- Abstract Room air-conditioner operation was studied in order to understand how energy consumption and peak power demand are determined by user needs, concepts, and behavior. In a multi-family building in New Jersey, thirteen room air conditioners were instrumented in eight apartments, and the residents were interviewed about their cooling needs, decisions about when to turn on their air-conditioning, and their conceptions and operationsof the units. Residents were not billed separately for electricity. They nevertheless limited their use of air-conditioning on the basis of many non-economic factors, including: daily schedule, folk theories about how air conditioners function and the body's heat tolerance, personal strategies for dealing with all machines, and beliefs and preferences concerning health, thermal comport, and alternative cooling strategies. Across physically similar apartments, seasonal air-conditioner energy consumption varied by two to three orders of magnitude while interior temperature varied by only 2.4 °C to 3.7 °C (4.3–6.7 °F). The least-frequent users were effectively achieving comport at greatly reduced energy consumption, but they were not reducing peak demand since they ran their units only on peak hours of the hottest days of the summer. Three-quarters of the residents did not use their thermostats, controlling cooling instead by switching their units on and off manually. Only one resident consistently let his air conditioner operate thermostatically, and many were not aware that their units had thermostats. The prevailing non-thermostatic mode was initially thought to indicate a need for user education. Further investigation suggests that the cause is in fact a startling mismatch of existing room air-conditioner controls to user needs, with a corresponding opportunity for fundamental redesign of controls.