Product Description

TWPro 125mm Twin Wall Insulated Flue Pipe 500mm – Matt Black

Model: 37-125-011

Build a safe and durable insulated chimney with the TWPro 125mm Twin Wall Insulated Flue Pipe. This rigid 500mm section provides an effective installed length of approximately 465mm after the push-fit joint overlaps with the next component.

The pipe features a 316L stainless-steel inner casing, high-density mineral wool insulation and a matt-black 304-grade stainless-steel outer casing. Therefore, it combines strong construction with a smart finish for visible internal or external chimney routes.

This component connects to other compatible 125mm TWPro chimney parts through the FitSystem push-fit joint. In addition, the supplied locking band helps secure the connection.

Product at a Glance

• 125mm nominal internal flue diameter
• 500mm overall pipe length
• Approximately 465mm effective installed length
• Rigid insulated twin-wall construction
• Suitable for internal and external chimney routes
• 316L stainless-steel inner casing
• 304-grade stainless-steel outer casing
• High-temperature matt-black external coating
• 25mm high-density mineral wool insulation
• Push-fit FitSystem connection
• Supplied with a locking band
• Suitable for compatible solid-fuel, gas and oil appliances
• HETAS approved and CE marked
• T600 temperature classification
• G50 soot-fire resistance classification
• 50mm declared distance to combustible materials
• Product model: 37-125-011

500mm Overall Length and 465mm Installed Length

This pipe measures 500mm from end to end before installation. However, part of the pipe enters the socket of the next TWPro component during assembly.

As a result, each 500mm section adds approximately 465mm to the completed chimney route. Therefore, use the effective installed length rather than the overall product length when calculating the number of pipe sections required.

For example, two 500mm sections do not add a full 1000mm to the chimney. Together, they add approximately 930mm after both joints overlap.

Always allow for adaptors, bends, tees, supports and terminal components when calculating the complete chimney height.

Why Choose a 500mm TWPro Pipe?

A 500mm section provides a practical balance between coverage and flexibility. It covers more distance than a short pipe while remaining easier to position than a full 1000mm length.

Therefore, installers often use a 500mm section to complete the chimney height, adjust the location of a bend or reach the correct terminal position. It can also help when restricted access makes a longer pipe difficult to handle.

However, this product has a fixed length. It does not provide adjustment. If the installation needs a precise final measurement, choose a compatible TWPro adjustable pipe where appropriate.

Key Features

• Rigid 500mm insulated chimney section
• Adds approximately 465mm to the installed flue route
• Suitable for vertical and approved angled chimney sections
• Maintains a continuous 125mm internal flue diameter
• High-grade stainless-steel inner and outer casings
• Insulation helps maintain flue-gas temperature
• Fully welded construction provides strength and durability
• Matt-black finish suits both modern and traditional properties
• Push-fit joint supports quick and straightforward assembly
• Locking band secures the connection
• Compatible with matching TWPro pipes, bends, tees and terminals

TWPro 125mm 500mm Pipe Specification

• Download the TWPro Matt Black information sheet
• View the TWPro installation diagram
• Read why we recommend TWPro twin-wall flue
• Product type: rigid insulated twin-wall flue pipe
• Nominal internal diameter: 125mm
• Overall length: 500mm
• Effective installed length: approximately 465mm
• Inner casing: 0.4mm 316L-grade stainless steel
• Outer casing: 0.4mm 304-grade stainless steel
• Outer finish: high-temperature matt-black coating
• Insulation: 25mm high-density mineral wool
• Construction: fully welded
• Joint method: push fit with locking band
• Locking band: included
• Temperature classification: T600
• Declared distance to combustible materials: 50mm
• System warranty: 25 years, subject to terms and conditions
• Paint-finish warranty: 2 years, subject to terms and conditions
• Product code: 37-125-011

Approvals and Classifications

• HETAS approved
• CE marked
• EN 1856-1 T600 N1 W V2 L50040 G50
• EN 1856-1 T200 P1 W V2 L50040 O20

The T600 designation classifies the relevant chimney arrangement for flue-gas temperatures up to 600°C. In addition, the G50 designation identifies a soot-fire-resistant arrangement with a declared distance of 50mm from combustible materials.

However, the correct classification depends on the appliance, fuel and complete chimney design. Therefore, always follow the appliance instructions and the TWPro installation guide.

Suitable Applications

This 125mm TWPro insulated flue pipe may suit correctly specified heating appliances such as:

• Wood-burning stoves
• Multifuel stoves
• Compatible solid-fuel appliances
• Gas coal-effect fires
• Gas boilers
• Oil-fired boilers
• Other compatible gas and oil appliances

However, the appliance outlet size alone does not confirm the correct chimney diameter. First, check the appliance manufacturer’s instructions. Next, confirm the required chimney classification. Finally, make sure the complete route complies with Building Regulations and the TWPro installation guide.

Suitable for Internal and External Chimney Routes

You can use this insulated section as part of a correctly designed internal or external TWPro chimney.

For an internal route, the chimney may rise above the appliance and continue through upper floors and the roof. However, installers must use the correct ceiling supports, fire stops, enclosure details and roof flashing components.

Alternatively, an external route may pass through a wall before rising up the outside of the building. In this case, use the correct wall sleeve, tee, supports, wall bands and terminal.

The chimney route, height and support arrangement must suit the property and appliance. Therefore, ask a competent installer to design the complete system rather than selecting individual components in isolation.

How Twin-Wall Insulation Helps

The mineral wool layer sits between the inner flue and outer casing. This insulation helps retain heat within the chimney as combustion gases travel upwards.

Warmer flue gases can support chimney draught and help reduce condensation. In addition, the insulation lowers heat transfer to the outer wall when compared with single-wall stove pipe.

However, insulated construction does not make the outside of the chimney safe to touch. The pipe can still become hot during use. Therefore, maintain the required clearances and prevent accidental contact where necessary.

Strong Stainless-Steel Construction

The inner casing uses corrosion-resistant 316L-grade stainless steel. This inner surface carries the combustion gases through the chimney.

Meanwhile, the outer casing uses 304-grade stainless steel with a high-temperature matt-black coating. As a result, the pipe provides weather resistance and a smart appearance for visible chimney installations.

The fully welded construction also provides strength and durability. Consequently, the section can form part of a long-lasting chimney when installers fit, support and maintain it correctly.

Matt-Black Finish

The smooth matt-black outer surface complements black stoves, vitreous enamel connecting pipes and other TWPro matt-black components.

Therefore, the pipe works well in rooms where part of the insulated chimney remains visible. It can also create a less reflective appearance on an external chimney route.

However, installation tools and rough handling can damage the coating. Handle the pipe carefully and follow the manufacturer’s guidance for touching up minor marks with a compatible high-temperature finish.

Installation Guidance

Before installation, check the pipe for transport damage, dents or coating defects. Also, confirm that both joint ends remain clean and correctly formed.

Push the pipe fully into the next compatible TWPro component. Then fit and secure the supplied locking band around the joint. Finally, check that the pipe remains straight and that the joint has fully engaged.

Install the sections in the direction shown in the TWPro instructions. Correct joint orientation helps keep condensate and combustion deposits inside the flue.

Do not cut this fixed pipe to alter its length unless the manufacturer specifically permits the modification. Instead, use a suitable standard or adjustable TWPro section to achieve the required chimney height.

Locking Band and FitSystem Joint

The TWPro FitSystem uses a push-fit connection between matching components. Once the two sections engage, the locking band secures the joint.

This design makes assembly straightforward. However, the locking band must sit in the correct position and close fully.

A locking band connects the components but does not provide structural chimney support. Therefore, use the correct wall bands, roof supports and other support components throughout the chimney route.

Distance to Combustible Materials

Maintain at least 50mm between the TWPro insulated chimney and combustible materials for the relevant T600 G50 system arrangement.

Combustible materials can include timber, roof structures, insulation, furniture and other heat-sensitive products. Furthermore, plasterboard may form part of a timber structure and should not automatically count as non-combustible.

Keep the required air gap clear. Do not fill it with insulation or building materials unless the manufacturer provides a tested component for that exact purpose.

The appliance or another part of the installation may require a greater clearance. Therefore, always follow the largest distance stated in the appliance instructions, chimney instructions or relevant regulations.

Single Wall and Twin Wall Explained

Single-wall stove pipe has one steel wall and no insulation. Installers normally use it as a visible connecting pipe between the appliance and chimney.

In contrast, TWPro uses an inner flue, mineral wool insulation and a stainless-steel outer casing. Therefore, it can form a chimney route through a building or externally when installers use the correct components and clearances.

Single-wall stove pipe must not pass through walls, ceilings, floors, roofs or concealed spaces. Use a suitable adaptor to change to TWPro twin wall before any building penetration.

Supporting the Chimney

Do not expect the appliance, adaptor or lower pipe section to carry the weight of the complete chimney. Instead, use the correct TWPro supports throughout the route.

External systems normally need wall bands at the intervals stated by the manufacturer. In addition, tees and long vertical sections may require load-bearing supports.

Internal routes may require ceiling or roof supports. The installer must also consider lateral movement, wind loading and the permitted unsupported height above the final support.

Can the Pipe Run Horizontally?

Twin-wall chimney systems should rise as directly as possible. Horizontal or near-horizontal runs can reduce draught and collect combustion deposits.

Therefore, only use offsets and non-vertical sections where the appliance instructions, chimney design and Building Regulations permit them. Maintain the required upward rise towards the terminal.

Ask a competent installer to confirm the route before ordering the pipe sections and bends.

Can I Mix TWPro with Another Chimney Brand?

Do not connect this pipe to another manufacturer’s twin-wall system unless both manufacturers provide written approval.

Different systems can use different outer diameters, joint depths, insulation specifications and locking methods. Therefore, two products with a stated 125mm internal diameter may not connect safely.

Using matching TWPro components helps preserve the tested system classification and creates a secure, consistent chimney installation.

Maintenance and Chimney Sweeping

Inspect the pipe, joints, supports and locking bands during routine chimney maintenance. Look for movement, corrosion, soot staining or damage to the matt-black finish.

Arrange chimney sweeping at intervals that suit the appliance, fuel and frequency of use. In addition, make sure the complete chimney provides suitable access for inspection and cleaning.

Replace any component that becomes badly corroded, distorted, damaged or insecure. Furthermore, arrange a professional inspection if you notice smoke leakage, poor draught or a change in appliance performance.

Why Choose TWPro?

TWPro combines a durable 316L stainless-steel inner casing with a strong 304-grade stainless-steel outer casing. In addition, the mineral wool insulation helps retain heat and supports a stable flue temperature.

The FitSystem push-fit joint makes assembly straightforward, while the locking band secures each connection. Furthermore, the wide range of matching pipes, bends, tees, supports, flashings and terminals allows installers to create a complete chimney from compatible parts.

Finally, the smooth matt-black finish creates a professional appearance for modern and traditional properties.

Why Buy from SNH Tradecentre?

• Specialist stove, chimney and flue-system supplier
• Extensive range of matching 125mm TWPro components
• Practical product advice from an experienced team
• Nationwide UK delivery options
• Secure online ordering
• Trade counter in Birchington, Kent
• Support before and after your purchase

Need help calculating the pipe lengths or choosing the correct support components? Call SNH Tradecentre on 01843 842727 before ordering.

Frequently Asked Questions

What is the overall length of this pipe?

The pipe has an overall length of 500mm before installation.

What is the effective installed length?

The section adds approximately 465mm to the completed chimney because part of the pipe enters the adjoining component.

What diameter is the pipe?

It has a nominal internal flue diameter of 125mm, which is approximately 5 inches.

Is 125mm the outside diameter?

No. The 125mm measurement refers to the internal flue diameter. The insulation and outer casing make the overall external diameter larger.

Does the pipe include a locking band?

Yes. The supplied locking band secures the push-fit connection to the next compatible TWPro component.

Can I use it with a wood-burning stove?

Yes, it may suit compatible wood-burning and multifuel stoves. However, check the required flue diameter and chimney specification in the appliance instructions.

Can this pipe pass through a wall or ceiling?

Twin-wall insulated chimney can pass through building structures when installers use the correct fire stops, support components, sleeves, flashings and clearances.

How far must it remain from combustible materials?

The relevant T600 G50 system has a declared distance of 50mm from combustible materials. However, another part of the installation may require a greater clearance.

Can I cut the pipe to make it shorter?

Avoid cutting a fixed TWPro pipe. Instead, use a compatible adjustable section or a different standard length to achieve the required measurement.

Can I connect it to another twin-wall chimney brand?

Do not mix chimney brands unless both manufacturers provide written approval. Similar-looking components may use incompatible joint systems.

What is the product model?

The product model is 37-125-011.