Guide to Balancing Heating & Air Conditioning Air Flow in buildings InspectAPedia® -
Heating & Air Conditioning Air Flow Balancing Advice
Questions & Answers about balancing air delivery or air supply in duct systems for heating and air conditioning
Air Conditioning (or Heating) Duct Defects
This HVAC ductwork diagnosis and repair article describes proper (and improper)
balancing of heating & air Conditioning duct air flow in residential buildings and
in commercial office space including high-rise buildings.
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Balancing Air Ducts for Proper Warm or Cool Air Delivery
Look for indications that the system has not been balanced for optimum air flow:
Uneven temperatures throughout the air conditioned space, room to room, or within rooms, when the system is operating
All registers are open but airflow varies widely from register to register
You may want your service person to review air flow in different rooms, to add manual balancing dampers in the duct system (and show
you where they are located and mark on the duct just where the balancing damper levers are normally set.
Air conditioning cool air balancing in offices & commercial spaces
Location of Air Supply and Air Return Registers in Commercial buildings
The photographs above show both supply and return ceiling registers in a commercial office space. In this case they are located too close
together. The second photograph shows that a ceiling tile has been removed from a suspended ceiling over an office which uses
the ceiling cavity as a common return air plenum. While this may produce more airflow in the office where this suspended
ceiling tile was removed, it has unbalanced the entire air conditioning system for the rest of the offices in the building.
Many commercial spaces and offices are cooled (and sometimes heated as well) by an air handler which delivers
supply air to each office area by flex duct connected to ceiling registers.
Return air is passed back to the
air handler through the large common space above a suspended ceiling over the occupied space. Special vents either
around the supply registers or placed separately are intended to pass return air to the common ceiling space,
and their location and adjustment are important to provide balanced airflow in the work space.
Debris & Contaminants in Ceilings
This photograph shows a common ceiling plenum over a commercial office space in a Manhattan high rise building. Notice the considerable amount
of debris atop the ceiling tiles?
All of the office conditioned air moves through this area, risking additional levels of irritating or harmful
particles, particularly if the debris contains asbestos fragments or lead paint chips. (In this particular case tests showed that this was not the case.)
Here are
some common concerns or defects in commercial installations that use this design:
Missing ceiling tiles: People in individual offices subvert the system by seeking more or less cool air by removing suspended ceiling tiles. These
un-planned openings make it impossible for the system to be properly balanced.
Common return air plenum Use of the ceiling space as a giant return plenum above the work area means that any debris, mold (perhaps
from roof leaks), fiberglass, asbestos, or other problematic particles that are in this space are readily circulated through the building air
These photos show a common ceiling return air plenum over commercial offices. In the first or left hand photo, notice that
rectangular opening in the distance? The second photo is a closeup. Openings had been left open between the office space and
the top floor hallway and also between the hallway and other office spaces in the building, so that particles, leak-related mold, or other
irritating particles developing over any office will be shared among all of the tenants on this building floor.
Missing or incomplete ceiling partitioning in large commercial buildings may mix air (and odors or contaminants)
from multiple offices or building use areas, redistributing these un-wanted odors or particles to other building areas. One of
our clients who maintained a law office in a strip mall complained of chemical odors which were traced to a beauty parlor
located at the extreme other end of the building.
Open windows, especially in a tall office building such as shown by this photograph, cause a tremendous up-draft
through the building, moving particles, gases, or other potential IAQ concerns up through the building.
In this instance the
office occupants on the 18th floor of this Manhattan office opened their windows and also their office entry door to
try to cool off their offices because they were unable to turn off the building heating radiators.
Questions & Answers regarding this article
Questions & Answers about balancing air delivery or air supply in duct systems for heating and air conditioning
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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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