Whats in a Twin Wall flue System?

Where a brick built chimney is not possible to be installed, then an easy option is to have a twin wall metal flue. These needs to terminate as a brick built chimney would, but take up less space and could be installed in as little as a day.

The other advantages a twin wall flue can bring is that it is insulated, this means that the flue gasses can retain much of the energy needed to allow the flue gases to escape to the atmosphere as quickly as possible, in turn meaning these gases have less time to condensate, thus meaning the draft within the flue way can be stronger to help make the fire at the base of the flue system work to its best potential. This insulation also allows the flue system to be placed closer to combustibles (Typically 50mm) like roof joist, plaster board and other possible combustibles that you may find along its route.

Most twin wall flue systems are tested to withstand temperatures of 600 degrees Celsius, for no more than 30 minutes at a time. This is a standard test that all Class I flues must pass due to chimney fires.

The standard twin wall flue system is two steel pipes, an inner and outer. These are secured together so they are rigid to each other. The insulation between these two pipes is Rockwool insulation. This material gives reasonable values however. This will start to break down at around 450 degrees Celsius. These two factors are why most twin wall flues have a 10 year warranty.

Most twin wall flues are put to work with an appliance of some description, that through normal operation (Door closed) the flue gas temperature is between 195-350 degrees Celsius. However when the glass/door is opened then you get a rush of air coming into the flue, taking the heat that the appliance has in its fire area up the flue, the flue gas temperature can jump to around 600 degrees Plus. This is where damage can occur. The inner flue pipe wants to expand, yet the outer (Cooler) pipe does not. And so the metal can slowly become weaker over a period of time. Secondly the insulation will start to break down and compact in the flue; this means you end up with points in the flue system that no longer has a good insulation value.

If you are unlucky enough to have a chimney fire, then these weak points become dangerous. And if one of these weak points is near a combustible, then it could be possible to cause a fire by transference of heat. More likely, these cold spots are where condensates will gather and the effectiveness of the flue system will be greatly reduced.

The Metaloterm EOntop AT system is different in two key ways. And this is why it has been given a 30 year guarantee, even if you have repeated chimney fires.

Firstly, the construction. The two pipes are wired together, allowing the inner to move independently to the external pipe. This does not put stress on to the metals when it heats and cools at a different rate. So you will not get metal fractures in the flue.

Secondly, the insulation is made from Carbide Silica. This natural material has great insulation property’s, it also has a melting point of 1700 Degrees Celsius. This means that the temperatures achieved with a wood burning appliance or a chimney fire will not break down the thermal properties of this insulation. Even with repeated chimney fires gaining temperatures of 650 degrees Celsius +. Let alone the normal operation of a wood burning appliance of opening the glass door to refuel the appliance.

In summary

If you have a flue system of any description you should always burn the correct fuel and limit slumbering of the fire to the absolute minimum. You should never burn wet or unseasoned wood, and you should always have your flue swept by a qualified sweep each year regardless of how many fires you have or have not had, to maintain the flue route is clean.

If however you are unlucky enough to have a chimney fire, will your flue system be safe while the chimney fire is happening? If you do not have a Metaloterm EOntop AT system then you should think about having it changed for a new system.

So when you are spending a lot of money on a wood stove and flue system, would you rather a flue system with a 10 year warranty or a flue system with a 30 year guarantee that has factual arguments to give it this long life. We at Anglia Fireplaces only sell Metaloterm EOntop AT for any customer wanting a twin wall metal flue system.

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