Product Description

TWPro 100mm Single Wall to 125mm Twin Wall Increaser – Matt Black

Model: 37-100-002

Connect a 100mm appliance outlet or single-wall stove pipe to a 125mm TWPro insulated chimney with this TWPro Single Wall to Twin Wall Increaser. The tapered component increases the internal flue diameter from 100mm to 125mm while creating a neat transition into the twin-wall system.

You can fit the lower end to a compatible 100mm appliance outlet, vitreous enamel stove pipe or another approved single-wall connecting pipe. Meanwhile, the upper end connects to a 125mm internal-diameter TWPro insulated chimney section.

Always confirm that increasing from 100mm to 125mm complies with the appliance manufacturer’s instructions. The outlet size alone does not confirm that the appliance or installation can use this adaptor.

Product at a Glance

• Connects 100mm single-wall pipe to 125mm twin-wall chimney
• May also connect a compatible appliance outlet directly to TWPro
• Increases the internal flue diameter by 25mm
• Tapered shape creates a smooth transition
• Compatible with the TWPro matt-black chimney system
• 316L stainless-steel inner casing
• 304-grade stainless-steel outer casing
• High-temperature matt-black external coating
• High-density mineral wool insulation
• Push-fit connection with supplied 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: 37-100-002

What Does This Increaser Connect?

This component creates a transition between two different types and sizes of flue:

• Lower connection: 100mm single-wall stove pipe or compatible appliance outlet
• Upper connection: 125mm internal-diameter TWPro twin-wall insulated chimney

The stated 125mm measurement refers to the internal flue diameter. Because the twin-wall section also contains insulation and an outer casing, its overall outside diameter will be larger.

Therefore, check both connection sizes and the complete product dimensions before ordering. A component described as 125mm twin wall will not have a 125mm external diameter.

Why Use a Single Wall to Twin Wall Increaser?

Single-wall stove pipe normally forms the visible connecting section close to the appliance. However, an insulated twin-wall chimney becomes necessary when the flue route passes through or close to parts of the building structure.

This increaser joins the two systems while also changing the internal diameter from 100mm to 125mm. As a result, it can remove the need for separate adaptor and increasing components where the chimney design calls for this exact transition.

The tapered shape also creates a smoother and neater change than using several separate fittings. Therefore, the completed installation can look less cluttered above the appliance.

Key Features

• Combines a system adaptor and diameter increase in one component
• Connects compatible single-wall pipe to insulated TWPro chimney
• Supports a direct connection from some appliance outlets
• Creates a gradual 100mm to 125mm transition
• Reduces the number of separate joints required
• Strong stainless-steel inner and outer casings
• Insulated upper section helps retain the flue temperature
• Fully welded construction provides strength and durability
• Matt-black finish complements most black stoves and stove pipes
• Supplied locking band secures the TWPro connection

TWPro 100mm to 125mm Increaser Specification

• Download the TWPro Matt Black information sheet
• View the TWPro installation diagram
• Read why we recommend TWPro twin-wall flue
• Product type: single-wall to twin-wall increasing adaptor
• Lower connection: 100mm single wall or compatible appliance outlet
• Upper connection: 125mm internal-diameter TWPro twin wall
• Diameter increase: 25mm
• Inner casing: 0.4mm 316L-grade stainless steel
• Outer casing: 0.4mm 304-grade stainless steel
• Outer finish: high-temperature matt-black coating
• Insulation: high-density compressed 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: 37-100-002

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 system 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

The TWPro 100mm to 125mm increaser may suit correctly specified heating appliances such as:

• Wood-burning stoves
• Multifuel stoves
• Other compatible solid-fuel appliances
• Gas coal-effect fires
• Gas appliances
• Oil-fired appliances

However, this list does not confirm suitability for every appliance. First, check the required flue diameter in the appliance manual. Next, confirm that the manufacturer allows the increase from 100mm to 125mm. Finally, make sure the complete TWPro chimney carries the correct classification for the fuel and appliance.

Can It Connect Directly to the Appliance?

Yes, this increaser can connect some compatible 100mm appliance outlets directly to a 125mm TWPro chimney. However, the connection depends on the appliance spigot dimensions, joint type and installation instructions.

Alternatively, the lower end can connect to compatible 100mm single-wall or vitreous enamel stove pipe. This arrangement allows the installer to run a short connecting section above the appliance before changing to insulated twin wall.

Do not assume that every 100mm stove outlet will fit. Nominally identical outlets can have different internal diameters, external diameters and socket depths. Therefore, check the actual connection dimensions before ordering.

Important Flue-Diameter Check

A 100mm appliance outlet does not automatically mean that a 100mm chimney would comply with the appliance instructions or UK installation requirements. In some cases, the chimney must increase to a larger diameter immediately or within the connecting section.

This component provides a 100mm to 125mm increase. However, the appliance manufacturer and chimney design must permit that change.

Never reduce the flue below the appliance manufacturer’s stated minimum diameter. An incorrect flue size can affect draught, appliance performance and the safe removal of combustion gases.

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 the chimney system.

In contrast, TWPro uses an inner flue, mineral wool insulation and a stainless-steel outer casing. The insulation helps maintain the flue temperature while reducing heat transfer to the outer wall.

Therefore, insulated twin wall can form a complete chimney route through a building or externally, subject to the correct components, clearances and installation design.

Single-wall pipe must not pass through walls, ceilings, floors, roofs or concealed spaces. The transition to the insulated chimney must take place before any building penetration and in the position required by the relevant installation instructions.

Strong Stainless-Steel Construction

The inner flue uses corrosion-resistant 316L-grade stainless steel. Meanwhile, the outer casing uses 304-grade stainless steel with a high-temperature matt-black coating.

High-density mineral wool surrounds the inner flue in the insulated section. As a result, the component helps retain heat as the flue gases enter the twin-wall chimney.

The fully welded construction also provides a strong and durable transition. Consequently, the fitting can form a reliable part of the complete chimney when installers fit, support and maintain it correctly.

Installation Guidance

First, confirm that the 100mm lower connection fits the appliance outlet or connecting pipe. Next, fit the increaser in the correct condensate-flow direction. Then connect the 125mm upper end to the compatible TWPro chimney section.

Push the TWPro joint fully together and secure it with the supplied locking band. Afterwards, check that the fitting remains straight and that the joint has fully engaged.

The appliance and connecting pipe must not carry the unsupported weight of the full chimney. Therefore, use the correct wall supports, ceiling supports, roof supports and structural components throughout the installation.

Finally, follow the appliance instructions, TWPro installation guide, Building Regulations and all other relevant standards. We recommend installation by a suitably competent person.

Which Way Up Should It Be Installed?

Install the 100mm single-wall connection at the bottom, towards the appliance. The 125mm TWPro twin-wall connection sits above it and continues into the insulated chimney.

This orientation follows the direction of the increasing transition. It also helps keep condensate and combustion deposits within the flue system when installers assemble all connecting components in the correct direction.

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

The single-wall section will normally require a larger clearance than the insulated TWPro section. Therefore, apply the correct clearance to each part of the installation and follow the greatest requirement where clearances overlap.

Does It Include a Locking Band?

Yes. The manufacturer supplies a locking band with this component. The band secures the push-fit TWPro connection at the upper end of the increaser.

Fully engage the joint before closing the locking band. In addition, check that the band remains correctly positioned and secure after installation.

Can I Mix TWPro with Another Chimney Brand?

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

Different chimney systems can use different joint depths, outer diameters, insulation types and locking methods. Therefore, components described with the same internal diameter may not connect safely.

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

Maintenance and Inspection

Inspect the adaptor and its joints during routine chimney servicing. Check the locking band, matt-black finish and single-wall connection for movement, damage or corrosion.

Also, arrange chimney sweeping at intervals that suit the appliance, fuel and frequency of use. Because the fitting changes the flue diameter, the complete system must provide suitable access for inspection and cleaning.

Replace any component that becomes damaged, distorted, heavily corroded or insecure. Furthermore, arrange a professional inspection if you notice smoke leakage, staining or a change in chimney performance.

Why Choose TWPro?

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

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

Finally, the smooth matt-black finish creates a professional appearance above both modern and traditional stoves.

Why Buy from SNH Tradecentre?

• Specialist stove, chimney and flue-system supplier
• Extensive range of matching TWPro components
• Practical 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 checking your appliance outlet, flue diameter or matching components? Call SNH Tradecentre on 01843 842727 before ordering.

Frequently Asked Questions

What sizes does this increaser connect?

It connects a 100mm single-wall pipe or compatible appliance outlet to a TWPro chimney with a 125mm internal diameter.

Does it increase the flue by 25mm?

Yes. The component increases the nominal internal flue diameter from 100mm to 125mm.

Can I connect it directly to a stove?

Yes, it can connect to some compatible 100mm appliance outlets. However, you must check the appliance spigot dimensions and manufacturer’s instructions.

Can it connect to vitreous enamel stove pipe?

Yes, the lower end can connect to compatible 100mm single-wall or vitreous enamel connecting pipe when the joint dimensions and installation design match.

Is 125mm the outside diameter of the twin-wall section?

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

Can I use it with a wood-burning stove?

It may suit a compatible wood-burning stove when the appliance manufacturer permits a 100mm outlet and a transition to a 125mm chimney. Always check the appliance instructions.

Does the increaser include a locking band?

Yes. The supplied locking band secures the upper TWPro connection.

How far must it remain from combustible materials?

The relevant insulated T600 G50 arrangement has a declared 50mm distance to combustible materials. However, the single-wall connection normally requires a greater clearance.

Can this component pass through a wall or ceiling?

The single-wall connection must not pass through walls, ceilings, floors, roofs or concealed spaces. Position the transition and insulated chimney according to the manufacturer’s instructions.

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 connections.

What is the product code?

The manufacturer’s product code is 37-100-002.