If a bedroom does not have an HVAC air return register, it may still experience some level of cooling or heating side effects when the whole-house central heater/AC is running. Here are a few factors to consider:
Airflow: When the central heater or AC system is running, air is pushed into the various supply registers throughout the house. This supply air will naturally seek a return path to the HVAC system, even if there is no dedicated return register in the bedroom. The air will find alternative pathways, such as gaps under doors, unsealed ductwork, or other openings. This can result in some level of air circulation between the room and the HVAC system.
Pressure differentials: As air is supplied into the rooms with supply registers, it creates a pressure difference. This pressure difference can cause air movement within the house, and some of it may reach the bedroom even without a dedicated return register. However, the airflow and temperature control in the bedroom may not be as effective as in rooms with dedicated returns.
Temperature differences: Without a return register, the bedroom may experience temperature variations compared to other rooms. The lack of a dedicated return can limit the efficiency of air circulation and temperature equalization throughout the house. As a result, the bedroom may be slightly warmer or cooler than other rooms, depending on whether the heater or AC is running.
Comfort considerations: The absence of a return register in the bedroom can affect the overall comfort level. Bedrooms typically benefit from having a dedicated return register to help remove stale air, control humidity levels, and maintain a more consistent temperature. Without a dedicated return, the bedroom may feel less comfortable, and there may be a reduced ability to control air quality and temperature in that specific room.
In summary, while a bedroom without an HVAC air return register may still experience some indirect cooling or heating effects when the central heater/AC is running, the efficiency and level of comfort may be compromised. If you have concerns about temperature control or air circulation in the bedroom, it is recommended to consult with an HVAC professional who can evaluate your specific setup and provide recommendations for improving airflow and comfort in the room.