If fresh fuel is not heated, then a fire cannot spread. The effects of fire result from the movement of heat away from the flame and into an adjacent area, where there is fresh fuel. Take the heat away and the fire goes out. Fires also transfer heat by radiation to the surroundings. When a fire starts in a room, the hot smoke cannot escape very easily.
Heat is transferred from the fire to the smoke by convection.
Heat is transferred from the smoke to the ceiling and the walls by convection. The fire radiates heat outwards to the rest of the room. The hot smoke radiates heat downwards to the floor and the rest of the material in the room. All these process of heat transfer are shown in the figure below. The heat in a fire causes the fuel to decompose into simpler components.