Stove Terminology Glossary
Below you will find explanations of some common terms used in connection with stove and flues - if you are unsure of anything here please feel free to call us for any further help or advice:
Air Vent - this term can refer to 2 different things - primarily refering to the vents on the stove that allow air into the firebox for combustion. On most stoves there will be at least a Primary vent and Secondary vent, plus sometimes a Tertiary (third) vent for extra-clean burning. A vent can also refer to the Room Vent for allowing clean air into the room to ensure there is sufficient air for the stove (see Room Vent below).
Air Wash - this is a feature of most modern stoves. Air (usually from the Secondary vent on the stove) is deflected to flow down behind the glass to help prevent soot sticking on the glass thereby keeping it much clearer. We suggest the Secondary vent is always at least partly open. Closing it completely will result in the glass blackening up more quickly.
Aperture - this refers to the opening in the wall / chimney breast into which a stove or fireplace insert is fitted. Measure the height, width and depth of your aperture to see if your chosen stove model will fit inside. Also, see Builders Opening.
Baffle Plate - a plate that sits in the top of the firebox, usually made from steel or cast iron. It's purpose is to help keep heat in the firebox, reducing heat going up the flue / chimney. Combustion gases and smoke have to flow around the plate before exiting the stove - this allows more time and higher heat for more thorough combustion, resulting in improved efficiency and cleaner burning. All modern stoves will have some sort of baffle plate. Often they are loosely fitted to allow easy removal - so you can sweep the flue directly through the stove. On some of the very clean-burning stoves the baffle is either fixed in place or may be difficult to remove - on those models you should have an access hatch/door in the first section of flue pipe above the stove to allow cleaning of the flueways.
Builder's Opening - this is the hole in the wall / chimney breast that is left open by the builder when the wall or house is originally built. Into this Opening can be fitted a fireplace back / chair-brick for an open fire, or left clear for a stove - if a stove is installed the inside faces of the Opening may be rendered with cement or lined with a suitable non-combustible board.
Building Control - The role of checking that Building Regulations are being complied with falls to Building Control Bodies. There are two types - a Local Authority Building Control service and a private sector Approved Inspector Building Control service. Customers are free to choose which type of Building Control Body they use on their project. The Local Authority i.e. your local Council is the most common method although the use of private Building Inspectors is becoming more widespread. Note: if your stove / flue system is installeld by a HETAS registered installer there is no requirement for you to also go through Building Control as the HETAS installer is allowed to self-certify the installation.
Building Regulations - Any work that affects an existing chimney (including installation of a stove or flue liner) or creates a new chimney is considered building work and so comes under the Building Regulations. The actual Building Regulations are a simple set of short paragraphs essentially stating that the installation must be safe and suitable for purpose. If any work does come under the Building Regulations it is a legal requirement to comply with it. How you achieve this and comply with the Regulations is often open to interpretation of the guidelines. The Government issue an Approved Document which contains practical guidance on ways of complying with the Requirements of the Building Regulations. Document J is in itself not the law, but essentially a detailed set of recommendations showing how combustion appliances and their associated flues can be safely fitted. If you are self-installing (or you use a builder etc.) and are having the installation signed-off by the Building Inspector, the Inspector will look at the guidelines in Document J to check compliance. Note: if you do not follow all of the guidelines it does not necessarily mean you have not complied with the Regulations - it just means you have to satisfy the Inspector that what you have done is safe and suitable. Note: if the installation is done by a HETAS installer they will usually work to their own set of HETAS guidelines - this is typically based on Document J but may also go further i.e. be more stringent. Typically a HETAS installer will of course only be prepared to put his/her name to an installation if they are fully confident it is compliant with the Building Regulations and safe.
Note: certain installations e.g. for stoves installed into sheds / cabins / workshops etc may not be subject to Building Regulations - in these cases we suggest it is up to the person fitting it to ensure it is safe and suitable for use.
Carbon Monoxide Alarm - Carbon Monoxide (CO) is a poisonous gas that is a by-product of burning carbon-based fuels (essentially wood, and fossil-fuels such as coal, oil or gas). When a fuel is burned in the presence of enough oxygen Carbon Dioxide (harmless) is formed. When there is a lack of oxygen in the fire there is incomplete combustion of the fuel resulting in the formation of Carbon Monoxide. It's toxicity and danger to humans come from the fact that CO binds more easily to Haemoglobin (the molecule in red blood cells that carries Oxygen around the body) than it does to Oxygen. As the level of CO in a room increases and is breathed in the amount of oxygen getting to the brain and muscles is reduced. CO is colourless and odourless so difficult to detect. This is why a Carbon Monoxide Alarm / Detector must be fitted in any room containing a solid-fuel appliance e.g. wood burning stove. Carbon Monoxide poisoning is rare but it is always better to be safe than sorry!
Cast Iron - the traditional material used to build stoves / woodburners. Molten iron is poured into shaped moulds to form the various parts of the stove e.g. sides, base, top, door etc. The individual parts are hand-finished and then bolted together from the inside to form the stove. The alternative to this is the use of steel to make the stoves (see Steel below). Cast Iron has the advantage over steel of retaining heat better, thereby ensuring the stove is still radiating heat to the room even when the fire inside has died down. In practice, in most normal homes the advantages/disadvantages of cast iron vs steel will be minimal. The choice of stove material is really more of a cosmetic choice. Cast Iron stoves can have more decorative (traditional) patterns or designs. Steel stoves tend to have flatter surfaces and are often considered more modern / contemporary in appearance. Unfortunately there is a bit of a myth often fed to potential customers about the likelyhood of cast iron stoves cracking as they are more brittle than a steel stove. We sell thousands of cast iron stoves each year and have seen typically 1 in 5000 stoves develop a crack and even then that was due to improper use. Some manufacturers only make cast iron stoves and so promote them as the best, others only make steel stoves so likewise only promote their chosen material. We do stoves made fully from cast iron, fully from steel, and also hybrid stoves with thick steel bodies and cast iron doors and inner components.
Chimney - This is the structure that provides ventilation for the combustion products / gases / smoke created by a fuel burning appliance. Typically the chimney is constructed from brickwork and rises from the fireplace up through the house and above the roof. A chimney may be internal or external (on the outside of the house). Houses without an existing brick chimney can be fitted with a factory-made metal chimney (see Twinwall Flue below). Note: the terms Chimney and Flue are often used to mean the same thing, however, technically they do have a different meaning (see Flue below).
Clean Air Act - a law that prohibits emissions of smoke within smoke control areas, unless using an exempted appliance or an authorised fuel. See DEFRA below.
Collar - a steel or cast iron ring that bolts to the top or rear outlet of a stove, into which sits the first section of flue pipe. On most makes and models of stove the collar comes loose inside the stove and the customer or installer secures it into place. The collar is usually a bit larger then the flue pipe so the small gap is sealed with fire cement (and fire rope if required). Note: in the UK the flue pipe should fit INSIDE the collar, however, on some European stoves the collar is the same size or smaller than the flue pipe - in these cases you can fit a Continental Adaptor to enable you to use standard UK size flue pipe. On stoves with both top and rear outlets the outlet not in use is sealed with a Blanking Plate.
Consumable Parts - many of the components that make up the stove will have a certain lifespan dependent on the amount of use they get and the temperatures involved. For example, the Grate and inner lining plates inside the firebox are designed to be easily replaceable. Many people never need to change these parts whereas other people may need to replace the grate every few years. If burning a lot of high temperature coal or if you have an over-drawing chimney it will tend to shorten the life of these parts. Other replaceable parts are the Baffle Plate and rope seals around the door. If the glass in the door is broken it can easily be replaced. Manufacturers will generally exclude all of these items from any guarantee as they have no control over how a customer uses (and potentially abuses) the stove. Stove guarantees will generally cover the main body of the stove against manufacturing defects.
Damper - a movable flap in the flue that can be opened/closed to allow more or less air up the chimney thereby allowing control e.g. to slow the rate of burning down, to keep the stove going over-night etc. Some old stoves had the damper built in on the top of the stove. Modern stoves being much more efficient (i.e. allowing less heat up the flue) do not normally need a damper built in. If you know you have a strong chimney draw, or particularly want to be able to slow the fire down a lot, then you can buy a damper unit to form the first section of flue pipe.
DEFRA - this is a term often mentioned in relation to stoves/woodburners. The Department for Environment, Food & Rural Affairs is responsible for, among other things, environmental protection and control. This includes ensuring compliance with the Clean Air Act (see above). Stoves are often described as DEFRA Approved (or DEFRA Exempt - meaning the same thing) if they have been tested and proved to have low smoke emmisions when burning wood. Most large towns and cities will be Smoke Control Areas - if you live in these areas and want to burn wood your stove must be a DEFRA Approved / Exempted model. When looking for a stove either in a showroom or on the internet they will always clearly state whether or not they are DEFRA Approved. If it doesn't say DEFRA then it is most likely not. Note: a non-DEFRA stove can legally be used in a smoke control area but only if burning smokeless fuel.
Document J - The Government issue an Approved Document which contains practical guidance on ways of complying with the Requirements of the Building Regulations. Document J is in itself not the law, but essentially a detailed set of recommendations showing how combustion appliances and their associated flues can be safely fitted. See Building Regulations above.
Draught / Draw - For a Wood burner / Multi-fuel Stove to work safely and correctly the combustion products / smoke must exit up the flue and at the same time clean air must enter the firebox to feed the fire. This movement of smoke and air is caused by the flue / chimney draught. The draught or draw is caused by the difference in air pressure between the bottom end (i.e. the stove) and the top of the chimney. When the stove is cold e.g. when you first try to light the fire, the main thing that affects the draw will be the height of the chimney - the pressure at the top of a tall chimney will be lower than the pressure at the top of a short chimney (e.g. compare a 3-story house with a bungalow), therefore the Pressure Difference between top and bottom will be greater. This is known as the Initial Draw. It means that it is usually easier to light a fire if there is a tall chimney, and can be more difficult when the chimney is short or has bends and offsets (as these weaken the draw too). As well as the natural pressure difference due to height the air inside the house will tend to be warmer (and less dense) than the air on the outside of the house at the same level, this less dense air will naturally start to rise up the chimney and cooler dense air from the outside will move into the house. This is why it is generally easier to light a fire on a cold day, and can be difficult to light a fire on a hot summer day. Once a fire is established and the flue begins to warm up any lack of height in the chimney will become less of an issue. To improve the draw on any flue/chimney it is important to get the flue warmed up quickly and to maintain a good temperature in the flue. On an old property this can be achieved by relining the chimney with a smaller diameter flue liner e.g. a 6" diameter stainless steel liner will stay a lot warmer (therefore improving draw, and efficiency, and cleanliness) than the original 9" square brick chimney. The liner can also be insulated to further improve things. The majority of performance issues with stoves can be attributed to poor draw . The same stove can work quite differently in a different house because of different chimney heights, diameters, air temperatures etc. Note: a very strong draw is not necessarily a good thing either - if a house has a very tall chimney the draw will be good for initially starting the fire but it may mean the stove is difficult to slow down, especially if you want to burn slowly through the evening, as the chimney will keep pulling air through the stove even with the air vents in the closed positions. Note: this is more noticeable with DEFRA Approved stoves as these are not legally allowed to shut right down anyway - they must allow a certain amount of air in at all times to ensure clean burning.
Efficiency - A measure of how much energy is NOT lost up the flue e.g. if 20% of the energy released from burning the fuel goes up the flue then the appliance is certified as 80% Efficient. Some stoves have very high rated efficiencies - this is not necessarily an advantage for everyone as the higher the efficiency of the stove the taller the chimney needs to be to make it work. A certain amount of heat needs to go up the flue to make the stove work properly. If you have a short chimney or suffer from a poor natural chimney draught then it will actually be easier for you to light a stove with a lower efficiency. Don't be too concerned when making a decision on stove model by the efficiencies - a stove rated as 75% or 80% efficient will have little noticeable difference when in use in a normal house. All stoves sold in the UK must be tested and certified to meet minimum European efficiency levels anyway. Also note: an Inset / Insert / Cassette stove may have the same rated efficiency as a free-standing model e.g. 80% but that does not mean it will heat the room quite as effectively. The 80% measure just means 20% of the heat went up the flue, it does not mean (in the case of an Inset stove) that 80% of the heat goes into the room, as some heat will be "lost" from the back of the stove into the chimney void and brickwork of the fireplace.
Firebox - The chamber inside a stove where the actual combustion (burning of fuel) takes place.
Fire Bricks - In most stoves the inside walls of the firebox are lined with loose-fitting panels usually called firebricks. These serve 2 purposes - firstly they help to keep heat in the firebox leading to higher efficiencies and cleaner combustion, and secondly to protect the outer walls of the stove from the direct heat of the flames. Traditionally the firebricks were made from Refractory Clay, but now many stoves (e.s. the Saltfire ST range) are lined with Vermiculite boards instead. Some stoves (most of the Saltfire Traditional range) are lined with cast iron inner plates.
Fire Cement - A putty-like substance used to seal the joints between vitreous enamel flue pipes and also where the flue pipe connects to the stove. It can be applied by hand and will harden when the stove is first used. Take care to wipe off any excess before it has dried.
Fire Rope - A heat-resistant rope-like material sometimes called ceramic rope. It is used in virtually all stoves to make a seal at various edges/joins in the stove. e.g. most stoves will have a fire rope around the edge of the door to make a seal when it is closed. Most will also use a rope to seal between the glass and the door. Cast iron stoves will have a rope to seal between each individual part of the stove body e.g. sides, base, top etc.
Flue - The flue is the actual passageway / duct that the smoke and gases travel through. The flue is contained within the Chimney (see Chimney above). Technically the pipe itself is not the flue, the flue or flueway is the hole inside the pipe. In practice many people (including professionals) often use the term flue to refer to the pipework.
Flue Diameter - Simply the diameter of the flue, typically 5" for smaller and very clean-burning appliances, or 6" for most larger stoves. Note: many small stoves have a 5" outlet on the stove (so will use 5" vitreous flue pipe) but you must then step up to a 6" flue inside the chimney e.g. if connected to a flexible flue liner or twinwall flue system. Some older stove models (or new but very large models) may still need a 7" flue although these are quite rare now. Note: an open-fires usually needs a minimum of an 8" diameter flue. Larger fires/stoves need larger flues as they simply have a greater volume of flue gases that need to exit the fire. Many of the DEFRA Approved stoves can use a 5" liner right to the top as they have been tested to show they produce very little smoke. Flue diameters are still typically described in imperial (inches) in the UK even though the other measurements such as height are usually described in metric (m or mm).
Flue Liner / Flexible Liner - A pipe usually made from 2 layers of stainless steel that is used to line or re-line an existing chimney. It comes as a coil cut to your specified length e.g. 8m or 9m typical for a 2-storey house or 5m or 6m for a bungalow. Lining an older chimney will generally improve the performance of the stove and ensure a safe system. It is not a legal requirement to re-line the chimney if the existing chimney is in good safe working order and not leaking, however, we would always recommend it especially on an older property, and most professional installers will insist on lining the chimney if you want them to fit a stove.
Flue Pipe - This usually refers to the pipe that connects the stove to the chimney so also known as Connecting Pipe. Usually made from steel and coated with vitreous enamel so can be called Enamel Pipe, Vitreous Pipe or simply Vit. Some connecting pipes are made from stainless steel, although this is not very common in the UK. The Flue Pipe most commonly joins to the top of the stove (via the Collar, see above), and is sealed with Fire Cement, although many stoves also have rear flue outlets, to which a 90° bend or Tee piece is fitted before the flue rises vertically.
Free-Standing Stove - This simply means a stove with legs or a base on which it stands. A free-standing stove can fit inside a fireplace opening with a small gap around it or can stand in the open e.g. in a room with no fireplace. The other type of stove design is an Inset or Insert stove (see Inset Stove below).
Front Bars / Log Retainer - Found in most types of stove - some form of bar that fits across the front of the firebox at the bottom to prevent logs from falling out of the stove when the door is opened. The bars are often removable.
Grate - At the bottom of the firebox in a multi-fuel stove. The grate forms the base upon which the fuel is burned. The grate will have a series of holes or slots cut into it to allow air to get to the fuel from underneath - important when burning coal. Grates are usually made from cast iron. They are designed to be a user replaceable part (consumable). Not usually covered under a manufacturer's guarantee as their typical lifespan will depend on how a stove is used, type of fuel and chimney strength etc. Use of unsuitable fuels e.g. petro-coke, or an over-drawing chimney will shorten the life of a grate.
Hearth - This is the floor or base of a fireplace, onto which sits your stove. A hearth is made from a solid non-combustible material. There are 2 types of hearth to be aware of: the Constructional Hearth - this is usually a concrete slab at least 125mm thick and extending out in front and to the sides of the fireplace. Most large stoves in the UK require a constructional hearth. The second type is the Superimposed Hearth (or Decorative Hearth). This is a thinner material and can be made of e.g. slate, stone, glass, ceramic tiles etc. Many of our stoves have been tested to show the hearth temperature is not raised to more than 100°C. This means they do not require a Constructional Hearth and can sit on a decorative hearth of minimum 12mm thickness. This hearth itself can sit directly onto a wooden floor. These stoves are usually described as "suitable for 12mm hearth". All of the Ekol range, including the large models, are suitable for a 12mm hearth.
Heat Output - A measure of the amount of energy emitted from a stove. In simple terms the amount of heat you get from the stove depends on the amount of fuel you burn. When comparing different makes and models of stove the heat output measure is not always the important thing to look at - as a manufacturer can specify what output they want to achieve when a stove goes for it's official testing. A better way to compare different models is to look at the firebox size. If 2 stoves have the same size firebox and similar efficiency they will be capable of burning through the same amount of fuel therefore having the same heating effect to the room regardless of the "official" stated heat output. See Efficiency above and kW below.
HETAS - HETAS is the official body recognised by Government to approve biomass and solid fuel heating appliances, fuels and services, including the registration of competent installers and servicing businesses. Primarily they provide training for installers - if your installer is HETAS registered they are allowed to certify the installation, so you do not have to go through the local Building Control process. You can find a local HETAS installer here: http://www.hetas.co.uk/find-installer/ .
Hybrid Stove - Our Ekol range of stoves are made from a thick steel body but have a cast iron door and cast iron inner components including a high-chromium cast iron grate for longer life-span. The use of different materials optimises the performance of these stoves ensuring the best experience for the customer, making wood-burning safe, easy and clean.
Inset Stove - An Inset (or Insert) Stove is designed to fit into an existing or new hole/opening in a wall or fireplace. The face of the stove usually sits flush or slightly proud of the wall. These type of stoves can give a neat finish, especially if you don't want the stove to take up space in the room. Some Inset stoves are designed to sit on the hearth while some can fit in a hole further up off the ground. Some Inset models have an outer "shell" or second layer on the back of the stove body to minimise heat loss into the chimney and allow convection of warm air into the room through vents or slots on the face of the stove - these are sometimes referred to as Cassette stoves.
Insulated Flue - Usually referring to the Twin-wall (see below) Insulated Flue Pipes used to form a chimney in a modern house where there is no brick chimney, or in an older property where the original chimney has been removed. Can also refer to the practice of insulating (either with a special blanket wrapping or loose fill material) around a flexible chimney liner.
kW - The standard unit for the measurement of power is the watt. kW means 1000 watts. Commonly used to measure the power output of heaters. A small electric fire would normally have an output of 1kW. A small wood-burning stove may have a rated output of 5kW - the actual output you get in use will depend on the amount and quality of fuel you are burning. See Heat Output above.
Log Size - Often given in the description of a stove model. The length of log that can reasonably be fitted into the stove. e.g. a small stove may take a 10" (250mm) long log. If you are not restricted on the width of the stove e.g. when the stove is free-standing in the room, then it can be useful to have a wider stove as larger logs can be burned, meaning less chopping of the wood, and less frequent re-fueling of the stove.
Multi-fuel - If a stove is described as multi-fuel it means it can safely burn fuels other than wood logs. Typically the other fuels will include natural smokeless coal (e.g. Anthracite) or manufactured coal products, but may also include fuels like peat. Some solid fuels e.g. petroleum based Coke (Pet Coke) or coal designed only for use on open fires should not be used in any stove - it will potentially damage the grate and inner components of the stove. Multi-fuel stoves always have a raised grate to allow air from below and for the ash to fall through (see Grate above). Contrast with Woodburner below.
Primary Vent - All wood burners and multi fuel stoves will have at least one vent through which air enters the stove - there is normally a vent at the bottom of the door allowing air into the lower part of the firebox - this is the Primary Vent. If burning wood then you may typically open the Primary Vent when first lighting the stove - letting in plenty of air to the firebox to get the fire going. Once the stove starts to warm up you would normally then close this vent and use the Secondary or Tertiary Vents (see below) for control. If burning coal you will probably have the primary vent at least partly open all of the time to ensure good air supply to the base of the coals.
Register Plate - This is an essential component when installing a stove into a fireplace with traditional masonry chimney above. The register plate is usually made from steel (but can in theory be made from a suitable non-combustible board material). The Register plate will have a hole cut in it through witch the flue pipe passes. The Register Plate seals off the chimney from the room so that air can only be drawn directly through the stove and into the flue / chimney. This is important because the draw on the stove is created by the chimney - if there was no register plate air would be "pulled" from the room around the outside of the stove and into the chimney, little air would actually enter the stove so starting and maintaining a fire would be very difficult. The Register plate also serves some secondary purposes too - it helps prevent excess heat loss from the room into the chimney void and also protects the stove and room from any dirt or debris that may fall down the chimney. If you are using a flexible flue liner to re-line the chimney then the primary function of the register plate (to seal off the chimney) is not really significant as all of the draw will be through the flue liner which is then connected directly to the stove flue pipe. However, it is still normal practice to fit a Register plate in this case as it will still serve the secondary purposes of heat retention etc. Also, if you want to insulate the liner e.g. with Vermiculite, the Register plate will be needed to stop the insulation falling straight down into the room. Technically in the case of an installation with a liner the Register plate can be called a Closure Plate - to most people it means the same thing though and is actually the same item, although used for a different purpose.
Riddler - Many multifuel stoves have a Riddling Mechanism or Riddler - this means that part of the grate rotates or shakes to allow the ash to fall through the grate into the ash pan below. The riddler is usually operated by a know on the front or side of the stove which is pulled/pushed.
Room Vent - This is required for many stoves depending on the kW output and age of the house. Stoves need a constant supply of air to feed the fire to allow for thorough combustion of the fuel. In most houses you can install a stove upto and including 5kW output without the need for a room vent. The air requirement for a larger stove is of course greater than for a small one so in most properties any stove with more than 5kW output will normally require a vent in the same room (note: for new-build properties, which are much more air-tight than older buildings, a vent is almost always now required even for the smallest stoves).
Secondary Vent - A second air inlet usually located above the door - this lets air into the top of the firebox which is much more efficient for burning wood. The secondary air is also usually deflected by a channel plate so it flows down behind the glass helping to keep it clear of soot deposits (see Airwash above).
Slumbering - This refers to slowing down the rate at which the fuel is burned so you can keep the fire going for a long period. Shutting off all of the vents on a stove will restrict the amount of air going into the firebox and slow down the fire. People may want to keep a fire going over-night so they can simply add some new logs first thing in the morning and get the fire back up to temperature quickly. This is easier to achieve if you have a relatively short chimney height. It is more difficult to slumber a stove if you have a tall chimney (the draw will be stronger and tend to keep pulling air through the stove - see Draught / Draw above). Also it may be very difficult to slumber a clean-burning or DEFRA stove as the vents on these are not allowed to shut down completely. If you know you want to try to burn over-night it can be worth fitting a damper in the flue during installation as this will give another layer of control - see Damper above.
Smoke Control Zone - A designated geographical area inside which the burning of unauthorised fuels (e.g. wood) is not permitted in a house unless in an Execpted Appliance (see DEFRA and Clean Air Act above). Most large cities will be Smoke Control Zones, most rural areas away from large towns will not be. If unsure just call your local council and ask if you are in a smoke control area. More information can be found on the government website here: www.gov.uk/smoke-control-area-rules If you are in a smoke control area make sure you look for a stove described as DEFRA Approved or Exempted. All of the Ekol range and the Saltfire ST range are DEFRA exempt as they are designed from the start to be very clean burning.
Spigot - See Collar above.
Stainless Steel Grades - Flexible flue liners come in 2 main types - either 316 Grade or 904 Grade. The 904 Grade is quite a bit more expensive than the 316. The difference is in the mixture of different metals in the stainless steel. 904 Grade stainless contains a higher proportion of expensive elements such as Molybdenum and Nickel, which significantly increase the cost of making the liner. The actual quality of construction is not any different - 904 liner may be made on the same machine in the same factory as the 316 liner. Note: all solid fuel / wood / multifuel liners (i.e. all of the ones we are interested in) are made from 2 layers of stainless steel folded over. The 316 liner is either made from 2 separate strips of 316 steel or may be made from a single strip that is folded back on itself to form 2 layers. The 904 grade liners are typically 904 steel on both layers if they are formed from a single strip folded over, or can be 904 grade on the inside and 316 grade on the outside if made from 2 separate strips (it is the inside of the flue that is subject to potential corrosion from soot/tar etc). There are good quality and poor quality liners available in both grades - buy from a reputable firm. We only sell high quality liners and supply many other shops and professional installers all around the country. The potential advantage of the 904 grade liner is that this type of steel is more resistant to acid corrosion which may result from burning coal and/or having slow slumbering fires (e.g. if you burn over-night). Also the 904 liner typically has a guarantee period twice that of the 316 (part of what you are paying for is the piece of mind that the longer guarantee confers). Our advice is that a good quality 316 liner is perfectly suitable for most people in most situations - most people only burn wood (even on a multi-fuel stove) and usually have a fire going for a few hours during the evening. If you know you want to mainly burn coal or want to have slow slumbering fires then the 904 is proabbly worth the extra cost. If you have the budget to spend more and want the piece of mind of a very long guarantee then consider the 904. We sell the excellent quality Duraflue 904 liner which has a 30 Year Guarantee.
Steel - The alternative material to cast iron (see Cast Iron above) for constructing a stove. Steel stoves are made from large sheets of steel which are typically laser cut, folded, and welded to form the body of the stove. This is generally less labour-intensive than making a cast iron stove. The steel can also be cut or folded into more modern shapes and designs. Steel stoves heat up quickly, but also loose any stored heat quicker than a cast iron stove. Regardless of the materials, stoves of similar physical size will generally do a very similar job in terms of heating a room so the choice of one over another is mainly cosmetic.
Sweeping Door - A small door or hatch fitted into a length of the enamel flue pipe. This door can be removed (usually held in place by 2 screws) to allow the flue to be swept by the chimney sweep. Usually required if you cannot easily access the flue through the stove.
Tertiary Vent - A third air inlet found on many clean burning (usually DEFRA Approved) stoves. This vent is often at the back of the stove (but may be controlled by a lever on the front or underneath) and lets air in from behind the firebox to ensure a very thorough and complete combustion of the fuel. This air is also often pre-warmed before entering the firebox further helping things.
Twinwall Flue - This is a system of pipes used to form a chimney when there is no existing masonry chimney that can be used. The twinwall pipes are made from stainless steel with an insulating material (such as Rockwall) between the inner and outer layers. It is designed to keep the heat inside the flue, so the outside of the pipe can pass safely near (minimum 60mm gap) to combustible materials e.g. wood. Different brands of twinwall flue pipes are not compatible with each other due to differences in the exact diameters and profiles at the ends of the pipes. Our twinwall system is of a very high qaulity and is tested for use at 600°C (most other brands are only tested for use up to 450°C). Twinwall pipes simply push together and a locking band is then tightened around the joint. No sealants are required.
Vitreous Enamel - Refers to the most common type of pipe used to connect the stove to the chimney. See Flue Pipe above.
Woodburner - A closed heating appliance designed to burn wood logs. Generally described as a stove. Unless stated or described as multi-fuel (see above) then it is for wood only, not coal. Woodburning stoves have a flat base (without a grate) on which the logs are burned.