Why Is One Room Always Hotter Than the Rest?

Why the far room loses

Air follows the path of least resistance. The room at the end of the longest duct run, with the most bends, gets the least air — especially if that run is flexible duct that has been kinked or compressed in the attic. In San Diego County we see this constantly in homes where a room was added and tapped off an existing trunk that was never sized for it.

The return nobody thinks about

Air you push into a room has to get back out. A bedroom with a supply vent, no return, and a door that is usually closed will pressurise slightly and stop accepting air. Adding a return, a transfer grille, or even undercutting the door can fix a hot room without touching the equipment.

What actually fixes it

• Airflow balancing — adjusting dampers so the system delivers to the rooms that need it
• Adding returns and supplies where the original design left the room short
• Replacing crushed or undersized duct runs
• A ductless mini split for a converted garage, attic room or addition the duct system was never built to serve

When closing vents makes it worse

Closing vents in cool rooms to force air elsewhere raises static pressure across the whole system. That reduces total airflow, can freeze the coil, and stresses the blower. It is an understandable instinct and it usually backfires.