Introduced in 1998, the IECC addresses energy efficiency on several fronts including cost savings, reduced energy usage, conservation of natural resources and the impact of energy usage on the environment. Important changes in this sixth edition include: A comprehensive set of changes includes measures to improve the thermal envelope, HVAC systems and electrical systems of residential buildings up to three stories in height. Commercial enhancements include required energy savings for windows, doors and skylights; thermal envelope efficiency; and increased efficiencies for installed HVAC equipment.