HVAC Procedure and Performance Guide

Measure air-flow at register

Training for this procedure can be found in these courses:

                         131 – Oil Heat l  and  161 – Boilers l


Register air-flow must be determined using register manufacturer’s specifications for measurement and recommended equipment.


  1. Review register manufacturer’s specifications.
  2. Determine instrument and type of probe required, register flow factor and register effective area.
  3. Collect tools, equipment and materials needed.
  4. Put on safety and protective equipment and apparel.
  5. Verify that system is operating, that dampers are open and that filters are clean.
  6. Take velocity measurements according to manufacturer’s instructions.
  7. Calculate register air-flow using manufacturer’s specified method. (Note:  Air-flow hood may be used for direct CFM reading in lieu of measurements and calculations in Step 5).
  8. Document calculations and register location.
  9. Leave equipment in required operating status.
  10. Remove safety and protective equipment and apparel.
  11. Gather tools, equipment and leftover materials, and leave work site clean.