When a split system air conditioner has a counterflow air handler, what are the best locations for return air grilles?

In a split system air conditioner with a counterflow air handler, the best locations for return air grilles are ideally positioned on a sidewall next to the ceiling. This arrangement is beneficial because warm air tends to rise, and placing the return grilles higher allows for the efficient removal of that rising warm air from the space. By drawing in the warmer air, the system can then cool it more effectively before redistributing it into the environment through the supply grilles, which are typically located lower in the room. This configuration utilizes the natural convection of air, creating a more balanced and efficient airflow throughout the space, leading to improved comfort and system performance.

In contrast, return grilles located at the floor level or on sidewalls lower down would not take advantage of the natural tendency of warm air to rise, potentially causing inefficiencies in air circulation and temperature stratification.