Product Description

125mm Rigid to Flexible Flue Liner Adaptor – 20-125-MAE

The 125mm Rigid to Flexible Flue Liner Adaptor connects a compatible 125mm single-wall connecting flue pipe to a 125mm flexible chimney liner at the base of a masonry chimney.

This MI-FLEX adaptor provides the transition between the visible rigid pipe below and the flexible liner inside the chimney. Therefore, it suits compatible wood-burning, multi-fuel, gas and oil appliance installations.

The adaptor uses strong 316L stainless steel to resist heat and corrosion. In addition, its integral drain hole helps direct condensate back into the flue system rather than allowing it to collect around the connection.

125mm Rigid-to-Flex Adaptor Features

• Rigid connecting pipe to flexible liner adaptor
• Manufacturer part number: 20-125-MAE
• 125mm / 5-inch nominal diameter
• Connects compatible 125mm single-wall pipe to 125mm flexible liner
• Designed for use at the base of a masonry chimney
• Compatible with suitable MI-FLEX 316 liners
• Compatible with suitable MI-FLEX 904 liners
• Manufactured from 316L stainless steel
• Approximately 0.6mm material thickness
• Integral condensate drain hole
• Maximum continuous temperature class: 600°C
• Suitable for compatible wood-burning appliances
• Suitable for compatible smokeless-fuel appliances
• Suitable for compatible gas and oil appliances
• Designed to support a secure, gas-tight transition
• Suitable for installations designed to Approved Document J

Technical Specification

• Brand: MI-FLEX
• Manufacturer: MI-Flues
• Part number: 20-125-MAE
• Product type: Rigid-to-flexible flue adaptor
• Nominal rigid connection: 125mm / 5 inches
• Nominal liner connection: 125mm / 5 inches
• Material: 316L stainless steel
• Material thickness: Approximately 0.6mm
• Temperature classification: T600
• Maximum continuous temperature class: 600°C
• Compatible liner grades: MI-FLEX 316 and 904, subject to system approval
• Suitable fuels: Wood, smokeless fuel, gas and oil
• Installation location: Base of an existing masonry chimney
• GTIN / EAN: 8435265435731

What Does a Rigid-to-Flex Adaptor Do?

A stove or heating appliance normally connects to a rigid single-wall pipe within the room. Meanwhile, a flexible liner runs inside the existing masonry chimney.

This adaptor joins those two parts at the base of the chimney. As a result, the combustion gases can pass from the connecting pipe into the correctly fitted flexible liner.

However, the adaptor only forms one part of the chimney system. The installation may also need a register plate, liner support, top plate, clamp, terminal, cowl and suitable access for sweeping.

Compatible Rigid Flue Pipe

The lower connection can suit approved 125mm single-wall connecting systems. Depending on the complete installation, these may include compatible vitreous enamel or stainless steel connecting pipes.

However, products from different manufacturers may use different socket sizes and joint designs. Therefore, do not assume that every item labelled 125mm will connect correctly.

Before ordering, confirm compatibility between the adaptor, rigid pipe and flexible liner. The installer should also check every manufacturer’s current fitting instructions.

Compatible Flexible Flue Liner

This adaptor is designed for compatible 125mm MI-FLEX chimney liner, including suitable 316 and 904 grades. However, the correct grade depends on the fuel, appliance and expected use.

For example, 904-grade liner may offer greater resistance in demanding solid-fuel applications. Nevertheless, an installer must select the liner from the appliance instructions, fuel type and complete chimney design.

Suitable Appliances and Fuels

• Compatible wood-burning stoves
• Compatible multi-fuel stoves
• Suitable smokeless-fuel appliances
• Suitable gas appliances
• Suitable oil-fired appliances
• Appliances approved for a 125mm flue system

The selected appliance must permit a 125mm flue. Furthermore, the chimney must provide the correct flue area, height, draught and terminal arrangement for that appliance.

Important Flexible Liner Restrictions

A flexible flue liner must remain fully enclosed inside a suitable existing masonry chimney. It must not run exposed within a room, loft or purpose-built timber or plasterboard enclosure.

The transition from rigid pipe to flexible liner should take place within the confines of the masonry chimney. Therefore, flexible liner should not remain visible below the chimney opening.

A flexible liner does not create a complete chimney by itself. The original chimney must remain structurally suitable and provide the required fire protection.

Gas-Tight Flue Connections

The installer must secure the flexible liner above and the rigid pipe below in accordance with the MI-FLEX instructions. Every connection must remain mechanically secure and gas-tight throughout normal use.

The approved jointing method may include suitable fire cement, ceramic rope, high-temperature sealant, tape or system-specific clamps. However, the installer must only use materials permitted by the product and appliance manufacturers.

Do not rely on an unsupported push-fit connection. Heat, cleaning and normal movement could loosen an incorrectly secured joint.

Integral Condensate Drain Hole

The adaptor includes an integral drain hole designed to help keep condensate within the flue route. This feature reduces the chance of moisture collecting around the external connection.

However, correct component orientation remains essential. The installer must follow the gas-flow arrows on the flexible liner and the fitting direction shown in the MI-FLEX instructions.

Preparing the Chimney

A competent person should inspect and sweep the chimney before installing a new liner. They should also check its route, dimensions, condition and suitability for the proposed appliance.

In addition, the installer should confirm that the selected liner can pass through the complete chimney. Bends, offsets, damaged masonry and old obstructions may prevent safe installation.

The chimney pot, stack and terminal must also remain suitable. Any repair or removal work at roof level requires safe access and suitable working-at-height precautions.

Flexible Liner Installation Direction

A flexible liner normally enters the chimney from the top. The arrows printed on the liner must point upwards in the direction of the flue gases.

Do not reverse the liner. An incorrect orientation can expose its internal structure to condensate and deposits in a way the manufacturer did not intend.

A suitable nose cone and pulling rope may help guide the liner through the chimney. However, trained people should manage the work from safe positions at both the top and bottom.

Why Choose a 316L Stainless Steel Adaptor?

316L stainless steel provides useful resistance to heat, moisture and corrosive combustion products. Therefore, it suits the transition area between rigid pipe and flexible chimney liner.

Its stainless construction also avoids placing a mild-steel connector directly within this demanding part of the chimney. However, correct installation and regular maintenance remain essential for long service life.

Why Buy from SNH Tradecentre?

• Competitive prices: We aim to offer excellent value across our flue-liner range.
• Collection available: Collect from our Birchington trade counter when the adaptor is in stock.
• Delivery options: We offer convenient delivery throughout eligible UK areas.
• Helpful advice: Our team can help you compare common liner sizes and bottom fittings.
• Clear product information: We provide useful compatibility and installation details.
• Genuine products: Buy from an established plumbing and heating merchant.
• Trade and public welcome: We supply installers, businesses, landlords and homeowners.
• Independent merchant: SNH Tradecentre is based in Birchington, Kent.

Need Help Choosing a Flue Adaptor?

Not sure whether this adaptor will connect your pipe and liner? Call SNH Tradecentre on 01843 842727. Please have the appliance model, rigid pipe system and flexible liner details available.

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Installation Requirements

A competent installer should design and fit the complete flue system. For solid-fuel appliances, use a HETAS-registered installer or notify Local Authority Building Control where required.

The installation must follow the appliance instructions, MI-FLEX guidance and current Building Regulations. In England and Wales, the work must also meet the applicable requirements of Approved Document J.

The installer must check chimney condition, liner grade, flue diameter, ventilation, clearances, supports, terminal position and sweeping access before completing the work.

A carbon monoxide alarm must be installed where current regulations require one. However, an alarm does not replace correct installation, maintenance or chimney sweeping.

Inspection and Maintenance

The chimney system must provide suitable access for inspection and sweeping. Therefore, the connecting flue may need an access door near its base or at changes of direction.

A competent person should inspect and clean the system regularly. Solid-fuel chimneys may require sweeping more than once a year, depending on the fuel, appliance and frequency of use.

Do not use chemical chimney cleaners or mild-steel sweeping tools on stainless steel components unless the manufacturer expressly allows them. Instead, use suitable equipment that will not contaminate or damage the stainless steel.

Frequently Asked Questions

What does this flue adaptor connect?

It connects compatible 125mm rigid single-wall flue pipe to compatible 125mm MI-FLEX flexible chimney liner at the base of a masonry chimney.

What size is the adaptor?

Both connections have a nominal diameter of 125mm, commonly described as 5 inches.

Is the adaptor made from stainless steel?

Yes. The adaptor uses approximately 0.6mm thick 316L stainless steel for heat and corrosion resistance.

Can I use it with 904-grade liner?

It can connect to a suitable MI-FLEX 904 liner. However, confirm the liner, adaptor and rigid pipe compatibility before ordering.

Will it connect to every 125mm stove pipe?

Not necessarily. Different flue systems may have different socket and spigot designs. Therefore, the installer must confirm actual compatibility.

Where should the adaptor be installed?

The adaptor normally sits at the base of the chimney where the rigid connecting pipe changes to flexible liner. The flexible liner must remain inside the masonry chimney.

Can flexible liner remain exposed below the chimney?

No. Flexible liner should remain enclosed within the existing masonry chimney. A suitable rigid connecting flue must serve the visible section below it.

Which way should the liner arrows point?

The arrows on the flexible liner must point upwards in the direction of the flue gases and chimney terminal.

What is the maximum temperature rating?

The adaptor has a maximum continuous temperature class of 600°C, commonly described as T600.

Does the adaptor support the liner?

No. The complete installation requires suitable liner supports and top fittings. Do not use this bottom adaptor as the liner’s only support.

Who should install the adaptor?

A competent installer should fit it as part of a designed chimney system. For solid-fuel work, a HETAS-registered installer can complete and certify the installation where the scheme applies.

Order the 125mm Rigid-to-Flex Adaptor

Choose the 125mm MI-FLEX Rigid to Flexible Flue Liner Adaptor 20-125-MAE to connect compatible single-wall pipe to a 125mm flexible liner at the base of a masonry chimney.

Before ordering, confirm the appliance requirements, liner grade, rigid pipe system and actual connection sizes with your installer.

Manufacturers may update specifications and installation guidance. Therefore, check the latest MI-FLEX instructions and confirm suitability with a competent installer before ordering.