hey hey QWire, I suggest to try the search function on answerhub next time as this is a very often recurring question.
In Cascade, Click in the Black area outside of your emitter module list and then go to the details panel and Find the Fixed Bounds settings, and increase / decrease the bounds as necessary, in your case you will want to make the rooms size the fixed bounds of the system, or approximate as the center of the system is always the center of the bounds so if your fire is on a wall you may want to increase the bounds only in the direction needed to fill you room.