​Should I Insulate My Chimney Liner?

Here at Nationwide Chimney Components, we like to offer friendly advice on many questions from 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 where the guidelines/regulations are somewhat vague. A common question is whether a flexible flue liner within a chimney stack can be insulating. At NCC, we stock high-quality stainless steel chimney liners that 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 operates under negative pressure created by the temperature difference, ensuring that 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, consistent flow of heat to be released back into the room and allows hot gases to escape through the liner.

Ensuring your flexible chimney flue is insulated offers many benefits for controlling the release of hot gases. In simple terms, while a non-insulated chimney flue may work perfectly well, most of the time, there are issues when the surrounding air is cold. This process ultimately reduces the temperature within the liner, which can lead to condensation, thereby affecting the efficient release of hot gases into the atmosphere. Allowing condensation to flow back down the liner and into your wood-burning stove can cause a multitude of issues and, at best, reduce 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 prevents the formation of unwanted condensation and moisture, which in turn will noticeably impact your stove's efficiency. The so-called "draw" connected to your wood burner is vital for efficient heating and maximising fuel efficiency.

When considering potential cost savings, there are areas where your stove may be less efficient than it should be, requiring more fuel to maintain a comfortable room temperature. The need for more fuel has a greater impact on costs, reducing overall savings. Modern-day wood-burning stoves are exceptionally well-designed and highly efficient; there are still areas where users can help improve performance.

So, to answer the question, the potential for condensation in an uninsulated flexible flue liner will affect the draw and could cause damage due to moisture. Today's modern stoves have an efficiency rating of over 80%, which compares favourably to a traditional coal fire, which has an average efficiency rating of 20% to 30%. Even the latest, most inefficient wood-burning stoves will outperform traditional coal fires. A wood-burning stove works best when it operates at or near 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 idea if the chimney stack is much larger than the flue liner diameter or if the stack is particularly tall. This process will increase the rate at which those gases escape by keeping the flue gases warm, thereby reducing the chance of condensation forming on the liner. As previously discussed, cooling gases can cause condensation to flow down the flexible liner and enter the multi-fuel wood burner. This may, over time, damage the flue and the stove, as corrosion occurs within the flue liner when condensation forms.

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 the flue during or after 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, insulation is not a priority, as the house's warmth will provide insulation for the flue liner and chimney. However, it is still possible to carry out these works to achieve optimal performance of the flue system.

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