If I recall, heat pumps use a slower speed on the blower to move the air in heat mode. That could be something to look at too. A suction pressure reading would be of benefit. Hence get a technician to sort it out. I have a smaller Fridgedaire with an 1800 sq ft house and it works just dandy. I must further confess that I once installed a blower fan backwards and it did manage to move air..... just not nearly as much as it shoulc have.