Updating duct work
If you see any irregularities or temperature variations, it may be a sign of eroding ductwork.
Aiming to replace your HVAC system before it actually fails will ensure that you have time to price and research options.
However, if the poor quality materials were used or shortcuts were taken during installation of ductwork, it may not even last this long.
Inspect exposed ducts in areas such as crawl spaces and attics to find out any holes or tears.
You should also look out for disconnected joints or eroded duct tape.
Visit each room of the house when the HVAC system is running and see if the air flow is proper at all places.