External Supply Pressure Measurement is Critical

For measuring external supply pressure in a furnace, the recommended ranges and best practices are:

Recommended High and Low Range Readings

1. Low Range: Typically, the static pressure on the return side should be between 0.1″ to 0.3″ WC (inches of water column) depending on the system design and components13.
2. High Range: The supply side pressure is often higher, ranging from 0.3″ to 0.8″ WC, with variations based on ductwork, filters, and evaporator coil conditions14.

Best Measurement

• The Total External Static Pressure (TESP) combines both return and supply measurements. Most furnaces are designed to operate at a maximum TESP of 0.5″ WC, but this can vary by manufacturer24.
• To ensure optimal performance, compare the measured TESP to the maximum rating specified on the furnace’s nameplate or in its manual. If the TESP exceeds this value, airflow restrictions may exist, requiring adjustments or repairs