The difference between carpenter bees and bumble bees is that carpenter bees upper surface of their abdomens is bare and shiny black in color while a bumble bees have hairy abdomens and some yellow markings.
Bumble Bees and Carpenter Bees are a bit similar but that's how you can tell the difference between a bumble bee and a carpenter bee.
Just take a look at the bees abdomen. If the abdomen is hairy then it's a bumble bee.