Furnace runs but some rooms are too hot while others are too cold.

Safety: Be cautious when accessing attic or crawlspace ducts.

• Register adjustment: Slightly close registers in overheated rooms and fully open in cold rooms. Do not close too many, as this can raise static pressure.
• Check dampers: If there are manual dampers on branch ducts, adjust them to balance airflow.
• Inspect ducts: Look for disconnected or crushed flex ducts, especially to cold rooms.
• Professional balancing: For persistent issues, have a contractor perform airflow measurements and balancing.