Certain difficulties of respiration and/or disturbances of bronchial secretory processes may be lessened, or relieved, when patients are enabled to breathe an atmosphere which has been conditioned to fulfill their special requirements. In acute or chronic conditions, or post-operatively, the siniultaneous control of air temperature, humidity, cleanliness and distribution may be advisable and, sometimes, essential. When such a therapeutic “climate” is provided, several different combinations of temperature, humidity and air movement may be found to produce the same feeling of warmth and comfort: these are thermoequiva1ents.l When ultrasonic mist fills the enclosure in which the patient breathes, the relative humidity is always 100%. Since this type of mist has come into increasing use, the variables now under consideration are those of temperature and air movement.2 Progress in the development of tent therapy has resulted in a variety of temperature regulation methods. The advent of the ultrasonic nebulizer, however, has made it possible to utilize two comfort producing cooling factors which formerly could not be exploited effectively : evaporation and convection. With the goal of providing a comfortable, practical and therapeutic breathing atmosphere for pediatric patients, a new approach was taken to canopy design. Examination and evaluation of evaporative and convective cooling mechanisms were undertaken. Ambient temperature and humidity ranges in the area surrounding therapy tents, as well as temperatures inside them, determine their influence on patient comfort.