NBN Flue Standards Explained

The Designation on the Flue Part by Part

The imprint looks like a code, but each part has a meaning. Usually, the temperature class, pressure class, and corrosion class are listed in sequence. Below, you'll find the main components explained in plain language.

1. Temperature Class (T). This number shows the maximum flue gas temperature the flue can handle, for example, a lower class for a pellet stove.

2. Pressure Class (N, P, or H). This letter indicates under what pressure the flue remains tight and leak-free.

3. Condensation and Moisture (W or D). The designation W stands for wet operation with condensation, D stands for dry operation.

4. Corrosion Class (V). This class links the material to the fuel, for example, a designation like V2 for certain applications.

5. Soot Fire Resistance (G or O). The letter G means resistant to a soot fire, O means not soot fire resistant.

6. Distance to Combustible Materials. The number after G or O shows the safe distance to wood or plaster. Learn more about the distance to combustible materials for stove pipes.

These components are usually in a fixed order on a label or on the flue's casing. If you don't recognize the code, ask the seller for the meaning or for the performance declaration. This way, you avoid a flue that doesn't match your stove on paper.

A complete system carries a coherent designation, as the standard tests the components as a whole. Combining separate pieces from different brands loses that certified coherence. Therefore, manufacturers recommend staying within an approved system, from the connection to the outlet on the roof.

Checklist for Purchasing a Flue

The points below help you quickly review the imprint and the paperwork. It's best to compare them alongside your stove's manual so you don't overlook anything.

• Request the CE certificate and performance declaration

• Check if the designation is on each element

• Compare the temperature and corrosion class with your stove's manual

• See if the flue and appliance brands are compatible

• Keep the documents for your insurance and maintenance

How to Choose the Right Class for Your Appliance

Always start with your stove's manual, as it specifies the required diameter and class. A pellet stove has different requirements than a wood stove, partly due to the lower flue gas temperature and the possibility of condensation. If you're unsure about single or double-walled, read the difference between single or double-walled flue.

If you want to know which setup suits your stove, the overview on which flue you need for a pellet stove can help. If in doubt, have a professional confirm the suitability.

Besides the class, the diameter and draft height also play a significant role. A flue that is too narrow or too short causes draft problems, even if it meets the standard. Your appliance's manual usually mentions a minimum height and a recommended diameter, and these figures are as important as the class itself.

Belgium and the Netherlands: Standards and Local Regulations

The NBN EN 1856 series is a European standard, so the same CE designation applies in Belgium and the Netherlands. However, installation rules differ by region and municipality. In Belgium, local regulations play a role alongside the product standard, see the explanation on flue regulations in Belgium.

In the Netherlands, the name NBN is not used, but the CE designation on the flue remains identical. National building regulations and local rules supplement the product requirements. For a current overview, consult the flue rules in Belgium for 2026. Always check with your municipality and insurer as binding sources.

The standard and the imprint are a good starting point, but not a complete answer on their own. They show what the product can handle, while the setup, penetrations, and distances in your home determine the rest. A correct choice combines the right class with an installation that meets local regulations.