A system for a closed circuit forced hot air warmer of patient beds and blankets with improved sterility has a patient mattress or blanket microprocessor controlled warmer that circulates heated air in a closed system without releasing warmed air into the area surrounding the patient or into the operating room. The system helps to avoid the exposure of patients and hospital workers in the operating room to possible infecting microbes carried in unsterile turbulent air currents related to the release of air from non-closed systems. The machinery and flexible hoses of the system are initially sterilized by a microprocessor controlled antimicrobial mist generator. The system does not discharge jets of warmed air due to the closed circuit arrangement. Turbulent air flow previously produced in the vicinity of the patient by high velocity air jets is eliminated. An ambient, quiescent condition accorded by closed circuit heating prevents infection of patients and operating room personnel by microbe migration.