An HVAC system comprises all the equipment and infrastructure that heats, cools, and ventilates a building. System components include: heating equipment (furnaces burning gas or oil, boilers for radiator systems, or heat pumps), cooling equipment (central air conditioners or heat pumps in cooling mode), air handling units that move conditioned air, ductwork distributing air to spaces, thermostats and controls managing system operation, and ventilation equipment bringing in fresh outdoor air. Commercial and institutional buildings often have more complex systems than residential buildings, possibly including rooftop units, chilled water plants, variable air volume systems, and building automation systems coordinating multiple components. HVAC system design considers climate, building use, occupancy patterns, and energy costs. Proper maintenance is essential for efficiency, air quality, and system longevity. HVAC system upgrades in municipal buildings can significantly reduce energy costs and emissions.