Is it acceptable to install an "A" coil in the return air plenum of a furnace?

Installing an "A" coil in the return air plenum of a furnace can be an acceptable practice under certain conditions, specifically when it pertains to heat pump systems that are retrofitted onto existing electric forced air furnaces. In these scenarios, the "A" coil is designed to handle the cooling aspects of the heat pump effectively, ensuring that the refrigerant can circulate properly and providing efficient cooling performance.

In this configuration, the design of the "A" coil allows it to be positioned within the air plenum to facilitate the necessary airflow and heat exchange processes. This allows the system to operate effectively, providing both heating and cooling as required. The key consideration is that the installation aligns with local codes and best practices, ensuring safety and efficiency in the overall heating and cooling system. Proper installation is crucial because it must ensure that there is no obstruction to airflow and that the system can operate without causing pressure imbalances in the ductwork.

This scenario contrasts with options suggesting that installation is generally impermissible or highly discouraged, which overlooks the specific context in which adding an "A" coil can be beneficial and acceptable. Thus, when done thoughtfully, this practice can enhance the functionality of a heat pump system in conjunction with an existing furnace.