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Certified Air Balancing

What is Air Balancing? Air balancing the process of adjusting an HVAC system to perform as designed, and the recording of applicable measurements, adjustments, etc. Mechanical engineers and architects design HVAC systems to provide a certain amount of air to each diffuser or air outlet. In general, an air balancer adjusts the equipment, dampers in the duct work, and diffuser dampers so that the systems being adjusted meet the specifications of the building plan. When we are hired to perform air balance reports for other mechanical contractors, we use the company "Thermal Flow" to avoid confusion. Work done for architects, engineers, and building owners may be done under the company name "Johnson Heating and Cooling, LLC" depending on political considerations. Which ever company name we use on the report, it is the individuals at Johnson Heating and Cooling, LLC who do the work, and our customers can rest assured that we can be trusted to look out for their best interests when we deal with their customers.

Air balancing became a popular requirement of local mechanical inspectors in the State of Michigan in 2006. Before 2006 most mechanical inspectors in the State of Michigan did not require certified air balance reports for small and mid-sized commercial and industrial structures. A certified air balance report ensures that the owner of the structure gets what he has paid for, in that it verifies that the HVAC systems in the structure are tuned to function as intended in the original designs.

Air balancing may be subdivided into three parts, and those parts are equipment adjustment, damper adjustment, and documentation. Each part is equally important and usually equally necessary for a successful air balance report. Most systems that require air balance reports, or systems that are for commercial and industrial structures have lower fans that are driven by a belt and pulley. For systems that have direct drive blower assemblies, equipment adjustment may still be necessary, however often times no adjustments need to be made.

The amount of air moved by a belt and pulley system can be adjusted by increasing the diameter of the pulleys on a belt and pulley drive system. Conventional electric motors (alternating current motors) tend to maintain an RPM very close to that listed on the motor name plate, which is based on the frequency of the electricity that powers the motor (in the USA, 60 hertz). Small variations of +/- 2% may be present in typical systems, if the load is much higher or much lower than the manufacturer has anticipated, however, for all practical purposes, air balancers all but ignore variations in the blower motor speed, as they are generally considered a constant variable. Because the speed of the blower motor is relatively consistent to what the motors RPM rating is, the pulley on the motor may be increased or decreased in diameter to achieve a faster or slower RPM on the blower pulley (respectively). For an air balancer, one of the most important tasks to achieve adequate air flow through an HVAC system is adjusting the pulley on the blower drive system. The larger the diameter on the blower motor pulley, the more air is moved. When adjusting the pulley on a blower motor, an experienced air balancer is always mindful of the amp draw of the blower motor. If the blower motor is drawing too many amps, the motor windings may be destroyed. The FLA or full load amps rating on a motor indicates the amount of amps that a motor may draw without being damaged due to too much current. There may also be a listing called SF or service factor on the motor name plate. The service factor of a motor is a number that may be added to the FLA to determine the absolute maximum manufacture's "do not exceed" amp draw rating for a motor. The service factor value is an allowable "margin" or "safety factor" that the motor manufacture includes to account for times when the load on a motor may be temporarily increased, for example; when a panel is removed the blower moves more air and the load on the blower motor goes up.


  1. Another point of interest in regards to equipment adjustment is the amount of out door air being brought into a structure. The State of Michigan Mechanical Code requires a certain amount of out door air be brought into nearly every commercial and industrial structure. The requirement to bring out door air into a structure is for the safety of the building occupants and varies based on factors like: structure classification, occupancy load, and ventilation requirements based on the needs of other equipment (i.e. exhaust fans, etc). The means of any mechanical system to provide the structure with adequate out door air vary by system design, but most often include an air damper that allows a certain amount of fresh air to enter the air steam of the HVAC equipment via the return or negative pressure side of the blower motor. A system that brings in too much outdoor air will be inefficient, and a system that brings in too little out door air will endanger the occupants of the structure. The amount of out door air intake of HVAC systems should be very important to the building owner, and is almost always a major point of interest to mechanical inspectors.



The second part of air balancing is damper adjustment. Damper adjustment is pretty strait forward. If an air terminal is providing too much air flow, then it's damper needs to be closed. If a certain air terminal is providing too little air flow than the damper for that air terminal needs to be opened, or, the other dampers for the other air terminals need to be closed. Adjustment of air dampers is easy work, however, a skilled air balancer, with years of experience, is much better at anticipating how the system pressures will change with every damper adjustment, allowing him to complete his work in a fraction of the time needed for a less experienced air balancer to do the same. Air balancing is a skill as much as it is a science.

The third part of air balancing is the documentation. Johnson Heating and Cooling, LLC prides itself on being technologically advanced. Our efficiencies in computer related tasks allow us to provide our customers with excellent services at competitive pricing with unmatched quality. The only thing that we use a pen or pencil for in our final reports is for signing our names on the report when it is finished. We provide our customers with paper and electronic copies of our reports, which cuts down on administrative costs. We print the reports on-site to save time and lower job costs. We are extremely organized and mechanical inspectors love our work. In the Air balancing industry the use of computers is often undervalued. We use program templates for our jobs and our customers save money. Furthermore, a typed report is always better received than a hand written report. If a system can balance, we get the job done, and if it is incapable of balancing we are tactful in our reporting and always try to protect the interests of those who hire us. Because we have a State of Michigan Licensed Professional Engineer on staff, our conclusions carry weight, when they might otherwise be disputed. David Johnson Sr., the father of Johnson Heating and Cooling, LLC's owner, David Johnson Jr. is one of the less than 200 mechanical inspectors in the State of Michigan, so when we need to deal with a mechanical inspector on a customer's behalf, we are in familiar territory. Honesty, quality, experience, and competitive pricing makes Johnson Heating and Cooling, LLC an excellent choice for doing your air balancing work!