My dog is casting hair excessively!!! help.?

My 18month old female Rottweiler is casting hair excessively, she recently became an indoor dog after being outside for around a year. Meed to hoover daily, sometimes twice daily due to the amount of hair being shed. Her general health is very good, and she is very active is this just normal as of change of living enviroment, or is this a health problem? ? Please Help.