This depends entirely on how much you are operating your wood woodheater. While there is no hard-and-fast rule on how often to remove the ashes from the firebox, it is recommended that you remove the ashes before they are at a level that they may spill from the firebox. It is also worth noting that it is beneficial to leave about 1-inch of ash on the floor of your firebox. This can help to insulate the firebox and gain more efficiency during igniting the fire.