Compare the actual airflow to the required airflow. Using a good quality commercial air balance hood, measure and record each supply register and return grille airflow. As soon as you get an air balance hood in your hands, you begin to understand what duct sizing and good installation is all about. Design is what you hope will happen after the system is built.
#HVAC DUCT SIZER VERIFICATION#
If you are an HVAC contractor or technician, email Doc for a free NCI duct sizing table that you can use in the field.ĭesign, without verification is cheap. If the duct is undersized and attached to an uncomfortable room, increase the duct size or add an additional duct along with the equipment replacement. Compare the required airflow to the listed airflow in the table as an indicator of an acceptable duct size. So here’s what you should do: Inspect the ducts and record their size. In other words, we see lots of really low airflow. From this data we have also learned that the typical system is operating at pressures more than 50% higher than the system fan ratings. We have listed duct types and sizes and published actual measured delivered airflow that you can use to check existing duct sizes in the field.īottom line, ducts deliver far less airflow than what you think.
Using this data, NCI has created duct sizing tables that realistically indicate typical airflows.
#HVAC DUCT SIZER SOFTWARE#
National Comfort Institute (NCI) has a software tool called ComfortMaxx for HVAC professionals to use to measure, record, and diagnose the performance of HVAC systems all over the country, every day.īecause we have access to this data, we can "see" duct system performance like never before. If there are return air filter grilles, the pressure of the filters must be excluded from the return duct pressure. If the system has an external cooling coil, the supply or return duct system pressure is only allowed 25% of the maximum-rated fan pressure each. Compare them to 50% of the maximum rated fan pressure at the specified system airflow. Step Three - Read and record supply and then return duct pressure.
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