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BENJAMIN DIMARCO, LEED AP If your technicians aren't checking system airflow on every service call, you're doing your company and your customers a disservice. Air balancing is the missing link in getting residential HVAC systems to perform at or near their peak levels. In the commercial, industrial, and institutional markets, HVAC balancing is more recognized and accepted as a necessary service than it is in the residential market. We have found, however, that the need for residential air balancing may be even greater than in the other markets simply because of the lack of awareness that has existed for so long. The residential projects on which we have provided these services have turned out to be exceptional in terms of overall system performance. Not all residential customers are ready for their HVAC system to be balanced, but you can be assured that just about all residential customers need it. Testing is the Key The key to proper residential air balancing is testing. If you don’t measure, you’re just guessing. After testing more than a thousand HVAC systems we have found less than 5% that are operating above 90% of the equipment-rated capacity. Most operate in the 55% to 65% range before balancing or corrective measures are put in place. Our existing clients have been apprised of the need for air diagnostics and balancing and many of them have gone through the process to test, assess, correct, and verify their system’s performance. Any new clients we take on are informed immediately that airflow diagnostics, balancing, and full system commissioning are necessary unless they have already had it done. If they are not prepared to proceed, we are honest with them and tell them that traditional service and maintenance can be done, but overall system effectiveness and performance is not guaranteed. The Process There is a distinct process to balancing a residential HVAC system. You first assess and measure or "test-in," then re-assess, perform any corrective actions, "test-out," verify, and document. Here is how to put that process into motion on a project. You need to test-in to get a baseline. If a 3-ton system is supposed to deliver 1,200 cfm and you measure the duct system and find that the supply is delivering 1,000 cfm and the return is returning 800 cfm, there is obviously a problem. Our experience has shown that nearly all duct systems are deficient to some level, the return system usually much more so than the supply. We usually find duct leakage on both sides of the system and an inadequately sized return system. Airflow can be measured several ways. One of the simplest ways is to test total external static pressure, compare it to manufacturer's documents, then measure airflow at all the supply and return grilles and registers. Next, assess how much air is moving through the furnace or air handler and how much is being delivered to and returned from the living space. From this test-in procedure you can assess the deficiency level, and make the appropriate recommendations to the homeowner for repairs. These recommendations may include duct sealing, adding return ducts and grilles, modifying or changing the filtration set-up, adjusting fan speeds, cleaning the evaporator, performing combustion analysis, and adjusting the refrigerant charge. After this work is complete, test-out and document the results showing the measured improvements in performance. This is when you perform the final balancing, setting and adjusting dampers, etc. to achieve the desired end result. Overcoming Challenges Most of the time, customers want the necessary duct system repairs done without disruption to finished walls or ceilings. Homes with finished basements where the ceiling is drywall rather than a drop ceiling make duct sealing and repairs very difficult. In these cases the customer must weigh the projected HVAC improvements with the cosmetic disruption and repair required to achieve them. We find that customers are usually receptive to minor disruption such as cutting some access openings into a basement drywall ceiling, but not major disruption such as cutting entire wall spaces open on the first or second floors. Another obstacle is running additional ducts to a second floor from a system located in a basement. Unless we can route the ducts through a closet or hidden chase, this is usually not done. When we only have to add additional returns, we typically locate the grille on the first floor near the foyer and near the stairwell to the second floor. This allows a central supplemental return that can draw air from both floors. Learn to Use the Tools Keep in mind that building envelope issues can add to the airflow and HVAC system problems in a home. Air balancing will assist in improving the performance of the HVAC system, but may not cure all the comfort problems that exist within the home. A full building analysis that focuses on the building envelope may be necessary. Air balancing residential HVAC systems really is the key to achieving maximum performance and optimum comfort. It is a simple matter for service technicians to perform an airflow calculation and begin to educate customers on the importance of a properly balanced system that is delivering the correct amount of airflow. Learn how to use airflow measurement tools, and then use them! Test-in, test-out and verify system performance. Remember: if you don’t measure, you’re just guessing. And guessing isn’t good for your customers or your company. Benjamin M. DiMarco, LEED AP, president of DiMarco & Associates LLC, Chagrin Falls, OH, is certified by the National Comfort Institute, which provides training, equipment, and support for HVAC contractors performing air diagnostics, balancing, combustion analysis, and carbon monoxide detection. He can be reached at  (440) 647-8876  , or by e-mail at ben@dimarco-associates.com. For more information about the National Comfort Institute, visit www.nationalcomfortinstitute.com.