Here at Nationwide Chimney Components, we like to give friendly advice on many questions posed by both public and trade customers. This post looks into whether you should insulate your flexible flue liner. Having a basic knowledge of building regulations is vital when looking to install a wood-burning or solid fuel stove. There are several areas in which the guidelines/regulations are a little vague. A common question that often needs answering is the potential insulating of a flexible flue liner within a chimney stack. At NCC, we stock stainless steel chimney liner that is manufactured from high-quality stainless steel and will last for many years. A flue liner plays a vital role in the efficient operation of any wood burning or solid fuel stove, so do you need to insulate the liner?
The primary purpose of a liner is to funnel hot gases out of your stove into the atmosphere, via a masonry chimney stack. The liner works under negative pressure created between the difference in temperature to ensure that the harmful gases are drawn vertically up the flue system into the atmosphere. A stainless steel chimney liner is a pivotal part of the fuel-burning process. Creating not only a good and even constant flow of heat to release back into the room but also allowing hot gases to escape out via the liner.
Ensuring your flexible chimney flue is insulated provides many benefits when it comes to controlling the release of hot gases. In simple terms, while a non-insulated chimney flue may work perfectly well, for the majority of the time, there may be resulting issues when the surrounding air is cold. This process ultimately causes a reduction in the temperature within the liner with the potential to create condensation and thus impacting the efficient release of the hot gases into the atmosphere. Allowing the moisture created by the condensation to flow back down the liner and into your wood-burning stove can cause a multitude of issues and at best impacting its overall efficiency.
So in summary, merely by insulating your flexible chimney liner it will ensure that the hot gases remain hot and are safely released into the atmosphere as quickly as possible. It also negates the potential creation of unwanted condensation and moisture, which in turn will have a noticeable impact upon the efficiency of your stove. The so-called "draw" connected with your wood burner is vital to not only its efficient creation of hot air but also in maximising fuel consumption.
When thinking about potential cost savings, there are areas where your stove can be less efficient than it should, meaning more fuel will be required to maintain comfortable room temperature. The need for more fuel generates a more significant cost impact, which then leads to a reduction in overall cost savings. Modern-day wood-burning stoves are exceptionally well designed and extremely efficient; there are still areas where the user can assist and increase performance.
So to answer the question, the potential creation of condensation in an uninsulated flexible flue liner will impact on the draw as well as cause potentially damaging moisture and condensation. Today's modern stoves will have efficiency ratings over 80%, which compares exceptionally well in comparison to a traditional coal fire which has an average efficiency rating of between 20% and 30%. Even the latest most inefficient of wood-burning stoves will still outperform a traditional coal fire. A wood-burning stove works best when the appliance is operating at or around maximum efficiency.
So What Are Your Chimney Liner Options?
There are no building regulations that stipulates you must insulate a chimney liner when installing in a chimney stack. The only regulation is concerning the gases that must be safely taken vented from the building. So by insulating your chimney liner, within the chimney cavity, this will ensure that the gases are safely vented and will travel directly up from the multi-fuel stove and out through the chimney top.
We would advise insulating if your existing chimney is located on an outside wall. Also if the chimney stack is large in comparison to the flue liner diameter or if the chimney stack is particularly tall, then insulating your chimney liner is a good plan to implement. This process will increase the speed of those gases escaping by keeping the flue gases warm and subsequently reduce the chance of condensation forming on the liner. As previously discussed, cooling gases can result in condensation flowing down the flexible liner and entering the multi-fuel wood burner itself. This may, over time, cause damage to the flue and the stove as corrosion takes place within the flue liner once condensation is produced.
There are several different methods for insulating your liner. You can cover a flexible liner before inserting it by blanket-wrapping it with suitable material. Or by pouring Vermiculite, Perlite or Leca granules into the air gap between the liner and flue after/during installation.
Lightweight flue liner insulation is usually made from a glass fibre felt material which is long-lasting non-flammable, strong and durable. A liner wrap will keep the flue gases hot, which will improve the draw and reduce the risk of a chimney fire. Installation is simple with sections of liner wrapped around before lowering the liner into a chimney or pulling up. Always remember that a chimney must be first swept before installing a flue liner, never attempt to fit a liner without first sweeping the chimney.
An alternative option is to use backfill insulation for chimney flue liners. This is used to insulate around a chimney liner where there is not enough room to fit Rockwool insulation and where you do not want to use Chimwrap type products. To be able to use this method, a register plate must be used to block the chimney from the bottom. This type of insulation is similar to vermiculite insulation and the granules are poured from the top of the chimney around the chimney flue liner. Unlike vermiculite, it will not compress if it gets damp/wet.
Some products worth considering are.
Insulation: Micafil Chimney Insulation
Liner: Flex Liner
If your stack is located internally within the building, then insulating is not a priority as the warmth of the house will offer insulation for the flue liner and the chimney. However, it is still possible to carry out these works to give the best performance of the flue system.
The process of insulating is a simple procedure; however, it will add costs to your project, so it is a personal choice in most cases.