Why is there a filter in the mixed air plenum before the fan of a duct heating system?

Having a filter in the mixed air plenum before the fan of a duct heating system is crucial for ensuring that fan efficiency is not compromised due to debris and contaminants. As air flows through the system, it can carry dust, pollen, and other particulates that may accumulate on the fan blades over time. If these particles build up, they can create an imbalance in the fan's operation, leading to reduced airflow efficiency and potential overheating or mechanical failure.

By installing a filter at this point in the system, these unwanted contaminants are caught before they can reach the fan. This not only promotes optimal performance but also extends the lifespan of the fan and reduces maintenance needs. The result is a more reliable heating system that operates at peak efficiency, ensuring adequate heating and airflow while minimizing energy consumption.