Where should the probes be placed to take an external static pressure reading in relation to a furnace?

The correct placement for taking external static pressure readings involves positioning the probes between the furnace and the filter, as well as between the furnace and the evaporator coil. This method is essential for accurately assessing the airflow and pressure conditions affecting the furnace's performance.

When gauges are placed between the furnace and the filter, it helps technicians evaluate the pressure drop caused by the air filter. A clogged filter can significantly restrict airflow, leading to improper furnace operation and potential overheating.

Similarly, taking a reading between the furnace and the evaporator coil allows for the assessment of pressure changes due to the evaporator's influence on the heating system. It is crucial for understanding how the cooling system may affect the overall airflow when the air conditioning is running.

In summary, placing the probes in these specific locations provides comprehensive data about the static pressure in the system, which is fundamental for diagnosing issues related to airflow, efficiency, and overall system health. Proper measurements help ensure safe and effective operation of the HVAC system.