Category Archives: General knowledge

DEFRA Approved Stoves

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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.

Buying a new House ? What this could mean for you and for us.

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Just recently, we had a few new customers within a short period of time who had all recently bought a new property and wanted to start as they mean to go on by getting their chimneys swept and checked out. So far so good, it is a wise decision to get us in sooner rather than later when you are about to start decorating.

Often times when we get a call from a new owner like this, there may be a surprise or two waiting for us in the flue. When on initial inspection i find a bag, a bunch of newspapers or something else stuffed up inside the flue, it often turns out to be a sign i may be about to find something worse too. This could be anything from just an old dusty/really dirty lum to something like a collapse full of rubble, bad birds nest or even worse problems. It seems almost nobody thinks to take a torch to look up inside the flue and unfortunately this seems to include most of the surveyors that you pay so much money to for advice.

One of these new owners got a nasty, “surprise moving in present” which presented itself to me in the form of massive stalactites of burnt soot when i shone my torch up the flue. This immediately told me a few things about the previous owner. He had burnt his fire relentlessly over the years without getting it swept, to the point it had been badly on fire numerous times. He very obviously didn’t care about what he burned, maintenance, nor his or the new owners safety, .. or for that matter even a sense of fair play.


The actual bag blew off with the sheer amount of debris

For us the job easily entailed something like the effort of ten normal sweeps and also took about 6 or 7 times the length of time to do a normal sweep. A few hours later we were satisfied the chimney was swept to standard and after cleaning up, we were left with 4 full bin bags of burnt crispy soot (if this had been normal soot it would have been another 2 bags at least) on the hearth.


Several hours later


This job for me, easily won the ‘worst lum of Scotland’ award. It was without doubt the single worst job in my entire career since i took over from my father in 2012. There have been a few contenders from time to time but this won hands down, it was something else indeed.

Voila job complete ..finally, phew!

Unfortunately, for the new owners this was only a sample of the previous owners exceptionally nasty & careless character. They went on to tell us about numerous other nightmares plaguing the house that they had inherited after buying it. This old so and so had actually stolen all the electrical fixtures & fittings leaving sparking wires where the original light switches & sockets had been too, wow.

So, the moral of this story is be careful when you are buying a property folks. It is wise to get the sweep in to do his thing before thinking about decorating just in case there are problems in your flue too.

Buckled/Broken Baffle Plates

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It almost always comes as a shock to new wood burner or multi fuel stove owners that their baffle plate (also known as a throat or deflector plate) is classed as a stove ‘consumable’ and is therefore NOT covered under their stove warranty in the same way that most of the other components are.

This is because baffle plates are positioned at the top of the fire chamber specifically to deflect flames and heat back into the stove instead of letting them go straight through the flue system. And is partly why stoves are much more efficient at delivering heat to your room than an open fire.
However, it’s also why even on top quality stoves, baffle plates tend to burn out.

The Main Problem

Baffle plates are positioned at the hottest possible part of the stove and take the full brunt of the very high temperatures day-in and day-out. So whether your baffle plate is made of traditional cast iron, heavy steel plate, stainless steel or vermiculite board, you will eventually have to replace it.
How often this needs to happen depends on the type of fuel you burn, the size of the fuel load and how you burn your fuel.

Some stove owners can burn through their stove baffle plate in a matter of months and conversely some owners can make theirs last for years. A baffle plate on a boiler stove for example, will not tend to last as long as a baffle plate on a non-boiler stove. This is simply because boiler stoves generally need to be burned ‘harder’ over longer periods to maximise the heat to the hot water, especially when there are lots of central heating radiators connected to the system.
***As a matter of interest, smokeless mineral fuels (eg Anthracite Ovals) do not have the same flame height as an equivalent wood log load and can therefore be easier on a boiler stove baffle plate (but not necessarily on your CO2 emissions or our faces).***

The Consequences

If you regularly need to replace your stove baffle plate then you should review how you operate your stove by referring to your owners manual. It should contain advice on recommended fuel types and fuel loads, as well as instructions on how to effectively operate your stove. Quickly burning out a baffle plate means that you are probably not only wasting money on replacement baffle plates but also wasting money on fuel for sure.

***Chimney sweeps need to be able to remove the baffle plate so they can use the power sweeping equipment and clean effectively. *** If it is buckled and cannot be removed then I am in the unfortunate situation of having to charge a call out fee and you will need to call your installer out to remove & replace it.

Damaged baffle plates are increasingly more common these days, (which is one of the reasons for writing this article) creating speculation on the quality of metal materials nowadays. Also, often the installers fail to ensure the customer is sufficiently educated in the use and maintenance requirements of their appliance in the first place. Mostly though, it is users over filling beyond the stove load capacity.


The Cure

It is often the case that you are over loading and over-firing your stove and producing excess heat which is wasted through the flue system. An easy to use magnetic flue pipe thermometer will help you to monitor your flue gas temperature and can clearly indicate when you are over-firing your stove.

In my opinion a flue pipe thermometer is one of the best, ‘value for money’ stove accessories you could buy. It helps you to maximise the efficiency of your stove and also alerts you when your stove is potentially dangerous by being over or under fired.

It is very easy to abuse a stove and burn out a baffle plate within a single heating season by simply ignoring the manufacturer’s recommended fuels and operating instructions. Ergo, it’s also easy to see why most manufacturers now exclude baffle plates, fire grates, fire fences and glass from their normal warranty terms.

Figure 1 : Warped , corroded and finally broken Baffle plate

Figure 1 above shows a burned out cast iron baffle plate which is about three years old.

The owner used mainly softwood (it was free) which required a substantially bigger fuel load than the equivalent hardwood load needed to generate the same heat.

***This meant that the fuel and flames were too close to the baffle plate so the extremely high temperatures which were created, caused the baffle plate to warp and eventually fail (there is NO middle left).***

That particular stove had a rear fitted flue and it wasn’t until the owners noticed the flue pipe was glowing red that they realised they had any kind of problem.

Cool Fuel Rules

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There are many fuel types available to the solid fuel user: coal, peat, wood logs, compressed wood products, smokeless coals. With so much negative information in the press these days … which is the right fuel for you to burn?

Firstly , you must look at your appliance and follow the manufacturer guidelines as burning the wrong fuel type can be dangerous and at the very least invalidate your warranty. Good sweeps are generally a hive of knowledge.

If you care about the environment, then you would want to focus more on renewable fuels such as wood logs.

Selecting and purchasing wood logs

Ash and beech are some of the best woods logs to burn however most logs burn perfectly well (see our burning wood post) if they are dry enough and have been adequately seasoned.

Wood should be purchased from a reputable supplier who should have to comply to regulations and have a vested interest in planting more trees to replace what has been felled.

Wood logs must have less than 20% water content when they are burned. This can ascertained several ways, (see our post on moisture meters) but the easiest and probably most reliable at a price is to purchase logs from woodsure who will have done all checks and tested the moisture content in random batches. You will also be able to complain if the wood you purchased is too high in water content.

If you choose to purchase unseasoned logs then you must season them (typically for 18 months or more) and after seasoning you must test the moisture content with an electrical conductivity moisture tester prior to using them. (again for more on this see our post on moisture meters) Users burning wet wood are one of the biggest problems and challenges our industry faces but it is one of the easiest fixes too.

Why mixing fuels is a problem

Wood and coal burn quite differently. Wood burns through a process of gasification where the volatile oils within become heated, turn to a gas, mix with oxygen above the log and then eventually combust as a mixture of gases.

Coal on the other hand is primarily a carbon, to burn efficiently oxygen must enter and mix from below the fuel. Combustion takes place inside and not above the coal itself.

There are also distinct differences between wood and coal burning types of appliances, such as a grate below or just flat metal base.

Some issues associated with the incorrect use of fuels

  1. Wood on top of coal

If you try to burn wood on a bed of coal you would need to open the top air intake, thus drawing air above the coal and not through it from below. Therefore, the coal would burn poorly and produce high levels of carbon monoxide and carbon dioxide, which acts as a fire suppressant/extinguisher and the effect is compounded by the inadequate heat from the coal.
Wood burns by first emitting volatile hydrocarbons which then become gaseous.
Normally these hot gasses mix with oxygen and burn with the yellow flame we associate with wood. However, in the reduced oxygen environment above a coal bed the volatile gas emitted by the wood log will instead travel into the chimney where it then deposits as a flammable creosote.
Another issue is when combustion temperatures and oxygen levels are too low, then the later hotter stages of gaseous combustion will not effectively take place. During these later phases, carbon soot particles should be burned.
If these particles are not burned they will then exit the chimney as fine dust pollution harming our air quality with all the associated risks.

2. Coal on top of wood

So we understand that coal requires oxygen from below to burn effectively, think bellows in a foundry. If we burn wood below a coal bed we will have a situation where our coal is bathed in carbon dioxide leaving an incomplete burn. The second issue here is that wood produces lots of ash which in turn blocks the ash grate, further lowering the amount of available oxygen to the coal.
If the coal used is smokeless, such as anthracite then high levels of sulphurous compounds will also be emitted. These compounds are highly corrosive and will eat through stainless steel liners and most pot coverings in next to no time. The one exception to the wood underneath coal scenario, is when kindling a fire with wood. Here it is very likely that the air intakes or even the door will be open in order to provide enough oxygen for both fuels for a limited time.

Slumbering

The term slumbering describes the process of the user loading the already burning appliance and then closing down the air supply. This is in an attempt to make the fire burn for long periods, typically overnight.

The big problem here is the fact that fuel requires oxygen for combustion. When oxygen is limited in a combustion reaction, there are several results that occur as are shown below.

  • Much of the volatile content within the fuel is emitted due to the reduced heat but it does not combust. It rises up the flue coating the chimney with volatile fuel, greatly increasing the risk of chimney fire and the requirement for sweeping.
  • Carbon requires lots of oxygen and heat for the particles to combust. When the oxygen supply is limited, dangerous sized carbon particles are released. Many of these particles make it to the outside air as fine dust pollutants , polluting the environment and causing health problems such as respiratory and lung diseases.
  • Heat or the lack of. In order for a fuel to release its stored heat, it must react with oxygen, it being the catalyst for a combustion reaction.
  • Cost. Slumbering will shorten the life of stainless steel liners, increase the need for servicing, sweeping and maintenance. It will reduce the heat value that you should get from the fuel, making it less cost effective too.

In conclusion

Ideally you would only burn dry wood logs in an environment that has adequate air/O2 for moderate flaming combustion to take place. This is achieved by adjusting the air supply so that flames are not sucking up the chimney but not limited too much. Smoke should not be visible in the firebox, only in the fire.
Also by adding only as much fuel as is needed to fill the fire box with flames, because burning too much or too little fuel at a given time is another mistake to be avoided.

Your chimney sweep should give tips on fuels and how to achieve adequate flaming combustion, fuel storage, types, sweeping frequencies and many other important factors surrounding good use practices.