Why is one room always hotter than the others?

Uneven temperatures are usually caused by poor insulation, leaky windows or ducts, an undersized or oversized HVAC system, blocked vents, or a room's exposure to afternoon sun. Rooms on the second floor, above garages, or with large west-facing windows are especially prone to overheating. Closing blinds, checking for blocked vents, and having a professional inspect your ductwork and insulation can help identify the root cause.