Product Description

TWPro 125mm Twin Wall Insulated H-Cowl Matt Black

Model: 37-125-103

Help reduce chimney downdraught in exposed locations with the TWPro 125mm Twin Wall Insulated H-Cowl. Its static H-shaped design has no moving parts. Therefore, it provides a simple and reliable option for chimneys in areas affected by strong or changing winds.

The H-Cowl also gives the flue outlet a high level of protection against direct rain and water ingress. In addition, its durable matt-black finish matches the rest of the TWPro insulated chimney system.

This terminal connects directly to compatible 125mm TWPro or KW Flue twin-wall components. However, a competent installer must confirm that an H-Cowl suits the appliance, fuel and location before installation.

Key Features

• 125mm internal flue diameter
• Static anti-downdraught terminal
• H-shaped design with no moving parts
• Suitable for exposed and high-wind locations
• Helps protect the chimney from direct rain ingress
• Durable matt-black finish
• Connects to compatible TWPro and KW Flue components
• Push-fit joint with a locking band
• Suitable for compatible solid-fuel, gas and oil appliances
• Forms part of a T600-rated insulated chimney system
• Product model: 37-125-103

TWPro 125mm H-Cowl Specification

• Download the TWPro Information Sheet
• Download the TWPro Installation Sheet
• Brand: TWPro
• Manufacturer: MI Flues
• Product type: H-Cowl chimney terminal
• Function: anti-downdraught and rain protection
• Nominal internal diameter: 125mm
• Approximate system external diameter: 175mm
• Design: static, with no moving parts
• Finish: matt black
• System connection: push fit with locking band
• Maximum system temperature class: T600
• Product model: 37-125-103

What Is Included?

• 1 x TWPro 125mm Twin Wall Insulated H-Cowl
• 1 x compatible locking band
• Finish: matt black
• Model: 37-125-103

Application

This H-Cowl provides a terminal for a correctly designed 125mm TWPro insulated chimney. It is especially useful where local wind conditions may cause downdraught or affect the safe discharge of flue gases.

The terminal can form part of a compatible chimney system serving appliances such as:

• Wood-burning stoves
• Multifuel stoves
• Other suitable solid-fuel appliances
• Compatible gas appliances
• Compatible oil-fired appliances

Always check the appliance manufacturer’s instructions before choosing a terminal. The appliance type, fuel, chimney height and surrounding buildings can all affect which cowl works best.

How Does an H-Cowl Work?

The H-shaped terminal provides several routes for flue gases to leave the chimney. As the wind changes direction, the terminal helps reduce the pressure differences that can push air back down the flue.

Because the cowl has no rotating or mechanical parts, it does not rely on bearings or wind-driven movement. As a result, it offers a simple anti-downdraught solution with fewer moving parts to maintain.

However, an H-Cowl cannot correct every chimney problem. Poor draught can also result from an undersized chimney, insufficient chimney height, air-pressure problems, nearby obstructions or a blocked flue. Therefore, an installer should identify the cause of persistent downdraught before fitting a new terminal.

Protection Against Rain and Wind

The H-Cowl helps shield the open flue from direct rainfall. In addition, its static layout makes it suitable for exposed roofs and locations that experience strong winds.

Although the terminal provides a high level of weather protection, some moisture may still enter any open-flue system during severe weather. Therefore, the complete chimney must include suitable drainage and inspection arrangements where required.

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 injected mineral wool
• Insulation density: 190kg/m³
• Joint system: push fit with locking band
• Maximum operating-temperature class: T600

These construction details describe the connected TWPro insulated chimney system. Together, the stainless-steel casings and dense mineral-wool insulation help maintain the flue temperature while protecting the outer casing.

Approvals and System Classification

• HETAS-approved chimney system
• EN 1856-1 T600 N1 W V2 L50040 G50
• EN 1856-1 T200 P1 W V2 L50040 O20
• Suitable for compatible negative-pressure applications up to T600
• Suitable for compatible positive-pressure applications up to T200

The required classification depends on the appliance, fuel and complete chimney design. Therefore, check the rating and compatibility of every component before installation.

Distance to Combustible Materials

The declared minimum distance from the TWPro insulated chimney system to combustible materials is 50mm under its T600 G50 classification.

However, the appliance or another part of the installation may require a greater clearance. Always follow the largest distance stated in the appliance and chimney-system instructions.

Installation Guidance

• Confirm that an H-Cowl suits the appliance and fuel type
• Check that the chimney provides the required height and draught
• Make sure the flue is clean and free from blockages
• Fit the cowl only to a compatible 125mm TWPro or KW Flue component
• Push the joint fully together before fitting the locking band
• Secure the supplied locking band correctly
• Keep the terminal clear of nearby walls, roofs and other obstructions
• Maintain all required distances from combustible materials
• Follow the appliance and TWPro installation instructions
• Arrange suitable access for future inspection and maintenance

The cowl forms part of a safety-critical chimney system. Therefore, a suitably competent installer should select and fit it. For solid-fuel systems, use a HETAS-registered installer where appropriate.

Compatibility

This H-Cowl fits the 125mm TWPro and corresponding KW Flue chimney systems only. Different manufacturers use their own joint profiles, dimensions and locking methods. Therefore, do not connect it to another twin-wall brand unless the manufacturer confirms compatibility in writing.

The stated 125mm measurement refers to the internal flue diameter. Since TWPro has 25mm of insulation around the inner casing, the connected twin-wall system has an external diameter of approximately 175mm.

Inspection and Maintenance

Check the terminal during routine chimney inspections. In particular, look for soot deposits, bird nesting material, storm damage or anything that could restrict the flue outlet.

Although the cowl has no moving parts, it still needs regular inspection. Furthermore, arrange chimney sweeping at intervals that suit the appliance, fuel and frequency of use.

TWPro Warranty

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

Correct product selection, installation, fuel use and maintenance may affect warranty cover. Therefore, keep your proof of purchase and follow all manufacturer instructions.

Why Choose the TWPro Twin-Wall System?

TWPro combines a corrosion-resistant 316L stainless-steel inner casing with dense mineral-wool insulation and a durable matt-black outer casing. As a result, it provides a neat insulated chimney system for a wide range of compatible heating appliances.

Its push-fit connections and locking bands also help installers form secure joints quickly. In the UK, the same system may carry the KW Flue name. However, always check the product code and joint design before combining components.

Why Buy from SNH Tradecentre?

SNH Tradecentre works closely with MI Flues, the supplier behind the TWPro chimney system. Therefore, our team can check product details, confirm availability and help you choose compatible components for your installation.

We also work closely with MI Flues to process orders quickly. As a result, we can often arrange same-day dispatch for eligible in-stock orders placed before the daily cut-off time. Delivery times and stock availability can vary, so please contact us if your order is urgent.

• Close working relationship with MI Flues
• Fast dispatch on eligible in-stock orders
• Nationwide UK delivery options
• Experienced stove and chimney product advice
• Extensive range of matching TWPro components
• Help checking product and system compatibility
• Secure online ordering
• Support before and after your purchase

If you need help choosing the correct chimney terminal, contact SNH Tradecentre before ordering. We can help you compare the H-Cowl with other compatible TWPro terminals.