Airflow Measurement Tests

To be eligible for duct sealing in the program, the duct systems must meet the following airflow rates for the equipment they serve.

  • For systems with cooling, CFM per ton must be at or above 200.
  • For fossil, fuel/Electric Furnace only heating systems, the measured Heat Rise must be within the manufacturer’s recommended range. Program default maximum temperature rises 80 deg F. will be used when manufacture data is not available.

NOTE: When finishing the Flow test on cooling equipment, set the thermostat on cooling mode for the most precise airflow results. When outside temperatures are less than 60 deg. F., don’t turn the cooling equipment should on, use the fan-only mode.

  • Duct systems with accessible filter slots at the air handler or accessible single return filter grille will use True Flow Plates to measure system airflow. Refer to the TrueFlow® Air Handler Flow Meter Operation Manual for installing the True Flow Plates and correctly measuring system airflow.

NOTE: When you can’t get the model number for the cooling equipment to know the required system airflow eligibility, use the following as a default

  • 300 cfm per 500 sq. ft of conditioned cooling space.

Heating only systems will use the Temperature Rise method to measure system airflow. This method is defined here:

  1. Drill a ¼ inch hole in a straight section of the supply plenum or trunk. Be sure the hole is around at least one duct bend. The temperature probe should not have a direct “line of sight” with the heat exchanger.
  2. Drill a ¼ inch hole in a straight section of the return plenum or trunk.
  3. Insert a temperature probe into each drill hole in the Return and Supply. Be sure the probe extends into the middle of the duct and not along the sides. 
  4. Turn the system on and allow it to run for 10 minutes or until the supply and return side temperatures stabilize.
  5. Read and record the supply and return side temperatures. Subtract the return side temperature from the supply side temperature. This is the systems’ temperature heat rise.
  6. Compare the measured heat rise from steps a-e to the manufacturer’s acceptable heat rise range for the system data plate (red box)
  7. If the measured heat rise falls within the manufacturer’s projected range the airflow is acceptable and the system can be sealed.

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