A hot air draft would shut the hp off prematurely...not make it run longer. The stat should be 5 ft off the floor and close to your return grill, but not in a dead-air space(hallway),or in a direct path of a supply grill or heat source(window,near a stove, fireplace,outside door,etc). It hard to tell the best place without being there, this is what your installer should have determined.