HVAC (Heating, Ventilation, and Air Conditioning) encompasses the systems and technologies that control indoor temperature, humidity, and air quality in buildings. Heating systems (furnaces, boilers, heat pumps) warm buildings in winter, air conditioning systems cool them in summer, and ventilation systems exchange indoor and outdoor air to maintain freshness and remove pollutants. Modern HVAC includes sophisticated controls, air filtration, humidity management, and energy recovery systems. HVAC represents a major portion of building energy consumption and operating costs, making efficiency a priority. Building codes set minimum HVAC standards for energy efficiency and ventilation rates. Municipal buildings require appropriate HVAC for occupant comfort and health, with system choices affecting long-term operating costs and emissions. The COVID-19 pandemic highlighted ventilation's role in indoor air quality and disease transmission. HVAC system decisions involve balancing comfort, energy efficiency, maintenance requirements, and capital costs over equipment lifespans.