HVAC duct routing and support
This HVAC duct design and repair article describes proper (and improper)
Heating & Air Conditioning Duct Routing & Support such as duct routing and support details to prevent or fix loose, sagging, crimped, bent or otherwise
defective heating or cooling ductwork. Crimped, squashed, or sagging ductwork restricts cooling or heating airflow into a building.
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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.
This chapter describes errors to avoid when installing ductwork in buildings. Avoiding these errors will result in improved
air flow, lower system operating cost, and may help in avoiding problems of mold or other contaminants in the heating or cooling duct system
of a building.
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 and repairs.
Ducts in ground contact
When heating and cooling ducts are placed in ground contact, such as in the crawl space shown in the photo,
not only is the contact going to conduct heat or cooling away from the duct before the air reaches its
destination, but further, there is a significant risk of water leaks/condensation in the duct in damp or flooding
areas (risking a mold
or health concern) or rodent entry.
Heating or cooling air ducts should be supported away from ground contact such as in crawl spaces.
Sharp Bends in Air Conditioning or Heating Duct Work Reduce Airflow
Sharp bends in ductwork restrict airflow (and violate ASHRAE or SMACNA guidelines for duct installations). Restrictions in
airflow through duct systems increase the heating or cooling system operating cost and reduce the comfort of building occupants.
This photograph
shows flex-duct in an attic making a too-tight 180 degree turn, crimping and restricting airflow in the duct system.
Excessive or Unnecessary Duct Lengths Increase Cooling or Heating Cost
Excessive length of ducts is often found where flex-duct is installed by an amateur. If you see a length of flex-duct
snaking across an area with multiple unnecessary twists and turns, the combination of length and unnecessary bends reduces
airflow, with the costs just cited above.
This photograph shows unnecessary lengths of small-diameter
flex duct left by the installer. The small diameter of these ducts also tells us that we're looking at a high-velocity
air conditioning system that uses a combination of small-diameter ducts and higher air velocity to deliver
cooling air to the conditioned space.
Flex duct runs should be as short and direct as possible without at the same
time causing inappropriately sharp bends or kinks.
Pinched or Crimped Air Ducts Reduce Heating or Cooling Airflow
Other common duct routing errors include sharp bends in duct work, mismatched sizes of duct work among sections,
flex duct which has become crimped or pinched to restrict air flow such as in the photo at left, and of course ducts which have become disconnected.
We discuss and illustrate disconnected heating or air conditioning duct defects at DUCT CONNECTIONS.
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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.
Air Diffusion Council, 1901 N. Roselle Road, Suite 800, Schaumburg, Illinois 60195, Tel: (847) 706-6750, Fax: (847) 706-6751 - info@flexibleduct.org - www.flexibleduct.org/ - "The ADC has produced the 4th Edition of the Flexible Duct Performance & Installation Standards (a 28-page manual) for use and reference by designers, architects, engineers, contractors, installers and users for evaluating, selecting, specifying and properly installing flexible duct in heating and air conditioning systems. Features covered in depth include: descriptions of typical styles, characteristics and requirements, testing, listing, reporting, certifying, packaging and product marking. Guidelines for proper installation are treated and illustrated in depth, featuring connections, splices and proper support methods for flexible duct. A single and uniform method of making end connections and splices is graphically presented for both non-metallic and metallic with plain ends." The printed manual is available in English only. Downloadable PDF is available in English and Spanish.
Owens Corning Duct Solutions - www.owenscorning.com/ductsolutions/ - provides current HVAC ductwork and duct insulating product descriptions and a dealer locator. Owens Corning Insulating Systems, LLC, One Owens Corning Parkway, Toledo, OH 43659 1-800-GET-PINK™
"Flexible Duct Media Fiberglas™ Insulation, Product Data Sheet", Owens Corning - see owenscorning.com/quietzone/pdfs/QZFlexible_DataSheet.pdf "Owens Corning Flexible Duct Media Insulation is a lightweight, flexible, resilient thermal and acoustical insulation made of
inorganic glass fibers bonded with a thermosetting resin."
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.
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.
"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]
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.).
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