Furnace runs but some rooms are cold while others are warm.

Safety: Use caution when accessing attics or crawlspaces.

Steps:

• Check registers: Ensure supply registers in cold rooms are fully open and not blocked.
• Inspect accessible ducts: Look for disconnected, crushed, or kinked flex ducts and repair or replace as needed.
• Adjust dampers: If manual dampers are present on duct branches, partially close dampers to warmer rooms and open to colder rooms to balance airflow.

For persistent imbalance, a professional should perform a duct design and airflow analysis.