Question: how hot are coals in a wood fire

title: Ember
text: An ember is usually formed when a fire has only partially burnt a piece of fuel , and there is still usable chemical energy in that piece of fuel . Often this happens because the usable chemical energy is so deep into the center that air ( specifically oxygen ) does not reach it , therefore not causing combustion ( carbon - based fuel + O → CO + H O + C + other chemicals involved ) . It continues to stay hot and does not lose its thermal energy quickly because combustion is still happening at a low level . The small yellow , orange and red lights often seen among the embers are actually combustion . There just is not enough combustion happening at one time to create a flame . Once the embers are completely ' burned through ' , they are not carbon as is commonly believed ( carbon burns , and is not normally left behind ) , but rather various other oxidized minerals like calcium and phosphorus . At that point they are normally called ashes . See : Wood ash for more on the residue that is left .