What is a half bath?

Any bathroom regardless of size will require access to fresh air, but not always from an exhaust fan. Building codes require any room with a toilet or bathtub to have some form of air exchange. In most homes, this is done with an exhaust fan. However, if the space already includes an openable window, an exhaust fan is not required. Obviously, this will not apply to half baths without an exterior wall. To be effective, exhaust fans must be capable of exchanging 50 cubic feet of air per minute, or more.