What is a Conventional Flue?
Conventional flues are the standard chimneys found in most UK homes. If you have a traditional brick chimney, it is likely a conventional flue. These flues work by allowing air to pass over the top of the chimney, drawing warm air out of the chimney while pulling air from the room through the stove or fire and up into the chimney. As a result, conventional flues need to extend high above the roof line and should terminate in clear air, at least 2.4 meters away from any obstruction or 600mm above the roof ridge.
There are different types of conventional flues, such as Class 1, which are brick-built or clay/concrete lined traditional chimneys that open out into a fireplace. On the other hand, Class 2 chimneys are prefabricated metal flue systems that connect directly to a stove/fire without the need for a fireplace.
All wood-burning, multifuel, and pellet stoves/fires require conventional flues to function properly. Gas stoves and fires can work with multiple flue types, but they are usually designed for either conventional or balanced flues, so it’s important to choose the right version for your home. Depending on the property’s age and the appliance being used, conventional chimneys may require lining.
Advantages:
- Works with a wide range of fuels,
- Traditional look and feel
- Best suited if you already have a chimney in place.
- Works with a variety of fires and stove designs
Disadvantages:
- Needs 4m+ long chimneys/flues in order to work as intended in most cases.
- Requires a flue liner for most modern installations.
- More structural work may be needed if adding a chimney to a property without one.
- Requires a chimney or major building work if you don’t already have one.
- Can lose more heat via ventilation requirements
What is a Balanced Flue?
Balanced flues are applicable only to gas stoves and fires. They consist of two pipes, one inside the other. The inner pipe removes waste gases, while the outer pipe brings in the air required for combustion. These flues, also known as concentric flues, should not be confused with twin-wall flues. Balanced flue appliances are considered “room sealed” because they draw all combustion air from outside and do not require additional air from the room. Consequently, all balanced flue stoves and fires have a glass front or closed door that cannot be opened.
Since hot and cold gases exchange within the same pipe, the outside of balanced flues remains cooler than conventional flues. This feature allows balanced flues to terminate at a lower level, with the only requirement being an external wall where the flue can be directed out the back of the appliance, through the wall, and terminated.
There are specific regulations regarding termination locations, distances, and the amount of free air circulation around the pipe, which may vary between appliances. However, as a general rule, if you have at least 1 meter of free air space around the termination point and it is not directly below a window, you should be compliant (check the appliance’s specifications for further clarification).
Advantages:
- Sealed from the room, improving safety
- Higher efficiency (often 90%+ for gas fires)
- Safer sealed system, no draughts from ventilation grilles
- Flexible placement options – ideal for new builds or homes without chimneys.
- Can run horizontally through a wall or vertically through a roof, doesn’t require a minimum chimney vertical height like conventional flues.
Disadvantages:
- Limited to gas appliances
- Appearance may be more contemporary than traditional
- Must terminate outside in compliance with Building Regulations Document J (minimum distances from windows, doors, and vents) can be complicated to locate correctly depending on your situation.
A common question we receive is whether it is possible to convert a conventional flue chimney into a balanced flue to accommodate a built-in balanced flue fire or freestanding stove. The answer is yes, it is possible, but only with certain products, therefore before making a purchase, ensure that the appliance you are interested in is compatible with these renovation kits.
Chimney Renovation Kits offer a solution to convert conventional flues into balanced flues. These kits provide a concentric pipe off the top of the balanced flue stove/fire into the chimney, where they seal into a special register plate. The inner pipe connects to a chimney liner that runs all the way up the chimney and connects to a special cowl, safely venting the waste gas. This cowl also has lower vents that allow clean air to pass through the void between the outer brick/concrete material of the chimney and the inner liner. The fresh air is drawn into the appliance through the vents at the bottom of the chimney in the special register plate, effectively using the conventional flue as a balanced flue.
