Flexible Flue Liner in Existing Chimney

How to Install a Flexible Pipe in the Chimney

1. First, have the chimney inspected and swept to ensure a clear, straight flue.

2. Determine the correct diameter based on the stove connection and the manufacturer's manual.

3. Insert the flexible stainless steel pipe from the top of the chimney and lower it to the bottom.

4. Connect the pipe at the bottom with a T-piece and a condensate trap.

5. Finish the top with a suitable draft cap and seal the passage neatly.

6. Have the installation checked and request a certificate for your insurance.

Checklist: Is Your Chimney Suitable for a Flexible Liner?

Before purchasing a liner, check the key points. If all are in order, a flexible liner is usually a suitable and durable solution.

• The chimney is sufficiently straight, without sharp bends.

• The internal size is larger than the chosen pipe diameter, with room for insulation.

• The masonry is sound, without cracks or loose joints.

• The chimney extends high enough above the ridge or roof edge.

• There is an inspection hatch or other access for maintenance.

Material, Diameter, and Condensation

Choose a flexible pipe in stainless steel 316, as this steel is resistant to the acidic condensation from pellets. Cheaper grades rust faster and lose their density, requiring work again after a few years.

A flexible liner is available as double-walled or as a single-walled pipe that you lower into the chimney. The single-walled version is flexible and follows slight bends in the masonry. For a pellet stove, a smooth inner wall is important as it keeps resistance low and cleaning easy. Ask your supplier for the liner's quality labels before ordering.

The diameter follows your stove's connection, usually 80 mm and sometimes 100 or 150 mm. If unsure about the size, first read which stove pipe diameter you need.

Pellet smoke is relatively cool, causing condensation to form more quickly in the flue. A condensate trap at the bottom collects this moisture and drains it in a controlled manner. More explanation can be found at why condensate traps are important for pellet stoves.

In a cold or external wall chimney, it's best to insulate the liner to keep the flue gases warm and maintain the draft. In a well-enclosed internal chimney, the space between the pipe and masonry is often insulating enough. Your installer will assess this on-site.

Have the Chimney Inspected First in Belgium and the Netherlands

Always have the existing chimney inspected before installing a liner. Both in Belgium and the Netherlands, there are regulations regarding flue gas discharge, although the details vary by region and municipality.

In Belgium, installers often refer to the NBN standards for flue gas discharge. Your insurer may also require a valid certificate. Which flue is suitable for your appliance can be found in which flue you need for a pellet stove.

In the Netherlands, the approach varies by municipality and is often determined by the Building Decree along with your insurer's requirements. A liner that is correctly installed and inspected is considered the safest option for an old chimney in both countries.

If you're unsure whether a liner is sufficient or if you need to connect the stove differently, see how to connect a pellet stove to an existing chimney and read about when a flexible stainless steel liner is needed in an existing chimney. Always consult a professional if in doubt, as a wrong assessment can cost you draft, fuel, and safety.

Want to be sure if your chimney is suitable for a flexible stainless steel liner? We inspect the flue and install a suitable flue if necessary. Request a free quote or advice and you'll know exactly where you stand.