What Is a Single Wall Flue Pipe?
A single wall flue pipe consists of one layer of stainless steel, typically 0.4–0.6mm thick. It is the most basic and affordable type of flue pipe and is designed for use inside the room where the stove is installed — never inside walls, ceilings, or unheated spaces.
Advantages:
- Lower purchase price
- Easier to connect directly to the stove
- Widely available in standard diameters
Disadvantages:
- Outer surface becomes very hot — a burn hazard
- Requires a minimum clearance of 200–300mm from combustible materials
- Not suitable for passing through walls, floors, or roof spaces
What Is a Double Wall Flue Pipe?
A double wall flue pipe (also called twin wall or insulated flue pipe) has two layers of stainless steel with a layer of mineral wool insulation in between, typically 25mm, 32mm or 50mm thick. This construction keeps the outer surface cool to the touch and maintains the flue gas temperature, which improves draft and reduces condensation.
Advantages:
- Outer surface stays cool — safe near combustible materials
- Can pass through walls, ceilings, roof spaces and outside the building
- Better draft performance due to maintained flue gas temperature
- Reduced risk of condensation and tar deposits
- Compliant with safety regulations for concealed installations
Disadvantages:
- Higher purchase price than single wall
- Heavier and requires proper bracketing and support
The Simple Rule: Where Is the Pipe?
| Location | Single Wall | Double Wall |
|---|---|---|
| Visible inside the room | ✅ Yes | ✅ Yes |
| Inside a wall or partition | ❌ No | ✅ Yes |
| Through a ceiling or floor | ❌ No | ✅ Yes |
| In an unheated attic or roof space | ❌ No | ✅ Yes |
| Outside the building | ❌ No | ✅ Yes |
| Through an existing masonry chimney | ❌ No | ✅ Yes (liner) |
In practice, most installations use a combination: single wall pipe from the stove to the ceiling or wll, then double wall from the ceiling upward through the roof, or sidewards through the wall.
Does Insulation Thickness Matter?
Yes. Double wall flue pipes come in two common insulation thicknesses:
25mm insulation is suitable for most standard residential installations where the pipe runs through a heated or semi-heated space for a short distance.
50mm insulation is recommended when the pipe runs through a long unheated section (such as a cold attic or outside the building), in colder climates, or when using a pellet stove which produces lower flue gas temperatures. The thicker insulation better maintains draft and prevents condensation.
What About Diameter?
Single wall and double wall pipes are both available in standard diameters: 80mm, 100mm, 125mm, 150mm, 180mm and 200mm. The correct diameter is determined by your stove's flue outlet — never reduce this diameter as it restricts draft. When in doubt, go one size up rather than down.
Standards by Country
Flue pipe regulations differ per country. Always check with your local authority or a certified installer before purchasing.
