In a ducted system with a cooling coil installed and an existing furnace heat exchanger, where must the air first flow through according to code?

In a ducted system where both a cooling coil and a furnace heat exchanger are present, the code typically mandates that the air must first flow through the heat exchanger before passing through the cooling coil. This is primarily to ensure that the heating function of the furnace can effectively warm the air before it is either cooled or circulated throughout the space.

The design intent is to maximize the efficiency of both systems. By allowing the air to first be heated in the heat exchanger, it helps to prevent the cooling coil from having to work harder to reach the desired temperature. This sequence also includes safety considerations, as it ensures that any potential condensation or moisture that might occur in the cooling coil does not adversely affect the heating system. Proper airflow is essential for both heating and cooling operations to maintain efficient temperature control and energy use within the system.

Adhering to this airflow sequence also ensures compliance with safety and performance standards as dictated by the relevant building codes.