The 4 C’s of HVAC are Comfort, Cost, Convenience, and Control. Comfort refers to the temperature, humidity, and air quality of the environment. Cost is the amount of money spent on energy and maintenance of the HVAC system. Convenience is the ease of use and accessibility of the system. Finally, Control is the ability to adjust the system to meet the desired comfort level. All four of these components are essential for a successful HVAC system.