Air Balancing as a Verification Tool

Dec. 21, 2011
Testing and balancing has been the specified method of verification of commercial HVAC system performance for over 50 years.

Testing and balancing has been the specified method of verification of commercial HVAC system performance for over 50 years. Only now is it beginning to be utilized in residential system verification. Let's take a look how this timeless art is moving into its rightful position as the preferred verification method in the residential HVAC industry.

Manufacturer’s Specifications

When equipment is designed and manufactured, it’s then tested and its highest potential capacity and efficiency are carefully verified and documented under perfect conditions in laboratory. Specifications are then published detailing the maximum capacity in the equipment’s engineering specifications.

Air balancing is the prescribed method to measure the performance of that equipment once it has been installed into a building, coupled with other components, hooked to a flue, and a gas and electrical system. The equipment is then connected with a line set and stuck between a supply and return duct system. For residential systems, the contractor is often handed a set of plans on a house without a mechanical plan and told to find the lowest cost way to install the system.

The air balancer's job is then to measure the live operating performance of the system and to publish a report comparing his or her field collected data to the manufacturer’s specifications and the requirements of the designer.

Required Inspections, Tests and Calculations

The balancers job includes inspections, testing and calculations that quantify the level of performance achieved by the installation. Tasks include verifying the right equipment was installed by inventorying the equipment specified by the designer and assuring that it was installed to meet the designers and manufacturer’s specifications.

Measuring its performance is the ultimate verification. This series of tests jump right to the bottom line. The question “does the system work as it was intended to?” is answered by the balancing report. The only way performance can be achieved is to measure its operation live in the field. If the performance is there, all the subordinate criteria have been successfully met and the results have been delivered. Results are verified by comparing each measurement and calculation to the manufacturers and designers specifications.

The holistic view of live field measurement and calculated actual performance is so superior to the splintered tests currently being used that there’s little question that performance verification by air balancing trumps every other HVAC verification method available today.

Tests included in air balancing are fan airflow, delivered airflow at the grilles, and a live supply and return duct leakage number. Total external static pressure and the pressure drop of each major system component, including the actual operation of the duct system is taken and compared to manufacturer’s and industry specifications.

Wet bulb and dry bulb temperature are measured near the equipment and throughout the system. When combined with airflow readings Btu capacities of the equipment can be accurately calculated and compared to equipment capacities as published by the manufacturer and are adjusted for actual operating conditions at the time of the testing. System losses and gains can also be calculated and documented.

Live electrical measurements are taken, recorded and compared to specifications. Fan horsepower and RPM are verified by voltage and amperage readings. It’s amazing what can be verified when the system is measured under live operating conditions.


Fan pressures, coil pressure drop, and filter pressure drop are compared to manufacturer’s specifications. Live pressure measurements throughout the duct system also check for adequate duct sizing and the effectiveness of the duct installation. System defects can be identified by measuring fitting pressure drops. Fan law two can also be used to calculate how each pressure drop can change as airflow is changed to match the required or specified airflow.


Air balancing verifies that the manufacturers required airflow been delivered. It also provides evidence that the equipment generated BTU is to be moved from the equipment into the building and that the duct system is not losing airflow on the supply side or pulling unconditioned air into the system from the return side. This will offset the BTU generated by the equipment functions.

Airflow can be specified by load calculations intended to satisfy the heat loss or heat gain of a room, but unless required airflow is measured there is no evidence that this requirement has been met for each individual room.

Evidence that current verification methods miss the mark is revealed by the fact that the effects comfort system efficiency has never been studied adequately by the energy efficiency community.

As each manufacturer designs and builds HVAC equipment, and it passes through the rigors of AHRI and government required testing, specifications are published from which marketing materials are created that consumers use to make purchase decisions. Unfortunately these specifications created under ideal laboratory conditions have been utilized to determine incentives paid from rate payer funds without verification that the installed systems are delivering what was specified. Manufacturer’s specifications only express the potential of this equipment under ideal operating conditions. Without verification of live operating conditions as offered by air balancing, the results of equipment replacement are unknown.

With the advances of air balancing over the past decades using advanced calculation software, live annualized efficiency numbers can now be created and published for the benefit of the consumers. Forward thinking utilities are now taking advantage of this breakthrough and are moving ahead of the verification methods of the past.

Top notch contractors and energy professionals are able to deliver far superior verification methods in the open market outside of utility programs to gain a significant advantage over their competitors using these test methods to prove delivered results compared to the lower class of contractors that quote equipment efficiencies as their delivered result but fail to prove it to consumers.

Rob “Doc” Falke serves the industry as president of National Comfort Institute an HVAC based training company with technical and business level membership organizations. If you're an HVAC contractor or technician interested in air balance test procedures, contact Doc at [email protected] or call him at 800-633-7058. Go to NCI’s website at for free information, articles and downloads.

About the Author

Rob 'Doc' Falke | President

Rob “Doc” Falke serves the industry as president of National Comfort Institute an HVAC-based training company and membership organization. If you're an HVAC contractor or technician  interested in a building pressure measurement procedure, contact Doc at [email protected]  or call him at 800-633-7058. Go to NCI’s website at for free information, articles and downloads.