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Air Balancing ABCs

What is air balancing anyway?  It’s a vital part of a 3-part process of testing, adjusting and balancing your HVAC system to deliver the right amount of air to each room of the building.  The actual air balancing process includes a number of related tests that determine the performance of your heating and air conditioning system.


What is Commercial HVAC Air Balancing?: delivering the proper cubic feet per minute (cfm) of air that each room needs to receive, based on its size and conditions.

Why Building Owners & Property Managers Should Care?: More is not necessarily better when it comes to room air delivery. Rather, getting the optimum amount of air delivered to each room prevents hot and cold areas within your house, affects how much you pay in utility bills each month, and can even affect how long some components last.

Factors that affect air balancing: size of the room; size, type and condition of the ducts; fireplaces and chimneys; kitchen exhaust fans; bathroom vent fans, etc.

Who Performs Commercial HVAC Air Balancing Services?:  HVAC contractors who install or repair AC and heating systems should include measured, optimum air balancing as part of their work. There are national organizations that provide training and certification for HVAC contractors specifically focusing on air balancing.

When Should Air Balancing Services be Performed?: As part of the final installation stage for a new HVAC and ductwork. For existing systems, it would be done with an energy audit, duct sealing or replacement, or when replacing major components.

Rooms that are consistently too hot or too cold is a typical symptom of an HVAC system that may need balanced. If your ductwork has design deficiencies, they will probably need to be corrected before your system can be balanced.  Once the ductwork is corrected…in order to properly balance the delivery of conditioned air, your HVAC contractor first needs to calculate the airflow requirements for each room and adjust the airflow accordingly. Your contractor may need to install adjustable balancing dampers.

Causes of Un-Balanced or Poor Air Flow Through Commercial Building HVAC Systems

Here are several major issues to consider as possible causes of inadequate cool or warm air delivery to some building areas:

  1. Location of Air Supply and Air Return Registers Causing Un-Balanced or Poor HVAC Air Flow
  2. Single Return Air Inlet & Un-Balanced Cooling or Heating Airflow
  3. Poor Heating or Cooling Air Flow & Debris & Contaminants in Ceilings Used as Return Plenums Risk Entrainment in Building HVAC Airflow
  4. Openings that Subvert Proper HVAC Duct Airflow – a) Missing or incomplete ceiling partitioning, or   b) Open windows
  5. HVAC Duct layout problems: Un-balanced HVAC air flow or cool air or warm air delivery due to differences in HVAC duct length, diameter, bends, restrictions may fail to properly balance air flow across a long flat building, between building floors, or where ducts have to make torturous passage from one building area to another
  6. Vertical air flow problems: in a tall building, even a residential property, if a single air handler is used for both heating and cooling, a basement located air handler will have an easier time pushing warm air up into higher floors of the home than it will pushing cool air up into the same spaces during the cooling season.
    (Warm air rises through a building by convection while heavier cool air tends to fall). Increased fan speed for cooling operation or booster fans may help. To avoid this problem some HVAC designs use two air handlers, placing the second unit in the attic or ceiling above the uppermost floor.
  7. HVAC Duct leaks: leaky ducts or even open duct connections, especially undiscovered in hidden areas, can completely subvert balanced cool or warm air flow distribution in a building even if the original duct layout and design were well done.
  8. Stuck or not-working HVAC Duct Dampes, Booster Fans: check to make sure that duct balancing dampers have not been manually left in the wrong position (shut, open when should be partly closed, etc) and that automatic devices such as duct balancing dampers and duct booster fans and their controls are in fact operating
  9. Inadequate return air or tight rooms: if a building uses centralized return air inlets to the HVAC system then remote building areas may lack adequate air flow because of inadequate return air flow out of that building area back to the system air handler; for example closing the door to a room that has no in-room return duct inlets may substantially reduce the flow of conditioned air into that room.

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