Category Archives: Stoves

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.

Stainless Steel Flexible Liners & Smokeless fuels: What you need to know.

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Occasionally a chimney flue will be in such a bad condition that a liner will be required. This might be due in part to the age of the building but is definitely more to do with the user (or abuser as the case may be) of the flue: as in what they burn, how often and how they burn it.

Prior to the 1950’s , the mortar between the bricks generally consists of old sand and lime material mixes. This tends to disintegrate and dissolve away when the sulphur in the soot mixes with water to create Sulphurous acid (H2S03) which is [NB/only one oxygen away from Sulphuric acid (H2SO4) ] pretty acidic stuff. It is also responsible for the acid rain effects environmentalists have been banging on about for a few decades now.

All coal contains sulphur in it to a greater or lesser extent , with the higher (smokeless) grades having much more & often halogens too unfortunately. I personally , have seen a china hat I fitted to a flue that uses only smokeless fuel last just 18 months (these often last more than 10 years in other conditions) before it fell to pieces.
As a sweep , for me personally it doesn’t take very long to realise I am sweeping a smokeless burning appliance. After the stuff gets on my face , I can literally count to 30 before my skin feels like it is melting off , the soot is indeed horrible stuff to a chimney sweeps skin complexion , never mind his health if inhaled.

However , on the plus side smokeless fuel does create a lot less soot & other pollutions overall.
It can be useful when used occasionally on very dirty open fires. Fires that burn lots of cheap house (bituminous) coal and/or a lot of wood too can benefit by using an odd bag here & there (such as one bag per season) as it reduces the soot volume by aggregating it together.

Chimney Liners

Chimney liners come in many forms , for example in the USA most chimneys are ceramic block types that are rectangular and slot together. Here in the UK some are concrete tubes that have been poured and allowed to set. Furan-Flex liners are made of a polymer type material which has a 25 year life time guarantee but being expensive is not very common , I have never come across one yet. You may often see twin wall (shiny steel or matt black) rigid pipe sticking out of an external wall or through a roof. All liners have their own properties and as such , pros and cons or strengths and weaknesses.

For the most part here in the UK though , flexible Copex style stainless steel liners which come in 2 grades are used. The 316 which is suggested for use in wood burning only stoves and the 904 which is suggested for multifuel stoves. If you don’t know what the difference between wood burning and multifuel types of stoves are , you can read about them here in our previous article from 2015. Although these stainless steel liners are suggested for use in stoves , they are occasionally found in normal open fires too. In this case they are often connected to a hood up inside the fireplace which looks & acts as a fume collector not unlike the hoods you often see above kitchen cookers.

These types of stainless steel liners are composed of two layers an INSIDE and OUTSIDE layer so not all are made the same (read on to Schiedel information below).
Some liners are 904 with an external layer of 316 on the outside. The inner 904 protects from corrosives (found in smoke and gases) whilst the outer 316 is a solid extra barrier to rust from a damp chimney. I would always choose a liner with a 904 internal core but I appreciate that finances can dictate decisions and a 316 grade internal core is not necessarily a poor choice if you intend to only burn dry hard wood.

Stainless Steel Grades

The difference is purely one of quality. The 904 grade is a higher grade of stainless steel than the 316 grade and is less likely over time to corrode from the inside. The terms 904 and 316 are terms used within the stainless steel industry and are not peculiar to just the wood-burning stove market.
If you do not want to read any further: just choose the 904 grade high quality flue liner especially if you are a “heavy user” and DEFINITELY IF you are going to burn smokeless fuel. Choose the 316 grade flue liner if you are on a budget and you intend to burn ONLY seasoned (dry) wood as a light to medium user.

As I said above in the opening paragraph , the state of your flue is more to do with the user/abuser as the case may be , liners do not last for ever. Even if just burning wood which is damp or with paint on the surface , the dampness & corrosives from the paint will shorten the life of the liner quite dramatically.

Definitely choose 904 grade chimney flue liner if you are installing a boiler stove because it is more likely to be slumbered overnight and when slumbering , less of the nasties in the gases are burned away.
Any stove that is likely to be slumbered will benefit from a 904 grade liner **(slumbering is when you turn the air supply right down until the fire is almost going out but not quite and is NOT recommended nor is shutting off exhaust vents by use of a damper plate in the flue pipe, for many reasons but mainly because it is blocking the monoxide escape path!)**.
Slumbering is also bad for the environment , puts you at risk from monoxide and tars up your flue , so your chimney sweep won’t be too happy either.

Different manufacturers offer different guarantees on liners. Those with a 904 core get a longer guarantee than a liner with a 316 core , generally 25 or 30 years as opposed to 15 years as a rule.

***However , don’t get too excited about the guarantees: if your liner does get damaged in less that time then it is probably likely YOU have done something wrong and manufacturer’s can , if they wish prove this with tests. So this kind of situation can quickly descend into a blame game.***

You should get your liner swept regularly (your chimney sweep can help by producing their records to show this if required) and take all possible precautions (burn a correct fuel , in the correct way , have a china hat fitted to deflect rain and use ALL other measures to avoid dampness in your flue) to ensure your liner is protected.
**Even if a manufacturer does replace your liner , they are not going to pay for any labour or scaffolding costs which is often the greater expense in these matters**.

Not all liners are made the same

Liners with a 904 core should last considerably longer than liners with a 316 core , although some sweeps would definitely disagree with that statement and are of the opinion there is not much difference between the two grades of steel , especially once corrosion has set in.
NB// Bear in mind not all liners are made the same so it always pays to buy a better quality brand than a cheapo version!!
Also , DIYers do NOT be tempted to try to save money by using a Gas fire liner on a solid fuel appliance , as they are single cored and are in no way rated for solid fuel use.



The German Connection

In the chimney sweeping world you would be hard pressed to find any country more obsessed with high standards than Germany. The Schornsteinfeger is quite an important person and indeed has a lot of power as you can see here in Wikipedia.


The award-winning German chimney component manufacturer Schiedel and its premium TecnoFlex liner is widely used by HETAS and Oftec installers all over the UK. Formed in a completely different way than most other liners , TecnoFlex has an unbreakable lock between layers which prevents it from pulling apart and keeps the inside super smooth for easy down drainage of condensates. This super smooth layer also helps prevent soot and tar from building up on the inside of the liner potentially preventing blockages. Schiedel liner material is imported from Germany and finished off here in the UK by skilled technicians.

They make and sell the highest grade liner sold in the UK – 904/904 grade liner – NOT 904/316 like many other manufacturers – which is perfect for wood and smokeless coal burning but NOT at the same time !!!

Why?? because the moisture in the wood will mix with the sulphur in the coal soot creating sulphurous acid…. remember ??

Condensation and Other Issues that show up in cold weather.

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At this time of year when the weather gets cold enough to start affecting your fire or stove you may be surprised or even shocked when things don’t seem to work the way they normally do.

Appliances have Running Temperatures

Stoves, indeed all appliances have a running temperature and it takes time to reach this point, so you may find they won’t start up so easily and/or are Smokey for the first 10-15 minutes. This is due to the cold air dropping down the flue and stopping the updraft of hot air trying to rise but once up to running temp the hot air rising displaces the cold air as it pushes its way up and out the chimney flue.

One way to overcome this problem is to try heating the metal baffle plate with a blow torch before attempting to light your fire. Or if it is not metal, you could try the Scandinavian method of building your fire kindling upside down i.e. paper on top> kindling>wood/coal.
** NB// This updraft problem is particularly prevalent in flues on the gable end of your building and if the flue space is big too, then you may need to have your liner wrapped in an insulation jacket or the flue space backfilled with vermiculite. **

Tar or Black Liquid Formation

Recently, a customer called worried about black liquid tar coming down into their stove. You too may have found a sticky, black liquid in your wood-burning stove and you might have spotted it running down the inside walls of your appliance or settled somewhere in the firebox. The consistency reminds you of tar because that is exactly what it is.

If you have seen this black liquid, it indicates that you are not operating your stove correctly and in particular , burning unsuitable (damp) fuel.

Usually tar is created as a by-product of burning logs on a wood burner when the moisture level of the wood is too high. Since energy is being wasted evaporating water, the stove doesn’t get up to a high enough temperature, which leads to cooler gases going up your chimney. Since they are cooler, they are prone to condense when they touch the cold metal of the flue liner.

The condensed gases will either solidify on the inside or the flue or start to drip back down into the stove in the form of the sticky liquid. Whenever the tar does get the chance to solidify it will turn into creosote. A build-up of highly flammable creosote in your stove system significantly increases the risk of chimney fires. This is especially true if you burn soft wood such as pine, the resin being the main culprit.

How to stop the black liquid appearing in your wood burner

There are a few ways to stop the black liquid appearing in your wood-burning stove. The first is to ensure that the only logs you burn are ones that have been correctly seasoned and have low moisture content (<15-20%), this is easily achieved by using a moisture meter.

Ensuring there is a strong draw up your chimney, operating your stove at full capacity and burning it with the air intake fully open for 10-15 minutes once or twice a day will blast off the vapor and burn any sediment that settles on the flue. You can also try using some table salt on the burning wood to try to help absorb any water that is created. Finally, not slumbering your stove over night and also ensuring your room is well ventilated (especially if you keep damp logs in the room too) will minimise the chance of flue gases condensing in your chimney.

It is also important to get your chimney swept regularly as this will remove any residual creosote that has built up in your chimney and prevent it seeping back down your chimney and into the stove. Regular sweeping will also protect your liner from corrosion and eventual destruction.

Reasons for regular maintenance of stoves and the risks of neglect.

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Any kind of appliance that does something with moving parts and especially those exposed to high temperatures , will need to be maintained regularly.
When it comes to maintenance people can normally be divided into three kinds:
1. Those that know , understand and appreciate the situation and whom will maintain their devices/appliances.
2. Those that know but think they can ‘risk it’ one more time.
3. Those who are just simply not aware. [Installers to blame here?]

Once you own a wood burning stove you become responsible to ensure it works safely , burns cleanly and hopefully lasts as long as possible. Unfortunately , many stove owners are unaware of the basic requirements needed to ensure it all keeps working correctly.

Wood burning stove maintenance

Stove maintenance can be broken down into three distinct sections. Much of the daily maintenance can be handled by the owner but some of the more complex maintenance will require professional help.

  1. Regular owner maintenance checks and stove servicing.

Ensure the stove is cold with no burning embers before undertaking any of the tasks below which are mostly straight forward , once you get used to them.

  • Clean out the ash on a regular basis. (This may seem obvious but it’s often overlooked and the old adage of a little ash in the fire bed for burning wood is often abused.)
  • Regularly check all controls for smooth movement.
  • Burn only seasoned or kiln dried wood that is the correct size for the firebox. Burning wood that is low quality or high in water content will damage your appliance and liner, may cause a chimney fire and is a nasty air pollutant.
  • Check firebricks for cracks monthly.
  • On a 1-3 monthly basis, the baffle plate should be removed and the flue way checked for soot build-up and potential blockage. If you are not confident with removing and replacing the baffle , get your chimney sweep to show you how or do it for you.
  • Clean the glass. If you cannot see the flames then you do not know how well your fire is burning. Remember moderate flaming combustion is what you need.
  • The last part of owner maintenance is planning regular expert maintenance from your local experienced chimney sweep.

2. Chimney sweeping

Regular sweeping of the chimney is imperative to the correct and safe functioning of all solid fuel appliances. Chimney sweeping is a profession that requires a diversified knowledge skill set , the correct equipment and a lot of experience.

It is widely accepted that all chimneys should be swept annually as a minimum. Some chimneys require sweeping twice per year and rarely some even more frequently, depending on use and a variety of other factors. A professional chimney sweep will also provide important advice and confirm with you the required sweeping frequency for your usage , which with a lot of other information will be recorded in his notes too.

3. Solid fuel servicing

Solid fuel servicing is often an unknown variable when people purchase stoves and similar appliances. Whilst it is true that many stoves often last a very long time, it is also true that their internal components often do not. Owners are often surmised to find many of these items are NOT covered by guarantees and are classified as consumables by manufacturers.

The internal stones and grates of an appliance should be designed to survive the rigors of use however they do decay, wear and occasionally break. Repeated opening and closing of doors degrades rope seals which will eventually require replacing. Controls and hinges can become loose or seize with time. Castings and the main body of the stove itself can warp or even crack.

Door Glass can be broken but more often becomes scratched or milky with use and replacing it is not as straightforward as replacing the glass of a house window. The glass used in stoves is often a clear pyro-ceramic which is held in place with heat proof fixings and sealed with a specially sized fiber glass rope. It is specially treated and pre-cut with beveled or smooth edges to prevent early failure

Many owners find it most beneficial to find a professional sweep who also undertakes servicing as this can save time , money and gives peace of mind. Experience is very important when servicing is involved as there are so many appliances , that only time and practice can teach.

Potential risks of maintenance neglect

There are many possible risks to the stove user who avoids or neglects the necessary maintenance and sweeping intervals:

Carbon monoxide poisoning even death
Chimney fire
House fires
Invalidated warranties**
Invalidated home insures**
Shortened appliance lifespan **
Greatly increased running costs
Excessively polluting our air quality
Angry neighbours

*** These risks are very real and significant ***

If you are unsure of what you must do yourself then call your local chimney sweep and ask to have your stove swept , while he is there you can ask for his advice. Although the advice in this post is good general advice please note it is not specific to your particular appliance.

You must take professional advise specific to your particular installation
So Make sure your installer educates you at the time of installation !!! You must also read and follow the guidelines set out by the appliance manufacturer in the instruction manual. You should also be aware of your home insurance company policy regulations and or small print.