Balanced flues and conventional flues explained

Built-in balanced flue gas fire in a conventional flue chimney

The differences between balanced flues, conventional flues and flueless stoves explained.

Balanced Flues Vs Conventional Flues

Flues play a vital role in removing the combusted gases from your stove of fire; clearly choosing the correct type is important, and understanding why is even more so. Therefore, here is an explanation of the differences between balanced flues, conventional flues and flueless products just for you!

There are a couple of ways of looking at this, first is to determine what you have existing, second is to identify what you can have could you wish to replace or purchase something new. The fuel that you plan to burn can also have impact on your options and should be considered carefully also. The main difference between a balanced flue and a conventional flue, is that a conventional flue utilises an existing chimney and requires an air supply to the room, while a balanced flue is room sealed pulling its air from within the same pipe as the fumes, meaning a balanced flue does not require a chimney and can be placed against any external wall.

Conventional Flues

Called conventional as these are the standard types of chimneys that are installed in most homes throughout the UK. If you have a traditional brick chimney the chances are it is a conventional flue, and works by air passing over the top of the chimney pulling the warm air rising up out of the chimney away. This in turn pulls air from the room through the fire/stove and up into the chimney. Due to this conventional flue chimneys need to rise high above the roof line and should terminate in clear air either 2.4m away from anything (roofline, adjacent building, trees, etc) or atleast 600mm above the ridge of the roof.

There are different types of conventional flue, often called Class 1. brick built or clay/concrete lined traditional chimneys that often open out into a fireplace at the bottom. Class 2. chimneys are typically prefabricated metal flue systems that have been added to a property that does not have a chimney, and function in the same way except they will often connect directly onto a stove/fire rather than opening up into a fireplace.

All wood burning, multifuel and pellet stoves/fires require conventional flues in order to function. Gas stoves and fires can work on multiple flue types however they will be made specifically for one or the other, so ensure you choose the correct version for your home. Conventional chimneys often require lining depending upon the age of the property and the appliance being used, you can find out more about lining chimneys in our dedicated chimney liners and insulation blog post.


Balanced Flues

Only applicable to gas stoves and fires, balanced flues are made up of two pipes, one inside the other. The inner pipe removes the waste gasses, while the outer pipe brings air in that is required for combustion. These balanced flues and often referred to as concentric flues and should not be mistaken with twinwall flues. As these appliances pull all of the combustion air from outside they are classified as room sealed meaning that they do not require any additional air from the room they are placed into, as such all balanced flue stoves and fires  will always have a glass front or closed door that cannot be opened. 

Due to the exchange of hot and cold gasses within the same pipe, the outside of balanced flues do not get as hot as conventional flues, also thanks to this exchange it is not necessary to run balanced flues all the way up and terminate as high as conventional flues. Instead all you need is an external wall, where you can either come direct out the back of the appliance, through the wall and terminate, or rise up, bend 90° through the wall and terminate at a higher level.

There are regulations pertaining to termination locations, distances and the amount of free air that can circulate around the pipe that does vary between appliances, but typically if you are terminating into a space with atleast 1m free air all the way around it and not directly below a window, then you are generally okay (check specific models for further clarification).

So, if you have no chimney in your home, or if you are looking to place a fire in a room that either has no chimney or the chimney is not where you would like to place the fire, then a balanced flue could be the perfect option for you.


Converting a Conventional Flue into a Balanced Flue

One of the questions we often here is that a customer is interested in placing a built-in balanced flue fire or freestanding stove into a conventional flue chimney. Assuming that there is not a conventional flue option available, is it possible to convert a conventional brick chimney into a concentric balanced flue and connect safely into the appliance? – Yes it is possible, but has only been tested on certain products.

Chimney Renovation Kits allow you to convert conventional flues into a balanced flues. These special kits provide a concentric pipe off the top of the stove/fire into the chimney where they will seal into a special register plate. At this stage the inner pipe will be connected to a chimney liner and run all the way up the chimney and connect to a special cowl that will vent the waste gas safely. This special cowl also has vents lower down that let clean air into the chimney passing through the void between the outer brick/concrete material of the chimney and the inner liner. This fresh air is then drawn into the appliance through the vents at the bottom of the chimney in the special register plate, allowing you to use your conventional flue as a balanced flue.

While this option has been available for a number of years it is important to note, that it has not been tested with all products and if you need this solution, you should ensure that the appliance you are looking at is compatible prior to making a purchase.



An alternative to a conventional or balanced flue stove or fire is to choose a flueless model. There are lots of different types of products that do not require flues or chimneys to run, including electric, bio-ethanol and gas. Gas stoves and fires feature a catalytic converter built in to them that burns off all the waste gases, meaning that it does not emit any fumes back into the room and as such requires no flue. The way-off is that outputs tend to be less than 4kW, so are only suitable for either effect only or smaller rooms. Bio-ethanol fires are another flueless product that requires no chimney to be installed as they only produce water vapour back into the room. All flueless products require air vents and minimum room sizes, so check to make sure that your room is suitable for a flueless product prior to purchase.

Hopefully that helps clear up some of the differances between conventional and balanced flues. Got a question? Get in touch in the comments below.

23 thoughts on “Balanced flues and conventional flues explained

  1. We hve a conventional flue but it terminates at about the height of the apex of the roof. We have had the chimney tested and it draws when it is windy but fails when it is high pressure outside with no wind. The chimney is also quite large cross section. Is it possible to fit a liner inside the chimney to improvr matters? Or should we just bore a hole through the chimney, it is on an outside wall, and use a balanced flue.

    1. Hi Alan,

      Thanks for the question. So if you have an existing conventional flue chimney and you can line it with a flexible chimney liner then we would always suggest doing this. We wrote a post about the benefits of lining a conventional flue chimney: which talks about not only lining chimneys but insulating them and the benefits in doing this.

      Typically, conventional flue gas stoves/fires are slightly cheaper to purchase than their balanced flue equivalents. So, if you have an existing chimney then utilising this will often be a less costly way of installing a gas stove/fire as the balanced flue versions are usually more expensive and you need to purchase the specialist pipe to go with them. However, in your situation (which i would suggest is not an uncommon situation to be in) you need to factor in the cost of dropping a liner and potentially insulating it, in order to have a fully functioning chimney. you can see the costs of chimney liners, adaptors and cowls here, and chimney insulation can be found here:

      The other consideration is that depending upon the stove/fire you are looking at, balanced flue appliances are typically room sealed and do not require any additional room ventilation as the fire pulls all the air it needs from within the same pipe. This also means that balanced flue fires are often slightly more efficient than their conventional flue counterparts. Not a huge amount perhaps 5% so, if you work out the costs and they are coming out at a similar amount then this might help you make a decision.

      Last thing to consider is that if you do choose to seal off your conventional flue chimney and place a balanced flue through the chimney you will be altering it beyond its original specification, meaning that you will need to re-alter the chimney at a later date, should you ever wish to go back to the conventional flue chimney.

      Lots of information here, none of which is decisive one way or the other. I do not think there is a right or wrong decision to be made, just what works best for you. If you let us know which model stove/fire you are looking at perhaps we can assist you further and more specifically.

      I hope this helps in the meantime.

      Reece – Fireplace Products

    2. Can I fit External wall insulation if I have a balanced flue? Or would I need to leave a gap around? Can I buy an extension for a select 6 balanced flue? Thanks

      1. Hi Craig,
        As long as the distance to combustible materials rules is followed then you should* be okay. Regarding extending the horizontal flue, this can be tricky, many stove manufacturers only have test data based on the max single length they supply, and therefore have no data as to how well or safe the fire will work if extended further than designed. In some cases they do have that data, and supply you a length of pipe accordingly as they know increasing this will cause problems. You also often find that some of the gas stove manufacturers only offer a terminal length, thus additional lengths are not available, and if you use a third party length of pipe with it, that may also invalidate the warranty or prevent the fire from working correctly/safely. Be very careful if you intend to do something other than what your installer or products manufacture recommends, especially with gas.

  2. Can I put a flueless stove in front of a window in a sunroom – the area directly behind the stove is solid wall but the stove might be an inch and a half above the windowsill. The window is double glazed and the sunroom has a solid roof with a vaulted ceiling of 11 ft.

    Also, how much would it cost to install the stove?

  3. Hi, I have just moved into a property that has an open living flame gas fire fitted to a conventional chimney. I would like to replace this fire with a gas fire stove as I have pets. Do I need a chimney liner? I have seen a conventional flue gas stove that I like.

    1. Hi Teresa,

      It depends on the condition of the chimney and how old the property is. Typically if the stove you are buying has a spigot and can be connected on to a liner, then we would say to do it. Though this is not essential if the chimney is sound, it would certainly be deemed best practice, unless the stove manufactures states that it needs a liner.

  4. We have a blocked up chimney and want to install a gas fire. The gable end of the house is 3 foot stone built. Can we go out the back of the wall rather than trying to reinstate the existing chimney.

    1. Hi Alan,

      Balanced flue gas stoves/fires do not require you to utilise the chimney, depending upon the model you can either go straight out the back and through the wall or up and out. Alternatively look at flueless gas fires and stoves as they do not require any flue, but do require ventilation and minimum room sizes. Hope it helps, Reece

  5. Hi, I have a balanced glue fire in my lounge which we’d like to update to a more modern gas fire. Is this possible? Could we use a multi flue gas fire?

    1. Hi Rav,

      Multi-flue gas liner is typically used for different types of gas burners based on their outputs. For example many gas burners have a gas input of just under 7kW these need to be run on a 7″ flue if it is an open fire. If the output is lower then this can often be run on a smaller diameter such as a 5″ flue. Balanced flue products are more designed for homes without a chimney as you can vent the pipe up and out through the wall. As it is pulling both fresh air in and waste gas out of one pipe you do not need a conventional chimney and therefore a liner. So if you are looking to replace your balanced flue gas fire with something more modern, if the new appliance is a balanced flue products then you should be fine, as you have had a balanced flue fire in that location previously. if the new fire is conventional flue then it will probably require a little more planning and best to get a local GAS SAFE engineer to come and take a look for you. Hope it helps, Reece

    1. Hi Steven,

      Gazco used to sell power flues for their conventional flue gas stoves. I believe they no longer make them due to lack of popularity so yes you should be able to do this, if you can find someone who has one still. I have checked our stock and we do not im afraid. Thanks Reece

  6. We have just moved into a bungalow which has a balanced flue on the outside wall. The internal wall has no fireplace but we would like to put one in. We have been told that we cannot use the existing flue as it is on the neighbouring properties driveway as part of the property boundary and it needs to be around 1 meter clearance of the boundary. Is this correct?

    1. Hi Jayne, thanks for the message. Im not 100% sure about the 1m regulation but it does sound about right. Keep in mind these rules can change from time to time, so its possible that it was fine when it was installed but does not conform now. Have you had a Gas Safe engineer come and take a look at it yet? They will be able to advise the specific regulations to your property and advise on installation costs etc. Thanks Reece

  7. We need to have a balanced flue for our gas stove but they look so ugly from the outside. Is there any way to hide them? Why can’t it go through the roof?

    1. Hi Jane,
      Good News they can go through the roof! Well, it depends on the model, but there are gas stoves available that have a top exit and that can run vertically up through the ceiling and out of the roof. There is sometimes a maximum distance rule, but it depends on the product. Balanced flue products typically offer a rear exit as it negates the need to run a vertical chimney, and is the only fuel type to offer this. The terminals themselves are not terrible looking (again depending upon the product) its often the cage that has to go around them that is the un-attractive element. Cages are required as a safety precaution on any terminal that exits the wall lower than 2m off the floor externally. The other option you have is whats called an “up and out” kit whereby you can rise up vertically 1m, 1.5m then 90° and go through the wall and terminate higher up the wall. This can often be done with a much smaller terminal than the horizontal terminal, and if it is above 2m off the floor outside there is no need for a guard. So that might be another option for you, and the pipe that is seen inside is sometimes available in a black colour to match the stove and gives a more authentic woodburner look to the install. Hope that helps, Reece

  8. Looking at contemporary gas stove and ideally wanted it to sit in the corner of the room.

    I’ve been told the balanced flue must be 600mm from the corner but this means it’ll not be in the corner.

    Any thoughts on what I could do and which of your stoves you’d recommend.

    The corner of the room is block and the outside is external on back and side. Read somewhere that fanned draught can be 300mm but can’t see that’s an option with a gas stove?

    What’s the reason for this distance and is it 600mm from the corner outside my house or needs to be 600mm inside?


    1. Hi Stephen, thanks for the question. So, just been looking upon this a little bit more. First of its 600mm externally, not internally and I have seen some products that say a minimum of 500mm rather than 600 (Wanders Tali for example; It seems as though this is primarily to do with airflow around the flue exit, as keep in mind both the waste gases are expelled and fresh air is intaken at the flue exit, so if it is too close to an internal corner than there is likely insufficient airflow, and on an external corner too much airflow. I think there is also a safety aspect to the flue protruding out of the wall on an external corner to someone walking round the corner and depending upon the height of the exit walking straight into it. Keep in mind you should have a guard on all balanced flues existing below 2m externally to the ground. I suspect though if you have a cavity wall, and placed a stove such as the Tali into the corner facing outwards and keeping to the minimum air gap spacing the stove needs around it (usually 150-200mm) then by the time the flue comes up and goes out through the wall it should be atleast 500mm away from the external corner anyway. Infact we just ran the numbers on the Tali and we calculate based on a 230mm thick wall, and a 150mm gap around the stove the centre of your flue will be 610mm away from the external corner. We hope that helps if anyone needs any help in calculating flue sizes, distances or runs then please contact our sales team or 01268 200139

    1. Hi Kerry, Do you mean multi-flue or multi-fuel? Multi flue fires typically are designed for conventional flues (not balanced flues) and allow them to be installed on multiple types of conventional flues. Multi fuel, are woodburning stoves that can also burn briquettes, smokeless coal and sometimes peat. For further assistance on choosing the right new fire, best speaking to our sales team: or call on 012168 200139

  9. Hi I’m thinking of purchasing a balanced flue gas fire but I’ve still got chimney breast in my room.Can I still fit the balanced flue fire and get outlets so it can be fitted on chimney breast also my outlet is on footpath
    So outlet would be at 2meters so it doesn’t interfere with footpath.
    Is this possible to do.

    1. Thanks for the question. So, you can often convert an existing conventional flue into a balanced flue with a chimney renovation kit (not available from all manufacturers, so check the brand has the option before you buy). They are not cheap, but do same the hassle of attempting to remove your existing chimney or trying to fit rigid pipe, which is often next to impossible in an existing chimney. Regarding outlets, again depending upon the product it is possible to get warm air ducts off of a gas fire, so you can vent some of the heat that is often lost in the chimney back into the room. It is important to remember that this is just hot air ducted in a pipe back into the room, and nothing to do with the flue. Regarding outside providing you terminate 2m above the floor level you do not need a cage, that being said it does act as a good visual indicator for people to see the chimney pipe, so it might be worth fitting one. You can speak to a member of our sales team who will be able to help you more specifically with your enquiry if you like. or 01268 200139, Hope that helps.

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