Almost all stoves manufactured in this day and age come DEFRA approved as standard as most built up areas like York, Harrogate and Selby are densely populated, meaning that poor air quality can negative effect on a large population, Having a stove that is DEFRA approved basically means that the air controls will always permanently stay open a very small amount even when you close the air controls down. This is to stop you slumbering the stove which in turn helps create less PM2.5 Matter and other nasty pollutants, helping us achieve a cleaner, greener world.