​Should I Insulate My Chimney Liner?

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 chimney liner. A basic knowledge of building regulations is vital when installing 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 liners manufactured from high-quality stainless steel that will last many years. A flue liner plays a vital role in efficiently operating 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 temperature difference 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. This creates a good and even constant flow of heat to release back into the room and allows 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, the majority of the time, there may be issues when the surrounding air is cold. This process ultimately causes a reduction in the temperature within the liner, which has the potential to create condensation, thus impacting the efficient release of hot gases into the atmosphere. Allowing the moisture produced by the condensation to flow back down the liner and into your wood-burning stove can cause a multitude of issues and, at best, impact its overall efficiency.

So, in summary, merely insulating your flexible chimney liner 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 on the efficiency of your stove. The so-called "draw" connected with your wood burner is vital to its efficient creation of hot air and in maximising fuel consumption.

When thinking about potential cost savings, there are areas where your stove can be less efficient than it should be, meaning more fuel will be required to maintain a comfortable room temperature. The need for more fuel generates a more significant cost impact, reducing overall cost savings. Modern-day wood-burning stoves are exceptionally well-designed and highly 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 the draw and potentially damage moisture and condensation. Today's modern stoves have an efficiency rating of over 80%, which compares exceptionally well to a traditional coal fire with an average efficiency rating of between 20% and 30%. Even the latest, most inefficient wood-burning stoves will outperform traditional coal fires. A wood-burning stove works best when the appliance operates at or around maximum efficiency.

Do you know what your options are?

No building regulations stipulate that you must insulate a chimney liner when installing it in a chimney stack. The only regulation concerns the gases that must be safely vented from the building. So, by insulating your chimney liner within the chimney cavity, you 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 recommend insulating if your existing chimney is on an outside wall. Also, insulating your chimney liner is a good plan if the chimney stack is large compared to the flue liner diameter or if the chimney stack is particularly tall. 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. This may, over time, cause damage to the flue and the stove as corrosion occurs within the flue liner once condensation is produced.

There are several different methods for insulating your liner. You can cover a flexible liner by blanket-wrapping it with suitable material before inserting it. Or you can pour 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 glass fibre felt, which is long-lasting, non-flammable, strong, and durable. A liner wrap will keep the flue gases hot, improving the draw and reducing the risk of a chimney fire. Installation is simple: sections of liner are wrapped around before being lowered into a chimney or pulled up. Always remember that a chimney must be 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. A register plate must block the chimney from the bottom to use this method. This type of insulation is similar to vermiculite insulation; the granules are poured from the top 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

Accessories: Clay Pipe Adaptors / Sump Adaptor / Sealants / Closure Plates

Suppose your stack is located internally within the building. In that case, 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.

Insulating is a simple procedure; however, it will add costs to your project, so it is a personal choice in most cases.