Product Description

TWPro 125mm Twin Wall 500mm Pipe with Sweeping Door Matt Black

Model: 37-125-023

Add a practical cleaning point to your chimney with the TWPro 125mm Twin Wall 500mm Pipe with Sweeping Door. This insulated chimney section includes built-in access to the inner flue, which helps make inspection and sweeping easier.

The pipe has an inner access door and a separate outer cover. Easy-release clamps hold the doors securely in place. Therefore, a chimney sweep can reach the flue without taking apart the surrounding chimney sections.

Important: This is an N1 negative-pressure component for non-condensing installations. It is not suitable for positive-pressure or condensing flue systems. Always ask a suitably competent installer to confirm compatibility before ordering.

Key Features

• 125mm internal flue diameter
• 500mm nominal pipe length
• Built-in sweeping and inspection access
• Separate inner access door and outer cover
• Easy-access locking clamps
• Designed for N1 negative-pressure systems
• Suitable for non-condensing installations only
• Matt-black powder-coated finish
• 316L-grade stainless-steel inner casing
• 304-grade stainless-steel outer casing
• 25mm high-density mineral-wool insulation
• Push-fit joint with locking band
• Suitable for compatible TWPro and KW Flue systems
• Product model: 37-125-023

TWPro 125mm 500mm Access Pipe Specification

Read: Why We Think TWPro Twin-Wall Flue Is the Best

• Download the TWPro Information Sheet
• Download the TWPro Installation Sheet
• Brand: TWPro
• Product type: insulated access and sweeping pipe
• Nominal internal diameter: 125mm
• Approximate external diameter: 175mm
• Nominal length: 500mm
• Pressure class: N1
• Operating condition: non-condensing
• Inner casing: 0.4mm 316L-grade stainless steel
• Outer casing: 0.4mm 304-grade stainless steel
• Outer finish: matt-black powder coating
• Insulation: 25mm high-density mineral wool
• Joint method: push fit with locking band
• Maximum operating-temperature class: T600
• Declared distance to combustible materials: 50mm
• Product model: 37-125-023

What Is Included?

• 1 x TWPro 125mm Twin Wall 500mm Access Pipe
• 1 x inner sweeping-access door
• 1 x outer cover door
• Access-door locking clamps
• Matt-black finish
• Model: 37-125-023

Application

This 500mm access pipe forms part of a correctly designed TWPro insulated chimney. Installers can use it to provide a convenient sweeping and inspection point within a suitable N1, non-condensing flue system.

Subject to the appliance and chimney-system instructions, suitable applications may include:

• Wood-burning stoves
• Multifuel stoves
• Other compatible solid-fuel appliances
• Suitable non-condensing gas appliances
• Suitable non-condensing oil-fired appliances

Always check the appliance instructions before installation. In particular, confirm the required flue diameter, pressure class, temperature rating and operating conditions.

Built-In Sweeping Access

The built-in access point allows a chimney sweep or installer to reach the inner flue. As a result, they can inspect and clean the chimney without separating the surrounding pipe sections.

The pipe has two covers. First, the outer door provides access through the insulated casing. Then, the inner door opens into the flueway. Locking clamps help keep both covers secure during normal use.

Position the pipe where both doors remain easy to reach. Do not hide the access point behind permanent boxing, wall finishes or fitted furniture.

What Does N1 Mean?

N1 identifies this product as a component for suitable negative-pressure chimney systems. In these systems, the natural chimney draught carries the combustion gases upwards through the flue.

Because this component includes an access door, it is not suitable for P1 positive-pressure operation. Therefore, do not use it with an appliance or chimney design that requires a pressure-tight P1 component.

Non-Condensing Installations Only

This access pipe is designed for non-condensing flue applications. Do not install it where the appliance or chimney design may create regular condensate inside the flue.

Some gas and oil appliances operate under condensing or positive-pressure conditions. Therefore, always check the appliance manufacturer’s instructions and ask the system designer to confirm that this N1 access pipe is suitable.

Where Should the Access Pipe Be Installed?

Install the access pipe in a position that gives safe and practical access for future sweeping. For example, it may provide a cleaning point where the chimney route would otherwise be difficult to reach.

Keep enough clear space in front of the access doors to release the clamps and remove the covers. In addition, make sure the surrounding chimney remains correctly supported and does not place weight on the appliance outlet.

TWPro System Construction

• Inner casing: 0.4mm 316L-grade stainless steel
• Outer casing: 0.4mm 304-grade stainless steel
• Outer finish: matt-black powder coating
• Insulation: 25mm high-density mineral wool
• Joint system: push fit with locking band
• Maximum operating-temperature class: T600

The 316L stainless-steel inner casing provides a durable route for the flue gases. Meanwhile, the mineral-wool insulation helps retain heat inside the chimney. The matt-black outer casing then provides a neat finish for visible installations.

Approvals and Classification

• Forms part of a HETAS-approved chimney system
• TWPro system classification: EN 1856-1 T600 N1 W V2 L50040 G50
• TWPro system classification: EN 1856-1 T200 P1 W V2 L50040 O20
• This access-door component is for N1 negative-pressure use only
• This component is intended for non-condensing installations

TWPro carries system classifications for different operating conditions. However, this particular access-door pipe has an N1 pressure rating. Therefore, do not treat it as a P1 component simply because other TWPro products may carry a P1 classification.

Distance to Combustible Materials

Maintain at least 50mm between the TWPro insulated chimney and combustible materials when it operates under its T600 G50 classification.

However, another part of the installation may need a greater distance. For this reason, always follow the largest clearance stated in the appliance and chimney instructions.

Installation Guidance

• Confirm that the appliance uses an N1 negative-pressure flue system
• Confirm that the installation is non-condensing
• Choose a position that remains easy to reach for sweeping
• Keep enough space to remove both access covers
• Fit the pipe in the correct flue-gas direction
• Push each joint fully together
• Fit the required locking band at each joint
• Support the chimney at the intervals stated by the manufacturer
• Maintain the required distance from combustible materials
• Use the correct firestop and support components at building penetrations
• Follow the appliance and TWPro installation instructions

A suitably competent installer should design and fit the complete chimney. For solid-fuel installations, use a HETAS-registered installer where appropriate.

Compatibility

This component fits the 125mm TWPro and corresponding KW Flue systems only. Other chimney brands may use different joint sizes and locking methods. Therefore, do not mix components unless the manufacturer confirms compatibility in writing.

The stated 125mm measurement refers to the internal flue diameter. Because the pipe contains 25mm of insulation around the inner casing, its external diameter is approximately 175mm.

Inspection and Maintenance

Check the inner door, outer cover and locking clamps during routine chimney maintenance. Both doors should remain secure, correctly fitted and free from damage.

Arrange regular chimney sweeping based on the appliance, fuel and frequency of use. Also replace any component that becomes damaged, distorted, heavily corroded or insecure.

After sweeping, make sure the installer or chimney sweep refits both access covers correctly before the appliance returns to use.

TWPro Warranty

• 25-year system warranty, subject to the manufacturer’s conditions
• 2-year warranty on the painted finish

Product selection, installation, fuel choice and maintenance may affect warranty cover. Therefore, follow the manufacturer’s instructions and keep your proof of purchase.

Why Choose TWPro?

TWPro combines a durable 316L stainless-steel inner casing with 25mm mineral-wool insulation and a matt-black outer casing. In addition, its push-fit joints and locking bands help installers build a neat and secure chimney route.

This access pipe also adds a practical cleaning point. Therefore, it can make future inspection and chimney sweeping easier when the system design requires accessible flueway entry.

Why Buy from SNH Tradecentre?

• Specialist supplier of chimney, flue and stove products
• Wide range of matching 125mm TWPro components
• Practical advice before and after your purchase
• Close working relationship with MI Flues
• Fast nationwide UK delivery options
• Secure online ordering

SNH Tradecentre works closely with MI Flues to process TWPro orders quickly. As a result, we can often arrange same-day dispatch on eligible in-stock orders placed before the relevant cut-off time. Stock levels, order size and delivery location may affect availability, so contact us if your order is urgent.

Need help checking whether this N1 access pipe suits your chimney? Call the SNH Tradecentre team on 01843 842727 before ordering.

Frequently Asked Questions

What is this TWPro access pipe used for?

It adds a direct sweeping and inspection point to a compatible 125mm TWPro twin-wall chimney. The built-in doors allow access to the inner flueway.

How long is the pipe?

The pipe has a nominal overall length of 500mm. Check the manufacturer’s dimensions when calculating the final installed chimney height.

What diameter is the pipe?

The pipe has a nominal internal flue diameter of 125mm, which is approximately 5 inches. Its external diameter is approximately 175mm.

What does non-condensing mean?

It means the component is not designed for a chimney where regular condensate forms inside the flue. Always confirm the appliance’s operating conditions before installation.

Can I use it on a positive-pressure system?

No. This access-door pipe has an N1 negative-pressure rating. Do not use it where the appliance or flue design requires a P1 positive-pressure component.

Can it be used with a wood-burning stove?

Yes, it may form part of a suitable N1, non-condensing chimney for a compatible wood-burning stove. Always follow the appliance manufacturer’s instructions.

Can it be used with gas or oil appliances?

Only when the appliance uses a compatible N1, non-condensing chimney arrangement. Many modern gas and oil appliances have different pressure or condensate requirements, so check before ordering.

Does the sweeping door need to remain accessible?

Yes. Leave enough space to release the clamps and remove both covers. Do not conceal the door behind permanent building finishes.

Does this pipe fit other twin-wall chimney brands?

No. It is designed for compatible 125mm TWPro and corresponding KW Flue components. Do not connect it to another brand unless written approval confirms compatibility.

How far must the pipe remain from combustible materials?

The declared distance is 50mm under the T600 G50 classification. Follow any greater clearance required elsewhere in the installation.