DUPLICATE – Flexible flue liner installations

Stainless steel flexible flue liners are cylindrical in shape and are manufactured compressing two layers of steel together. The grade of the steel used is either 316L or 904L.

How the layers are brought together, and which steel is used varies between manufacturers.

The liners span the full length of the chimney in one continuous piece. They attach to the cowl at the top, and an adapter at the bottom.

They are designed to be relatively smooth on the inside. This makes it difficult for the waste products of a fire to stick to them and even so, the brushes used when sweeping a flue each year can easily remove the ash and soot.

Therefore, a flexible flue liner flue system is professionally recognised, and is considered a safe and cost-effective way of using an existing chimney.

The flexi liners are relatively flexible – they can be bent. Bending a liner is important and often required as existing chimneys are not always straight. In fact, most pre-existing chimneys have at least one bend throughout the run from chimney pot to fireplace. Thus, being able to bend the liner is essential.

However, the amount of bending of a liner is restricted as at some point, if it is bent too much, it will likely tear. We’ve found that poor quality and cheap liners tear easily. In other words, they are best avoided.

The liners are continuous, cylindrical, and relatively smooth. Almost identical to the twin wall flue systems that we use (when you don’t have an existing chimney!).

The flues will also closely match the outlet of your stove - the area where the waste leaves your stove.

The result means that the flue is designed to be as safe and efficient as possible.

There are many reasons for this. In short:

• Waste products find it hard to stick to the inner lining.
• The smaller diameter flues mean there’s less volume to heat so the heat can easily rise and take the waste products along with it.
• They are easy to clean.
• They increase the efficiency of the stove by allowing it to perform without being clogged by the waste products.

The long answer is available by following this link and is for the geeks amongst us!

It explains about how stoves are more effective and efficient compared to open fires, why using the right techniques is so important in producing less harmful waste products and more heat, and why the construction of old flues and old sweeping techniques damaged old flue systems. Thus, why relining existing flues is important to improve safety and efficiency.

(ADMIN: LINK TO: Reasons for a new flue).

If we cannot clearly see the whole length of the existing flue, it is very likely that we will recommend and direct you to choose a system that can operate with a 5” diameter flue system. The stove you have plays a significant factor in this.

Most manufacturers will recommend that the flue should be a maximum 6” in diameter, which will either match or closely resemble the stove’s outlet that in turn improves the stoves performance.

Before the liner is installed the flue is swept.

Due to the construction of some chimneys, the flexi liners don’t always fit; sometimes the flue is blocked from damaged chimneys (ADMIN: LINK TO DAMAGED CHIMNEYS), or from birds nesting (ADMIN: LINK TO BIRDS NEST). If you don’t have the correct cowl to prevent birds nesting, they will return year after year and add to the nest. We’ve seen nests that have filled the entire chimney/flue!

Sometimes the flue is too narrow or has pre-existing sharp bends.

Therefore, if we can’t see all the way up the flue (such as a large, exposed inglenook fireplace), we will advise the smallest diameter flue liner is chosen, which is typically 5” or 125mm in diameter. This provides the best chance of a successful installation at the least cost. If flues need unblocking, installation companies will have clauses that cover the issues involved with this.

Typically, extra labour and materials are used to free the liner and then make good afterwards. If the blockage is a bend within the flue that is too tight to allow the passage of the liner, located behind a wall in a bedroom, then if the installation needs to go ahead, the wall will be opened, the bend removed (literally removing masonry) and the area patched up and made good by blocking up the hole we’ve created and plastering over it.

This can be messy and loud work often at an uncomfortable height and it may take anything from 2 hours to another full day.

If you have a chimney that stops in the loft, we will use a flexible flue liner combined with a twin wall flue to install your stove. For more information click here.

Blazing Burners disagrees with the use of smokeless fuel. Over the course of each year, we receive calls to attend a property that has a damaged flue liner -often noticed when the chimney sweep has either got their rods stuck or more likely part of the liner has come down into the stove. We’ve had to replace only one of our own flue liners over the 10 years we’ve been installing. The common factor with all these issues is smokeless fuel.

Smokeless fuel is a type of fossil fuel that is like coal. Coal (bituminous) is outlawed for use on stoves, mostly because it burns too hot. Whereas smokeless fuel is accepted as a safe fuel to use. It is called smokeless fuel because it has no volatile matter and volatile matter produces smoke.

We personally think that it still smokes, but maybe smokes less than coal.

User error is rife with smokeless fuel. And this tends to produce smoke. In our opinion user error also leads to it damaging liners and stoves – often irreparably. Consumers often overload the fuel which means it burns too hot for the system to cope with, which produces a lot of ash. Mix it with water (logs and/or rain) and creosote is easily formed.

Creosote is a tar like substance that easily damages flues, and is a significant factor involved with chimney fires as although it clogs up flues, it is still highly flammable.

Simply put, if you use smokeless fuel, there’s too much chance for it to go wrong.

It may be the cheaper fuel but upgrading the liner and the gamble of having to replace everything in as little as 3 years just isn’t worth it in our opinion.

Wood, on the other hand, is a much more user and planet friendly fuel; it’s not a fossil fuel and is also considered carbon neutral as it releases the same amount of carbon if it was burned or left to rot in the ground. Just make sure your wood is dry (properly seasoned or kiln-dried) and ideally sourced locally from well-managed local woodlands and you’re not going to go far wrong. Combine it with Eco-logs or even switch to these wood briquettes and you’ll be doing the planet an even bigger favour!

So, although the solid fuel industry recommends the use of smokeless fuel, combined with a more expensive 904L graded liner (for existing chimneys), we at Blazing Burners strongly recommend that you steer clear of it.

For more advice on fuel and how to use your stove correctly, click here.

We think that the actual quality of the flexible flue liners varies significantly. There are many brands available. They can be manufactured in different ways, and some are more durable than others. We consider some of these to be cheap and poorly constructed, whereas others are significantly more robust.

The cheap ones can tear or dent and unravel easily. We have literally seen brand new liners unravel. We have also removed many poor-quality liners that have been damaged from poor use and even from being swept.

The liners are manufactured using two layers of stainless steel. A lesser grade one and an upper graded steel – 316L and 904L. The difference is mostly on how the steel responds to heat.

Typically, wood burns at a lower temperature to smokeless fuel and as the 904L is designed to withstand higher temperatures, 316L is designed and recommended to use with wood, whereas 904L is used for smokeless fuel use.

Coal is not permitted on stoves; it burns hotter than smokeless fuel and can therefore damage or destroy stoves and flues quite easily.

We’ve found that the incorrect use of smokeless fuel can also cause significant and irreparable damage to a system. Therefore, we only recommend the use of recognised wood products as the fuel for stoves. See above (Wood vs smokeless fuel) for more information on why we disagree with using smokeless fuel.

316L – for use with wood burning

For the 316L grade liners, manufacturers will either choose two layers of 316L or they may choose a layer of 316L and a layer of 904L. The latter being more superior and accommodating occasional overuse. You’ll find this combination (316/904) in the more expensive liners.

904L – smokeless fuel use

904L liners should be made using a 904L/904L combination.

All the liners are tested and given a product designation number. They are tested against many conditions to demonstrate how they perform.

Important tests for a liner are how they resist condensate, corrosion, and temperature including soot fire resistance.

W3G

One manufacturer has engineered a completely new liner that is able to withstand extreme conditions and they offer a lifetime warranty with it.

They called it W3G which is direct reference to its remarkable product designation number. Essentially it works incredibly well with the new eco design stoves.

Although the new classification and approval of Eco-stoves means that you are getting an incredibly efficient stove, it comes with a problem that is being addressed with the W3G liner.

The problem with this because the eco stoves are so efficient, there is less heat being discharged up the flue when compared to the less efficient standard stoves. Essentially this means that the flue has a chance to cool down and in doing so, any moisture that would normally be formed when the waste products meet the air, is now being formed within the flue. The moisture is being known to corrode flexible flue liners. The W3G liners have been engineered and designed to withstand this issue and are becoming increasingly popular. However, they come with an added expense as lining a standard two-storey chimney will add an extra £350 to your bill. Is it worth it? We think so.

And guess who manufacturers the liner…yep, Dura Flue. The same company where we buy all our flex and twin wall flues from.

Click on the links for more information on these flue systems.

W3G

316L & 904L

Twin wall 5” and 6” (DTW) – Chrome or Black

In some instances, the flue may need insulating. This is recommended when the flue liner has lots of space around it. Insulating the flue will maintain the heat within the flue and thus will aid all by-products and composites of combustion to be expelled from your flue. The hot air will remain mostly hot throughout the flue, and because hot air rises, it will carry all these harmful products until they are expelled from the terminal. Otherwise, the flue may get too cold, and these harmful and tarring products may congregate within the flue, which in turn could lead to problems and dangers such as blockages, chimney fires, or condensation forming which may also damage the flue liner. A W3G (ADMIN – LINK TO W3G) flexi liner may help counteract this problem, but it is not designed to completely prevent issues related to heat dissipating within the flue – since this may lead to smoke spillage. (ADMIN; SMOKE SPILLAGE LINK)

There are two methods that we will use to insulate a flexible flue liner.

The first approach involves wrapping the flue in a fireproof blanket. There are many names for this such as “Thermaflue” and “Chimwrap”. This technique is great when you have a large void such as an inglenook fireplace.

The second approach uses a loose backfill incorporating either Leca or Vermiculite. Both of which are excellent natural insulators originating from either clay or rock respectively.

We will be able to advise you if your flue will need insulating and provide an estimate based on what type and how much insulation is required.

Access to the pot is an important factor as performing this work from ladders is gruelling - and almost impossible in high winds and torrential rain.

A labour charge will be applied as each process will add to the time involved and the materials will be extra too.

Two-storey houses will cost from £650 upwards depending on access and the type of insulation required.

If you are interested or want to know if your flue would benefit from insulation and what the cost would be, please check out what we would require by following this link.

All manufacturers will provide warranties on their flue products.

The warranties are conditional. They come with conditions. Typically, the conditions are as follow:

• The flue is installed by a company/installer registered as competent installer. Blazing Burners is HETAS registered (company reg no. 4484, installer reg no: 17124)
• The installation must comply with building regulations
• The stove must be serviced annually
• The flue must be swept annually
• The correct fuel must be used

Warranties vary from between 10 years to a lifetime depending on the manufacturer.

The flue we use is manufactured from Flue and Ducting Ltd and are known as Dura Flue for the flexible flue liners and Dura Twin Wall (DTW) for the twin wall flue systems.

They have set up a “no quibble warranty”. It’s a very honest way of stating that if you can reasonably state why there is an issue, they’ll sort it out.

We’ve never had to fall back on their warranties as their products are brilliant.

But if we needed to, we’re confident that we’ll be supported – meaning you’ll be supported too.

The same ideology behind this warranty applies with what you get from Blazing Burners.

We always aim to help our existing customers as much as possible. If we discover that the problem has come from incorrect use or user error, we’ll do our best to help and we’ll significantly reduce our labour costs, but we must break even.

We’ve only had to rely on this once and it was because of an inferior flue that was used in conjunction with user error with smokeless fuel. We fitted a brand new 316L liner and advised our customer to solely use wood products. The whole installation was performed for less than £400.

We’d like to think that is fair practice.

Our techniques are tried and tested over many years of being established as a successful HETAS registered installation company.

We’ve performed close to a thousand installations since we started over 10 years ago.

Approximately 1/3 of these installations have involved some type of remedial work to a fireplace or chimney.

Over half were performed using a flexible flue liner system.

We only use the best materials available to us.

We offer an extensive after care service that includes a discounted annual service package – taking care of both your flue and stove.

We have extensive public liability insurance (and are happy to say that we’ve never had to use it!).

We are friendly, efficient, professional and pay a lot of attention to detail.

For more information on how we perform, what we do and what we need to get your installation underway, just follow the highlighted links!

Flexi liners are manufactured by compressing two layers of steel together through a machine that forms the cylindrical shape.

The actual method of construction changes from manufacturer to manufacturer and the difference in quality is very real. We have used a wide range of different liners from many manufacturers, and for the past 7 years we have settled with the same one which we still think is the best available liner in the industry.

It’s called Dura Flue and it is a product of German engineering, although they are manufactured by Flue and Ducting Ltd which started out as a small Manchester based company and now has 4 depots in the UK.

Dura Flue has a reputation of being a tough and solid liner and notoriously it is not as bendy as the other liners. Therefore, some installers choose the bendier liners.

However, we have previously noted that the bendier liners are more fragile and are more exposed to being torn and dinged during the often-vigorous method involved with installing a flexi liner. Therefore, we have found that there is a fine balance of being too flexible and fragile compared to being able to withstand several bends within an existing chimney.

There are several methods and techniques involved with installing liners around bends, and we have yet to fail in getting a 5” dura flue liner down a chimney that is larger than a 5" diameter.

In comparison, we have had to walk away from jobs years ago when we chose inferior liners that tore during installation.

The conditional warranty that comes with Dura Flue liners is a testament to their quality as they match the longest available in the industry. Click here for a YouTube video on just how tough these liners are!

Dura Flue 316L is our standard go to liner. Upgrading to a W3G liner is a great option we would recommend if you can afford the extra cost – typically £350 for a 2-storey house.