Measure the static pressure in the supply and return plenums while the blower runs. Added together, they give total external static pressure, which should land between 0.30 and 0.50 in. w.c.
Pressure units
Reading in the supply plenum, just after the coil (usually positive)
in. w.c.
Reading in the return, just before the blower or filter (usually negative; the sign is ignored)
in. w.c.
–
00.300.500.751.00
LowTarget rangeHigh
Enter both pressures
Your result appears here as soon as you fill in both readings.
Common things to check
For best accuracy, take both readings with the filter in place, the blower at its normal cooling speed, and all registers and doors in their usual positions. Use a digital manometer and test ports in the plenums. Check the equipment nameplate too, since the rated static pressure varies by unit. This tool is a quick screening aid, not a diagnosis; have a qualified HVAC technician confirm any problem.
