A Defra Approved stove , or more accurately termed a ‘Defra Smoke Exempt Appliance’ , is a wood burning stove which has 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 normal operation.
Defra Approved stoves have 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 without creating smoky combustion.
A Defra approved stove will 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 (1952). Using a Defra approved wood burner will allow you to burn wood legally in any UK Smoke Control Area .. which most of the UK’s cities and large towns now belong to.
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 classified as a Smoke Control Area , then in order not to break the law and risk being fined , 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 friendly since (if operated correctly) , it cannot produce nuisance smoke. It will also usually mean that your chimney and flue system stay cleaner for a lot longer.
Smaller liners are easier to fit and cheaper
If your 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) if you choose a Defra Approved 5kW stove you can also fit a 5″ (125mm) liner rather than the wider and more expensive standard 6″ (150mm) saving yourself some money on the liner.
In addition , it means that the narrower liner will be easier to fit and could also be useful where the chimney stack is very old and non-standard and/or where the liner’s route has some awkward bends. This solution is acceptable by both HETAS and Building Control.
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 burn other fuels using a Defra approved stove ?
If the Defra Approved stove is also a multi fuel stove , then provided you choose an approved smokeless fuel from Defra’s list such as Anthracite ovals 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 which stops 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 [and chimney sweeps] 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 and its’ 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 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 use 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.