What to know
Equipment size is only one piece. Duct leakage, return air, insulation, sun, and door position can all create a stubborn hot room.
A hot room does not automatically mean the air conditioner is too small. If the rest of the house is comfortable, the first place to look is usually the path the air takes to and from that room.
A crushed duct, loose connection, closed damper, undersized return path, or strong afternoon sun can all change the room temperature. Even a clean filter and healthy system cannot overcome air that never reaches the space.
Before replacing equipment, compare airflow at the vents and look at the duct route, return-air path, insulation, and windows. Solving the distribution problem is often more useful than adding capacity.
