A bedroom without an HVAC air return register may still experience some cooling or heating side effects when the whole house central heater/AC is running, although it may not receive the same level of conditioned air as rooms with dedicated air return registers. Here are a few factors to consider:
Airflow through door gaps: When the central HVAC system is running, air will be forced into the room through any gaps around doors or other openings. This can result in some degree of air circulation, though it may be less efficient than having a dedicated air return.
Pressure differentials: As conditioned air is supplied to other rooms with air registers, pressure differentials can be created within the house. This can cause air to move from areas of higher pressure (supply vents) to areas of lower pressure (such as the bedroom without a return register), resulting in some level of air movement and potential cooling or heating effects.
Air leakage: If there are any air leaks in the bedroom, such as gaps around windows, electrical outlets, or other openings, some conditioned air may find its way into the room. However, these effects will be relatively limited compared to having a direct air return.
It's important to note that without a dedicated air return register, the room may not receive the full benefits of the central HVAC system. The absence of a return register can lead to less efficient air circulation, potentially resulting in temperature differences and less effective cooling or heating. Additionally, rooms without proper air returns may experience poorer air quality and potential issues with humidity control.
If you find that a room without an air return register consistently lacks adequate cooling or heating, it may be worth considering alternative solutions, such as installing a transfer grille or seeking professional advice to improve air circulation within that room.