Static Pressure Calculator

1. Clean filter in place, all registers and grilles open, blower on the speed it runs in normal operation.
2. Drill a test port in the supply plenum downstream of the coil, and one in the return plenum upstream of the blower.
3. Static pressure tip facing into the airflow, tubing to the manometer — supply to the positive port, return to the negative port.
4. Let it stabilize, then record both. Supply reads positive; return reads negative.
5. Seal the test ports when you're finished.

TESP = |supply static| + |return static| — a dual-port manometer totals it for you.

Always compare against the equipment's nameplate rated TESP. 0.50 in. w.c. is the common residential figure, but some units are rated at 0.30 or as high as 0.80 — the nameplate wins, and the blower performance table tells you what airflow that static actually buys you.

• Filter — loaded, wrong size, or too restrictive a media for the system.
• Indoor coil — dirty, or fins flattened and blocked.
• Registers and grilles — closed, blocked by furniture, or undersized.
• Ductwork — undersized, kinked or crushed flex, long uninsulated runs.
• Return — too few return grilles. This is the single most common cause of a high reading.

High static means low airflow, and low airflow shows up downstream as a freezing coil, low superheat and floodback risk, high blower amps, and a furnace tripping on high limit.

Under 0.30 in. w.c. with the blower at full speed usually means oversized ductwork, significant duct leakage, or the blower set to a tap higher than it should be. Airflow is high, which means poor dehumidification in cooling and too low a temperature rise in heating. It's less damaging than a high reading, but it's still a system that isn't delivering what the equipment was designed for.