As fuel burns in a stove, it creates ash. You must remove the ash from time to time to keep your stove burning efficiently. Removing ash is known as "riddling", from the Latin word "cribrum", meaning "sieve". Some stoves are designed to burn wood, some to burn coal or coke, and some to burn all these fuels. When and how you riddle your stove depends upon the kind of fuel you burn.
A stove often has a "riddling plate", a grate in the floor of its firebox. When you shake the grate, ash and cinders drop out of the firebox and collect in an ash pan, housed in a separate compartment of the stove directly below. For wood-burning stoves with no riddling plate, hold an ash pan below the open door of the firebox and scrape the ash into it, using a long iron poker.
To burn well, solid fuels such as coal or coke need a steady stream of air from beneath the fire. The stove has vents or "dampers" to let in the air. It is often circular in shape and low down on the firebox or ash pan door. If ash builds up in the stove's firebox, it will block the flow of air from the dampers. Riddling removes the ash, allowing air to circulate freely.
Wood needs a stream of air from above the fire to burn well. Close the stove's lower dampers, usually by screwing them clockwise, and open a damper at the top of the stove door. Wood burns best by smouldering on a bed of hot ash, so do not riddle wood as it burns. Some stoves have a riddling plate you can close before laying a wood fire.
When to riddle
Riddle a solid fuel fire whenever you add more coke or coal, when the coals stop glowing, or when you can see a large build-up of grey ash inside the firebox. After the fire is out, riddle the ash again to clear the firebox, ready for laying a fresh fire. Riddle a wood fire only after it has burned out.
How to riddle
Some stoves have a handle on the outside, attached by a rod to the riddling plate inside. Pull the handle forward and back to agitate the riddling plate, shaking ash into the ash pan. Other stoves have a socket at the base. Fit a lever or "riddling bar" into the socket and move it up and down or from side to side to shake the riddling plate. Keep the stove door closed to stop ash flying out.
If your stove is in regular use, remove riddled ash from the ash pan once a day. Tip the ash into an iron bucket. Even ash left overnight that looks cold and grey will be very hot, so avoid touching it. Do not let hot ash build up in the pan until it reaches the underside of the firebox. Prolonged exposure to hot ash will damage the bars of the riddling plate.