If you think you might want to install a wood-burning stove or a fireplace, or maybe you want to make use of an existing chimney (or have one built) then you need to understand the main differences between a chimney and a flue.

Chimney or flueAt flue-pipes.com, we've been helping people like you for over a decade to plan and install these cozy home heating solutions with the minimum of fuss and maximum satisfaction. Let us help you take into consideration the safety issues, the legal requirements, and of course, the budget when dealing with getting the hot air and waste efficiently up and out of your home so that you can enjoy all the benefits of this cozy and enjoyable form of heating.


The Basic Difference Between A Chimney And a Flue

Chimneys and flues are so often confused, so this is the bit most homeowners pay attention to.

A chimney is a vertical structure that protrudes above the roofline of a building, typically made of brick, stone, or metal, and designed to provide a path for the exhaust gases produced by things such as wood-burning fires to escape into the atmosphere. They can be single or multi-flue, with each flue serving a separate appliance, such as a fireplace, stove, or boiler.

Flues or "chimney flues" are ducts or pipes that carry exhaust gases from the appliance to the chimney or outside of the building. Flues can be made of various materials such as stainless steel, aluminium, or ceramic and can be either rigid or flexible. There are two types of flues commonly used in gas appliances: balanced flues and conventional flues. A balanced flue system is designed to draw in air from outside the building to exhaust the waste gases through the flue. Conventional flues draw in air for combustion from inside the building and exhaust the gases through the chimney.


The terms: Chimney v Chimney flue

In general, the terms "flue" and "chimney flue" can be used interchangeably to some extent, but they are not completely synonymous. A flue refers to a duct or pipe that carries exhaust gases, while a chimney flue refers specifically to the pipe or duct within a chimney that is used to exhaust gases from combustion. In other words, a chimney flue is a part of the chimney system, whereas a flue can be part of a chimney system or another type of venting system.

The main difference

The main difference between a chimney and a flue is that a chimney is a completely vertical structure, while a flue is a part of the chimney system. It is a crucial component of the outflow system as it directs the harmful combustion gases outside your building. Chimneys can have multiple flues to deal with multiple appliances, whereas a flue usually only serves one appliance. In addition, they are usually constructed with materials that can withstand the high temperatures produced by combustion. Flues can be made from a variety of materials depending on the application. They both play an important role in maintaining the safety and efficiency of heating appliances in homes and commercial buildings.‍


The different types of flue

There are many flues available in several different types of material and they can’t all be used for the same types of fuel. If you are unsure about which fuel to use, talk to your supplier who should have everything you need to know.

So now, let's get clear on the different types on offer, so you can make decisions and understand what is best in your case.


Masonry Parged Flues

These are mostly in houses built before 1966- usually rectangular or square flue and lined with mortar. If you have one of these, then we really recommend you get it checked out before installing anything as they can be hazardous or in need of work. You don't want to end up with the risk of excessive-high heat or a chimney fire at some point because you didn't check on a few critical details.

Masonry parged flues are a type of lining used in brick chimneys. A flue lining is a protective layer that lines the inside of a chimney, helping to protect the structure from the corrosive byproducts of combustion, such as creosote and acidic gases. The term "parging" is when you apply a thin layer of mortar or cement to the inside to create a smooth, durable surface. This helps to improve the flow of exhaust gases and prevent the buildup of soot and other combustion byproducts.

They are typically made from clay tile, cast-in-place concrete, or stainless steel, and can be installed in new or existing chimneys. The parging process involves applying a layer of mortar or cement to the interior of the flue lining, smoothing it out, and allowing it to dry. This creates a smooth surface that helps to improve the flow of exhaust gases and prevents the buildup of soot and other combustion byproducts.

Masonry parged flues have several advantages over unlined or poorly lined chimneys. Firstly, they help to prevent the buildup of creosote and other byproducts that can lead to fires. Secondly, they improve the efficiency of heating appliances by improving the flow of exhaust gases, which helps to reduce the amount of heat loss as they escape out of the building.


Flexible Stainless Steel LinersChimney liner

This is a type of flue lining used in chimneys to protect the masonry structure from the corrosive byproducts of burning, such as creosote and acidic gases. They are made from high-grade flexible stainless steel. This means it is easier to install when you need to work in tight spaces and bends.

Flexible stainless steel liners are usually used in existing chimneys that are in need of repair or relining. They can be installed without the need for extensive masonry work, which can be time-consuming and costly. Instead, the liner is simply inserted into the existing chimney and secured in place with a series of clamps and fasteners.

One of the primary advantages here is durability. They are designed to withstand high temperatures and corrosive gases, which can help to extend the lifespan of the chimney and reduce the risk of fires. They are also easy to clean and maintain, which can help to improve the efficiency of heating appliances and reduce the amount of soot and other combustibles that can build up.


A note on installation

Installation should only be carried out by trained professionals, as a bad fitting can lead to serious safety issues such, and at worst, a chimney fire. It is also recommended to have regular chimney inspections and cleaning to ensure that the liner is functioning properly and to prevent any potential chimney fires. Furthermore, flexible stainless steel liners may not be suitable for certain types of appliances or chimneys, so it is important to consult with a professional to determine if this type of liner is appropriate for your specific needs.


Clay, concrete, And Pumice

This is the post-1966 category, mainly...

Clay is a traditional and widely used material for chimney flue liners. It is known for its durability, fire resistance, and ability to withstand high temperatures. Concrete is another popular material, which is typically used for chimney crowns, caps, and other non-flue components. It is strong, long-lasting, and resistant to weathering and corrosion. Pumice is a lightweight volcanic stone that is often used for chimney flue liners due to its insulating properties and excellent resistance to heat and acid.

Each material has its own unique advantages and disadvantages, so it is important to choose the right material for your specific needs. Clay liners are relatively inexpensive and easy to install, but they can crack over time and require regular maintenance to prevent corrosion. Concrete is more durable and requires less maintenance, but it is heavier and can be more challenging to install. Pumice is lightweight and provides excellent insulation, but it can be more expensive than other materials and may require professional installation.

Ultimately, the choice of material for your chimney will depend on various factors such as your budget, the type of fuel you are using, and your specific needs and preferences. Always consult with a specialist who can provide expert advice and help you choose the right material for your construction or repair project. Whatever material you choose, regular maintenance and inspections are essential to ensure the safety and longevity of your chimney.


Prefabricated stainless steel flue systems

Easily assembled and supported, these systems consist of an outer case and inner liner with insulation filling the space in between both materials.
Prefabricated stainless steel flues are typically fitted when a chimney isn’t present.


Twin wall flue

Many new homes are now built without a traditional chimney (this is a trend that has developed since the 1980s). However, if you live in a home without a traditional chimney, you can still have a fireplace - you’ll just need to install a twin-wall flue system. The twin wall flue system is basically one flue inside the other. This gives you enough cooling for the flue to go through a roof, a wall, or a ceiling with safety.


Pre-cast flue

A pre-cast chimney flue is, as you may think, a flue that is built out of a series of concrete blocks and integrated within the walls of your home. You'll normally find pre-cast flues in homes built within the last 20 years. You can spot if a home is using a pre-cast flue by a small ridge vent which is located on the roof line.
So, those are the main types of different flues you’re likely to encounter.


‍What are the different types of chimneys?

Class 1 Chimneys

Most commonly in houses built up until around 1960 -brick-built ( masonry chimneys) and situated either on either an exterior wall on an interior wall. They usually contain multiple flues, too, and can be used with all types of solid fuel fires.


Class 2 Chimneys

These were built from the 1960s onwards. They feature interlocking metal pipes that run through the house and can only be used with specific types of gas fire.‍


A note on factory-built chimneys

Factory-built chimneys, also known as prefabricated or zero-clearance chimneys, are a popular option for homeowners who want to install a chimney quickly and easily. These chimneys are manufactured in a factory and come in a range of sizes and designs to fit different types of heating appliances. They are typically made of stainless steel, galvanized steel, or other lightweight materials and are designed to be installed directly onto the exterior portion of a home or building. Ease of installation is the main factor here.
However, it is important to note that they need to be maintained correctly to ensure their safety and longevity. Improper installation or lack of maintenance can lead to a range of issues such as leaks, corrosion, and damage to the surrounding structure.


More Important Terms: Vents, Connectors & Flues

Chimney terminology can be confusing. Whether you’re doing online research or talking to a professional, you need to "get it" otherwise you're going to run into trouble. Important note: Chimneys technically do vent fuel, but they are not classed as “vents”. So here we go...


Understanding Vents

These take out the flue gasses for appliances that have lower temperatures, for example, gas fireplaces or oil burners. Vents can pass through the house, or there can also be an exterior portion. As long as they are safe from the weather and out of the way of people to the exterior of the house.
Vents need a degree of temperature protection, otherwise, their low-temperature combustion products may be too cool to properly vent. This could cause a dangerous amount of combustible materials to collect in your vent.

You need to expose the vent to the outside so that it can release the byproducts. This is fine as long as the vent is warm enough internally. If the temperature gets a little low, then a fan can be used to help force the smoke up and out.

You don't build your own vents - they are always factory produced and they aren't classed as a chimney, as they can't take the high temperature of something like wood combustion.
However, you can run a vent through a chimney. Just make sure that any other smoke from something like a fireplace is coming up through the appropriate flue.


Did We Miss Anything?

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