The object of this test was to determine possible causes of unsatisfactory service rendered by the airplane engine heater made by American Stove Co. This heater operates in a manner similar to an ordinary gasoline stove. Conclusions: 1. Only clean, high-test gasoline should be used. 2. The burners and all gasoline connections to burners must be kept clean, clear, and tight. 3. Removal of the fire screens must not be done while the heater is burning and in the hangar, as the exposure of the naked flame to the outside air may cause an explosion in the hangar or around the airplane. 4. The fire screens must be kept clean and free from dirt and soot. It is not recommended that any apparatus using a flame be allowed to operate in the hangar without competent attendants. The heaters should be inspected periodically to make sure their operation continues to be normal.