A Defra Approved stove, or to give it the correct name, a Defra Smoke Exempt Appliance, is a wood burning stove which has been tested and passed the UK Government's Department of Environment, Farming and Rural Affairs (Defra) criteria for emission levels and the amount of smoke that it will be allowed to produce during all stages of normal operation.
Generally, a 'Defra Approved' stove has been modified by the manufacturer to limit the amount that it can be 'closed down' or in other words, by how much it can be starved of air which creates smoky combustion.
A Defra Approved stove will therefore always provide the minimum level of combustion air so that the wood burns efficiently without producing unnecessary smoke, thus ensuring that the appliance complies with the Clean Air Act. A Defra Approved wood burner will therefore allow you to burn wood legally in a UK Smoke Control Area – most of the UK's cities and large towns.