Total External Static Pressure (TESP) is the resistance the blower fan has to overcome to push air through the entire duct system — including the filter, evaporator coil, supply ducts, registers, and returns. Measured in inches of water column (in. WC), it's the HVAC equivalent of blood pressure.
Most residential air handler blowers are rated for TESP between 0.5 and 0.8 in. WC. Higher TESP means the blower has to work harder, draws more electricity, moves less air, and wears out sooner.
Common causes of high TESP in Charleston homes: too-restrictive filter for the system (e.g., MERV 13 in a 1-inch cabinet), undersized return ducts, closed supply registers, dirty coil, or kinked flex duct.
Any quality HVAC tech can measure TESP with a digital manometer in 5 minutes. If your TESP has never been measured, ask for it on the next service call — it's the single most diagnostic number on a residential system.
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