You need a grate in your stove to burn coal which means that you need a multifuel stove. Nearly all multifuel stoves are designed to burn wood, coal, peat and other fuels. The grate in a stove is made up of bars of metal (nearly always cast iron) with gaps in between them. The bars may be fixed into one rigid unit or be separate and sit in a frame inside the stove. The gaps between the bars let air from below get to the coal. This also helps stop the grate bars getting too hot - they can get damaged otherwise.
You need to make sure that the grate remains unblocked and that the ash in the ashpan does not come too close to the bottom of the grate or it will restrict the flow of air to the stove and your grate may get too hot and become damaged.
Most multifuel stoves have a riddling mechanism. This is a method which lets you move the grate in the stove from the outside so as to shake any ash that is blocking the grate down, through the gaps in the grate, and into the ashpan. Riddling usually works either by moving alternate grate bars up and down, by rotating a circular portion of the grate, or by letting you directly shake the whole grate. Some stoves have a fixed (non riddling) grate. In this case you have to poke at the fire with a poker to clear the grate of ash.
We do not recommend that you burn wood and coal at the same time: burning coal produces sulphuric acid and wood can contain a lot of moisture - this combination can coat your chimney in sulphuric acid solution which can quickly eat away at anything.
Plus the conditions for burning wood efficiently are not the same as those for burning coal efficiently.
When burning coal shut down the top air vent of your stove and use the bottom aur vent to regulate the fire. If this makes the fire die down too much then it sounds like the draw on your chimney is not that good. In this case use the top air vent too and consider contacting us to see how you could improve the draw on your chimney.
Coal is one of the vast stores of CO2 on the planet. Burning coal increases atmospheric CO2 which causes* global warming. The global temperature has already risen by 0.74 °C since 1900. Read more about how coal is a fossil fuel.
You might be interested in how to burn wood on a stove.
* = > 90% likely