Three Methods for Checking Airflow on Service Calls
We are all in the business of moving heat, and in order to move heat, you need to move air. In far too many cases, residential HVAC units are oversized and ductwork is undersized, resulting in poor air distribution. Improper airflow negatively affects suction and discharge pressure, superheat, sub-cooling and proper temperature rise across heating coils, which can to heat exchanger failure. Always check airflow on service calls and take necessary corrective actions.
Here are several ways to measure airflow:
Static pressure
Testing total external static pressure (TESP) is usually done using a digital manometer or magnehelic. Compare measurements to the manufacturer’s blower performance chart; most are easily accessible online. The higher the static pressure, the lower the volume air.
Measure CFM
Use an airflow hood or anemometer to measure CFM. Start with the return, because if the system is not pulling enough air at the return, airflow will be restricted at the supply side as well,
Calculate airflow
A simple mathematical formula can be used to calculate airflow. Place the furnace in heating mode, then divide the total output BTUs listed on the nameplate by 1.08. Multiply the result by the temperature difference between the return and the supply; this is your CFM.
To measure CFM on a heat pump with an electric strip heater, turn the strip heater on. Measure voltage and amperage, then multiply them by each other. Multiply that result by 3.413 to find BTUs, then divide BTUs by 1.08 to find your CFM.
About E.P. Homiek
E.P. Homiek Sheet Metal Fabrication & HVAC Supply, with two convenient locations in Lakewood, NJ and Union, NJ, provides one- to two-day turnaround on all residential and light commercial ductwork, as well as one- to two-hour emergency fabrication service, rapid delivery, and competitive prices. HVAC parts, supplies, and equipment lines include Goodman, Honeywell, Bryant, Bradford White, Crown Boiler, Daikin, Weil-McLain, Sea Breeze, Generac, Fantech, ZM, A.O. Smith, Hart & Cooley, Malco, Mueller, and many more.
