I have a wall mounted mini split (Fujitsu 9,000 BTU) installed in my bedroom over my bed, intended to heat and cool my upstairs (there has no suitable location in the hallway). It is a standard sized bedroom, and the heat pump does an excellent job cooling and heating the room (I can get the room down to 60F on a hot day). However, here is the issue - the cooled or heated air will not leave the room. The doorway is about 10 feet away and you can feel it blowing if you stand in the threshold, but the airflow makes a dead stop there. I have tried pointing the air at different heights and even tried putting a fan in the door way to push it along, but nothing seems to work (heat seems to flow a bit better than the AC air). The installer has ensured me that the heat pump has plenty power for the job and it is an air pressure issue?? Any help would be greatly appreciated.
You are trying to force air from one room into another through a large open space. The problem is, you're not actually creating any pressure differential. The air in your room is being moved around by the unit but not being pressurized. The unit in your room creates a low pressure point and a high pressure point and the air moves around the room stirring up the air and creating an equalization of temperatures within the room.
So the air in your room is blown towards the door at an extremely low pressure. The air in your hallway is stationary (for the most part) and at the same pressure as the air in your room. There's really no force behind the air in your room to dislodge the air in the hall, and the air in the hall also has nowhere to go.
Forced air systems work because they have both air outputs and air returns - the returns serve to carry air needing heating/cooling back but doing so also creates that critical pressure differential needed for air to move from room to room.
Otherwise it's like the picture above the air sits next to each other, mixing only very slowly.