PLACE OF BUSINESS
Scrooge's counting-house is described as the place where he works, with the door open so he can keep an eye on his clerk.
COUNTING-HOUSE
Once upon a time--of all the good days in the year, on Christmas Eve--old Scrooge sat busy in his counting-house. ... The door of Scrooge's counting-house was open, that he might keep his eye upon his clerk, who in a dismal little cell beyond, a sort of tank, was copying letters.