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• Heating & Air Conditioning Air Flow Balancing Advice
• Air Conditioning (or Heating) Duct Defects

This chapter of "How to Inspect the Central Air Conditioning or Cooling System" describes proper (and improper) balancing of heating & air Conditioning duct air flow in residential buildings and in commercial office space includin high-rise buildings. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links 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.

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 occuped 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.

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