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This article describes the proper location and placement of air supply and air return registers in HVAC systems and addresses problems such as misplaced or missing air conditioning cool air supply or return air registers, improper cooling duct routing, cooling (or heating) air duct corrosion, and defective heating or cooling duct work. This article is part of our series How to Inspect, Diagnose, & Repair the Air Conditioners or Heat Pumps.
LOCATION OF REGISTERS & DUCTS - Location of air conditioning return or supply outlets
Supply and return too close together
You don't have to be
an HVAC design engineer to see that in the photograph at page top and shown again here the air conditioning supply register is above and just
a few feet from the central air conditioning return grille. Cool air delivered to this attic room
will mostly fall down to be simply drawn right back into the return.
Poor supply and return duct
locations like this can severely reduce the effectiveness of the cooling system and increase its
In this particular home the installer was confronted with a shoehorn retrofit
of the air handler and duct work into a sub-standard attic bedroom closet in an area where s/he
was not permitted to open cathedral ceilings nor to construct a delivery duct along the ceiling or
under the floors. It was a costly to operate and poor performing air conditioning installation.
Location of Heating or Cooling Return Registers in Basements
The photograph shows a basement door into which an installer cut two return air inlets to feed basement air
back to an air return located at the basement air handler.
As we discussed at INCREASING RETURN AIR,
this is a poor design that increases heating or cooling system operating costs.
In addition to that issue, placement of return air inlets in basements, depending on their location, risk other potential hazards including:
Carbon monoxide hazards: Return air registers too close to oil or gas fired equipment may draw combustion gases or carbon monoxide into the
air duct system, sending dangerous gases into the living space
Carbon monoxide production may be increased and heating fuel combustion incomplete at nearby heaters, water heaters, or even gas clothes dryers, if
the air handler is pulling return air from a confined space where combustion equipment is also located.
Air-starved equipment may not
only work improperly, but may be unsafe, producing dangerous carbon monoxide. We've also found this problem in basements where the
owner, attempting to improve basement air quality, ran powerful exhaust fans continuously.
Placement of Heating or Cooling Air Returns at Outside Walls
Heating or cooling return air duct systems which place the return register at outside building walls
may perform poorly.
heating authorities opine that more effective and economical design places
these registers on the interior walls - the outside walls and perimeter of
some rooms may be chilly even when the heat is operating.
Other Bad Locations for Air Registers
Our photo (left) shows an octopus furnace located in the basement of a pre-1900 home. All of the return air to this system is drawn from the un-heated basement floor - a "one-way" air movement heating design that increases heating costs as well as risking pick-up of dust, debris, or anything else undesirable from the basement area.
At UNSAFE DUCT OPENINGS we describe other air register location mistakes that can be dangerous, such as cutting a return air opening near heating equipment or in hazardous areas like a wet moldy crawl space.
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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 - firstname.lastname@example.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."
"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]
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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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 Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.