Changing HVAC Duct work for the house?

Hello All


I am doing a whole-house renovation now, so opening some walls here and there. My contractor replaced the furnace and condenser in the house. The furnace is located in the attic, while the condenser is located on the balcony on the 1st floor.


The old furnace/condenser were both about 30 years old. I am not sure if the duct has been replaced but I assumed no.


Should I replaced the duct in the whole house? My contractor changed the duct in the attic and mentioned that the duct in the attic is the most important as there is large temperature fluctuation in the attic. He checked the duct through the house and said it's still in good condition with good insulation. He also mentioned that duct last a very long time.


I assumed when you replaced the HVAC system you would want to replace ALL the duct work? Should I replace it? Is he right? Thoughts?


My thoughts are given that I am renovating now, I should just replace it. My contractor thinks it's a waste of money.