A closed loop heat therapy blanket provided for warming a patient to prevent or treat hypothermia. The closed loop heat therapy blanket includes first and second sheets secured to each other such as to define a supply manifold, at least one supply duct, a return manifold and a return duct. The first sheet defines a supply inlet opening into the supply manifold and a return outlet opening from the return duct. Heated air is introduced into the supply manifold and travels through to the return outlet and through an outlet hose. As the heated air travels through the blanket, a portion is communicated through the second sheet and toward the patient. A heat source is provided for collecting and heating ambient air, and for collecting preheated air from the outlet hose. In one embodiment, a humidifier is provided for controlling the moisture in the air being directed toward the patient.