What does the airflow measurement decide?

The measured airflow is compared with the airflow the selected equipment requires from the manufacturer's data. If the ducts deliver it at acceptable static pressure, the system is acceptable as it stands. If not, the outcomes are to modify the ducts, replace them, or select equipment the ducts can support.

The same number sets a ceiling. Generally speaking, measured airflow divided by about 400 cubic feet per minute per ton is the largest heat pump or air conditioner the existing duct system can carry; a heat pump replacing a furnace needs more air for the same heat, so this ceiling is checked before a heat pump is selected. The load calculation and altitude derate supply the demand side of that comparison; the airflow test supplies the delivery side.

The static-pressure profile taken with the test locates the restriction when the number falls short: filter, coil, return, or duct run. Return-side restrictions are the most common and usually the least invasive to correct.

Last reviewed 2026-09-06. Accurate to the best of our knowledge as of that date. Rules change — that's why the date is there.