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.
Images: The Defra Approved Logo and the Defra Approved Hi-Flame Olymberyl Baby Gabriel
Why should I buy a Defra approved stove?
If you want to burn wood and you live in a UK city or large town, which is also classified as a Smoke Control Area, then in order not to break the law and risk a hefty fine, you must use a Defra Smoke Exempt Appliance. This is a wood burner which has been modified to pass the stringent Defra emissions tests which limit the amount of smoke that the appliance can make. However, wherever you live, a Defra Approved wood burner is a very good idea anyway because it is more environmentally and neighbour friendly since, if operated correctly, it can't produce nuisance smoke. It will also usually mean that your chimney and flue system stay cleaner for a lot longer.
If the chimney is going to be lined with stainless steel twin wall flexible liner and you plan on using a 5kW stove, virtually all of which feature 5" (125mm) flue outlets, then if you specify a Defra Approved 5kW stove you can also fit a 5" (125mm) liner rather than the wider, more expensive and standard 6" (150mm) thus saving yourself some money. In addition, it generally means that the narrower liner will be easier to fit and could also be worth considering where the chimney stack is very old and non-standard or where the liner's route has some awkward bends. This solution is acceptable by both Hetas and Building Control. On the odd occasion where The Stove Yard installers have encountered such problems when attempting to fit the standard 6" (150mm) liner we have up-rated the stove to a Defra Approved 5kw stove and solved any snagging problems by subsequently using 5" (125mm) liner. Of course if you need a bigger stove than a 5kW then it is important to note that they nearly always have a 6" (150mm) flue outlet and must, for safety reasons, always use a 6" (150mm) liner. It is both dangerous and an infringement of Building Regulations Document J to reduce it.
Can I use a Defra approved stove to burn other fuels?
If the Defra Approved or Defra Smoke Exempt Stove is also a multi fuel stove, for example like the famous Morso 1412 Squirrel or Hi-Flame's popular Precision II, then provided you choose an Approved Smokeless Fuel from Defra's list, like a smokeless Anthracite oval, and the stove manufacturer's manual also says that such fuels are not prohibited, then the answer is 'yes'. However, burning damp wood or other wet fuel will create nuisance smoke and, irrespective of whether or not the stove is Defra Approved, you will be in breach of the Clean Air Act and risk prosecution if you cause excessive smoke which upsets your neighbours.
What is different about a Defra approved stove?
From the outside, nothing. It's only the unseen combustion air control mechanism, usually inside the top front, underneath the base of the fire box or on the rear that is different. It will usually have been modified to allow a small continuous amount of combustion air through to the fuel to stop it smouldering when the air controls are, or appear to be, fully closed. Since the Defra tests are only concerned with wood, then this modification is generally undertaken to the secondary air inlet. Due to the expense of putting a wood burner through the stringent Defra tests some manufacturers, who sell two versions of the same model, will often charge more for the Defra approved model to cover their test costs. Other manufacturers will sell an additional Smoke Exempt compliance kit or propose that an adjustment is carried out by the installer. However, it is important to understand that you will be breaking the law if you burn wood and the kit has not been fitted or the adjustment has not been made to your stove if you live in a Smoke Control Area. The kit or the adjustment are simply not options that you can do without in this instance.
Is it better to choose a Defra approved stove?
A Defra Approved stove is going to be cleaner burning overall because it's hard to make the wood fuel smoulder and smoke since it cannot ever be completely starved of air. This is good for the quality of the air that we all breath and particularly good at keeping our neighbours happy. It's also good for your chimney or flue system because the stove is producing less smoke and therefore producing less soot, so that your stove's flueway (above the baffle plate and just before the flue outlet) and your flue system are a lot less likely to get clogged up.
However, if you intend to slumber burn with wood fuel to extend the burn time (eg overnight) then a Defra Approved stove will not offer you the same burn time as a non-Defra Approved equivalent. This is because a minimum amount of combustion air will always be delivered to keep the fuel from the smoky smouldering that is associated with slumber burning. Even if you swapped fuel to a smokeless coal for overnight burning and were using a multi fuel Defra Approved stove then the continuous supply of secondary air required for the configuration would still significantly curb the burn time of the smokeless coal. That is not to say that Defra Approved stoves are inefficient, quite the reverse. They stove ensure that enough combustion air is continuously supplied to make the wood burn effectively throughout the whole burn cycle.Of course If you live in a Smoke Control Area and you want to burn wood, then you don't have the choice.
Can I fit a non-Defra approved stove in a smoke control area?
The answer is yes, but you can only burn Defra Approved Smokeless Fuels and unfortunately wood isn't one of them. That means burning a naturally smokeless fuel like Anthracite or one of the many brands of manufactured smokeless ovals such as Homefire or Ancit. A full list is available by clicking on to the Defra website here.