I have seen many questions about fog machines, and even seen some in shows. I don't know if I am reading the questions wrong or if there is a misconception. Fog machines create quick think fog, that only last for seconds. This is not what you want for the fog that fills the room.
A haze machine will give you the mystic look, and fill the room, as think as you want, and will not 'vanish' right away. It takes a while for it to dissipate.
Ofcourse, hazers cost more, but do a better job at filling the room.
If you have any questions about these, ask them. I use both of these machines, fog and hazers.