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.

 

Flueless

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.

3 comments

  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: https://www.fireplaceproducts.co.uk/blog/insulating-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. https://www.fireplaceproducts.co.uk/5inch-chimney-liner/ you can see the costs of chimney liners, adaptors and cowls here, and chimney insulation can be found here: https://www.fireplaceproducts.co.uk/chimney-insulation/

      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 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?

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