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

Safety first: Most work is at registers and ducts; turn off power if removing panels.

• Adjust registers: Slightly close registers in overheated rooms and fully open those in cold rooms.
• Inspect ducts: In accessible areas, check for disconnected or crushed ducts and repair or replace as needed.
• Seal leaks: Use mastic or UL-listed foil tape to seal visible duct leaks, especially near the furnace plenum.
• Blower settings: A technician can adjust blower speed taps or ECM profiles to improve distribution.

Severe imbalance may require duct redesign or zoning.