A burning fire is exothermic because a lot of heat is given off as the wood is converted into carbon dioxide and water.
In an exothermic reaction, energy (in the form of heat) is released into the surroundings when the reactants are transformed into products. In the case of burning wood, the combustion process releases heat and light as the wood reacts with oxygen to form carbon dioxide and water. This release of heat is what makes burning a fire an exothermic reaction.