Good quality coal is currently about £20.00 for 20kgs there are cheaper coals, you will get a lot more ash and a lot less heat. For an average stove this should last about a week, just a few smallish shovels in the morning to get a good base should be enough for a day, then you can load up for overnight burning, if you do this close down the primary air, if the stove has gone out overnight, it’s because you have a good draw on your chimney and you may need to slow down the air flow! It is important that wood is dry, a 20% moisture content is recommended, silver birch gives off good heat, but Ash and Oak are slower burning, therefore last longer. I have attached a separate sheet with more information on the properties of different types of wood.
– William Evans