I have a hvac system, with hot air being distributed to different parts of the house with seprate ducts from the furnace. My question is since I have unused rooms in the basement in which I keep the registers closed, does it make sense to install dampers or to cap the 6 inch ducts completely to save energy even more? Also I have coleman ducts and I'm not sure if they have already dampers, can anyone explain how they should look like, and how to operate them? Thanks

You can do more damage than good by shuting a register or duct off 100%. Your system is set up to move X amount of air(cfm) if you start shuting off air flow you have a chance of doing damage to the system or even costing you more money from a high amp draw from the blower motor and or compressor if it's a heatpump.