Product Description

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

Model: 37-125-019

Add a dedicated flue-testing point to a 125mm insulated chimney with the TWPro 500mm Testing Pipe. This rigid twin-wall chimney section includes a built-in test point and removable cap, allowing a competent engineer to access the flueway during commissioning, servicing and fault diagnosis.

The test point provides a controlled entry for suitable instruments used to measure flue-gas readings or chimney draught. After testing, the engineer must refit and secure the cap before the appliance returns to normal use.

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 a practical testing point with the strong insulated construction of the TWPro chimney system.

Product at a Glance

• 125mm nominal internal flue diameter
• 500mm nominal pipe length
• Built-in flue test point
• Removable test-point cap
• Provides controlled access for flue-gas testing
• Supports chimney draught measurement
• Useful during commissioning and servicing
• Not designed as a sweeping or inspection door
• Suitable for accessible internal or external locations
• 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
• 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
• Compatible with TWPro and matching KW-branded chimney parts
• Product model: 37-125-019

What Is a Flue Testing Pipe?

A flue testing pipe is a straight chimney section with a purpose-made access point. The opening allows a suitable probe or testing instrument to enter the flueway without drilling or modifying a standard pipe.

During testing, an engineer can remove the cap and insert the required equipment. They can then take measurements while the appliance operates under the test conditions set by the appliance manufacturer.

Once the engineer completes the test, they must remove the equipment and refit the cap correctly. As a result, the chimney returns to its normal sealed operating arrangement.

What Can the Test Point Measure?

The test point may support measurements such as:

• Flue-gas composition
• Combustion readings
• Chimney draught or pressure
• Flue-gas temperature
• Appliance performance during commissioning
• Changes in readings during maintenance or fault diagnosis

The exact test depends on the appliance, fuel and engineer’s equipment. Therefore, always follow the appliance manufacturer’s commissioning and servicing instructions.

The test point provides access only. It does not measure or display readings on its own.

Why Use a Purpose-Made Testing Pipe?

A purpose-made testing pipe provides a known and resealable entry point into the flueway. Therefore, an engineer does not need to drill a hole into a standard insulated pipe.

Drilling or altering an ordinary chimney component can damage the inner casing, insulation and outer finish. It may also affect the tested system classification and product warranty.

The built-in test point offers a cleaner and more professional solution. In addition, future service engineers can use the same opening for repeat measurements.

Key Features

• Combines a straight chimney section with a dedicated test point
• Allows access without drilling the chimney
• Supports commissioning and routine servicing
• Removable cap closes the opening after testing
• Maintains a continuous 125mm internal flue route
• High-grade stainless-steel inner and outer casings
• Insulation helps maintain the flue-gas temperature
• Fully welded construction provides strength and durability
• Matt-black finish matches other TWPro components
• Push-fit joints support straightforward installation

TWPro 125mm Testing Pipe Specification

• Download the TWPro Matt Black information sheet
• View the TWPro installation diagram
• Read why we recommend TWPro twin-wall flue
• Product type: insulated twin-wall testing pipe
• Nominal internal diameter: 125mm
• Approximate outside diameter: 175mm
• Nominal pipe length: 500mm
• Test access: built-in capped test point
• 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 method: fully welded
• Joint method: push fit with locking band
• 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: 37-125-019

Important Diameter Information

The stated 125mm measurement refers to the internal flue diameter. It does not describe the pipe’s outside diameter.

TWPro places approximately 25mm of insulation around the inner flue. Therefore, the compatible pipe has an outside diameter of approximately 175mm.

Check both the internal diameter and system brand before ordering. Another manufacturer’s 125mm twin-wall pipe may use a different outside diameter or joint design.

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, follow the appliance instructions and TWPro installation guide.

Suitable Applications

This 125mm TWPro testing pipe may suit correctly specified systems serving:

• 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 instructions. Next, confirm the required chimney classification. Finally, make sure the complete route complies with Building Regulations and TWPro installation requirements.

Commissioning and Servicing

During appliance commissioning, the engineer may need to confirm that the chimney provides the correct draught and that the appliance produces acceptable combustion readings.

The built-in test point creates an accessible location for those measurements. It can also help an engineer compare readings during future servicing.

If the appliance develops a performance problem, testing may help identify poor draught, restricted airflow, combustion issues or another system fault. However, the engineer must interpret the readings alongside the appliance instructions and complete installation.

Position the Testing Pipe Carefully

Choose an accessible position where an engineer can safely remove the cap, insert testing equipment and view the instrument.

Do not place the test point behind permanent boxing, inside a wall or in another concealed location. Also, avoid positioning it where nearby surfaces prevent safe access.

The correct location may depend on the appliance manufacturer’s preferred test position. Therefore, confirm the required distance from the appliance, bends and other fittings before installation.

Keep the test point away from building penetrations so the engineer can inspect the complete fitting and cap.

The Test Cap Must Remain Fitted

Keep the test-point cap securely fitted during normal appliance operation. Only remove it when a competent engineer needs access for an approved test.

An open or incorrectly fitted test point could allow smoke, flue gases or condensate to escape. Therefore, check the cap and its sealing arrangement after every test.

Do not operate the appliance normally with the test point open. Replace a damaged or missing cap before using the system.

Not a Sweeping Door

This product provides access for a testing probe. It does not provide a full-size opening for chimney rods, brushes or soot removal.

Therefore, do not treat it as a replacement for a sweeping-door pipe, access tee or another cleaning component.

The complete chimney must still provide suitable access for inspection and sweeping. The required access arrangement will depend on the appliance, bends, offsets and chimney route.

Who Should Use the Test Point?

A competent heating or chimney engineer should carry out flue testing. The engineer must understand the appliance, fuel and required readings.

Gas-appliance testing requires an appropriately qualified Gas Safe registered engineer. Likewise, oil and solid-fuel work requires suitable competence for the appliance and installation.

Do not remove the cap simply to inspect a working chimney. Flue gases can be hot, harmful and difficult to detect.

Testing Equipment Is Not Included

The product includes the capped access point but does not include a flue-gas analyser, draught gauge, temperature probe or other test instrument.

The engineer must use calibrated equipment that suits the appliance and required measurement.

Probe sizes and methods can vary. Therefore, check that the intended equipment suits the test-point opening before installation or commissioning.

Strong Stainless-Steel Construction

The inner casing uses corrosion-resistant 316L-grade stainless steel. This surface carries smoke and 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 testing pipe matches other components in the TWPro matt-black range.

The mineral wool insulation helps retain flue heat as gases pass through the section. In addition, fully welded construction provides strength and durability.

Installation Guidance

First, plan the chimney route and choose a suitable testing position. Next, inspect the pipe and confirm that the cap and test-point assembly remain complete and undamaged.

Push each pipe connection fully into the adjoining TWPro component. Then secure every joint with the correct locking band. Finally, check that the test point remains accessible and faces a safe working area.

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

Do not rotate the installed pipe solely to improve appearance if that position makes the test point difficult or unsafe to access.

Support the Testing Pipe Correctly

The testing pipe forms part of the flueway but does not support the weight of a long chimney route.

Use the correct TWPro wall supports, base supports, ceiling supports and roof supports throughout the installation. Do not allow the test-point connection or cap to take any structural load.

Keep enough free space around the cap for safe removal and probe access. In addition, prevent other pipes, brackets or building materials from pressing against the test assembly.

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.

Measure the clearance from the closest part of the pipe or test-point assembly. Do not fill the required air gap with insulation unless the manufacturer supplies a tested component for that exact purpose.

Can It Pass Through a Wall or Ceiling?

A testing point should remain accessible for use and future inspection. Therefore, do not position the capped opening inside a wall, ceiling, floor, roof or concealed space.

Use a standard straight TWPro pipe with the correct sleeve, fire-stop, support or flashing component through the building structure where required.

Plan the route so the entire test-point assembly remains visible and accessible.

TWPro and KW Compatibility

This testing pipe fits the TWPro chimney system and compatible KW-branded versions of the same system.

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

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

Maintenance and Inspection

Inspect the test point during routine appliance and chimney maintenance. Check the cap, seal, pipe casing, joints and locking bands for damage, corrosion or movement.

Remove deposits from the test opening when necessary, but do not damage or enlarge it. Also, make sure the cap refits securely after cleaning or testing.

Replace any damaged or missing test-point component before using the appliance. Furthermore, arrange a professional inspection if you notice smoke staining, condensate leakage or movement around the cap.

Why Choose TWPro?

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

The FitSystem push-fit joint makes compatible sections straightforward to assemble, while locking bands secure the connections. Furthermore, the range includes matching pipes, test sections, bends, tees, supports, flashings and terminals.

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 choosing a test-point position or matching chimney components? Call SNH Tradecentre on 01843 842727 before ordering.

Frequently Asked Questions

What is a TWPro testing pipe?

It is an insulated chimney section with a built-in capped access point for suitable flue-gas and draught-testing equipment.

What diameter is this testing pipe?

It has a nominal internal flue diameter of 125mm and an approximate outside diameter of 175mm.

How long is the pipe?

It has a nominal overall length of 500mm. Allow for joint engagement when calculating the completed chimney height.

Does it include testing equipment?

No. It includes the capped test point only. The engineer must supply suitable calibrated testing instruments.

Can I use the opening for chimney sweeping?

No. The opening suits testing probes and does not replace a sweeping door or cleaning access component.

Can I leave the test cap open?

No. Refit and secure the cap after testing and before returning the appliance to normal operation.

Who should carry out flue testing?

A competent engineer with suitable qualifications, knowledge and calibrated equipment should complete the test.

Can I use it with a wood-burning stove?

Yes, it may suit compatible wood-burning and multifuel appliances. Check the required diameter and chimney specification in the appliance instructions.

Can I hide the test point inside a wall?

No. Keep the test point visible and accessible for commissioning, servicing and inspection.

How far must it remain from combustible materials?

The relevant T600 G50 system has a declared distance of 50mm from combustible materials. Measure from the closest part of the pipe or test assembly.

Will it fit another twin-wall chimney brand?

No compatibility should be assumed. This product fits TWPro and compatible KW components, while other systems may use different joints and outside diameters.

What is the product model?

The product model is 37-125-019.