HVAC systems are divided into two main categories: forced air systems and hydronic systems. Forced air systems use a blower to circulate air through ducts, while hydronic systems use a pump to circulate heated or cooled water through pipes. Forced air systems are the most common type of HVAC system and are used to heat and cool homes and businesses. They are typically powered by natural gas, oil, or electricity. Hydronic systems are typically used in larger commercial buildings and are powered by steam, hot water, or chilled water. Both systems are designed to provide efficient and comfortable heating and cooling.