Some are requiring a box per TV. No one can answer this correctly unless you provide more detail.
As to Eco issues, I added this thing -> http://www.amazon.com/Belkin-Conserve-Socket-Energy-Saving-Outlet/dp/B003P2UMQ2/
When the TV goes off, so does everything else!
What items does a residential home need to connect ALL their TV's to one cable box?
These Digital Converter Boxes are using excess electricity and I prefer using one box connecting all TV's. The boxes are not EcoFriendly.