Over time a building's interior may have been reconfigured, new equipment installed, or population densities changed. Rebalancing usually involves adjustments of air dampers, air handling unit motor speeds, and removing or modifying partitions or obstructions that block air, as well as other devices that create pressure differentials between rooms. Rebalancing not only improves air flow and can reduce the hot and cold spots, but also reduces energy costs and more than pays for itself through subsequent energy savings.