Generally, trying to move hot air with more fans is not productive, and usually just cools the hot air down. Creating a passive convection current is much more effective. When you remove air from a room (like with a fan) you create negative pressure, causing air to flow back in (if air leaves, it needs to be replaced). Placing a box fan in the doorway on the floor sucking the cold air out will create negative pressure and cause warm air to flow into the bedroom. This is my experience with heating with coal.