Home » Blog » BS EN 1856-1 Explained: CE Marking, Fire Ratings and the New TB163 Pressure Testing Requirements

BS EN 1856-1 Explained: CE Marking, Fire Ratings and the New TB163 Pressure Testing Requirements

The specification and installation of chimney and flue systems have become increasingly complex as heating technologies evolve and building safety requirements become more demanding. While BS EN 1856-1 and BS EN 1856-2 remain the foundation of chimney system certification across Europe and the UK, recent developments such as Technical Bulletin TB163 and growing awareness of fire-rated flue systems are changing the way designers, installers and commissioning engineers approach compliance.

Understanding how CE marking, pressure classifications, fire ratings and commissioning requirements interact is essential for ensuring safe, compliant and reliable flue installations.

What Is BS EN 1856-1?

BS EN 1856-1 is the European standard that specifies the performance requirements for factory-made modular metal chimney systems. It establishes a harmonised framework for testing, classification and certification, ensuring chimney products meet strict safety and performance criteria before being placed on the market.

The standard applies to:

• Twin-wall insulated chimney systems
• Modular metal flue systems
• Chimney sections and fittings
• Supports, terminals and accessories
• System chimneys with metallic liners

It defines requirements for:

• Product performance
• Resistance to temperature
• Pressure performance
• Corrosion resistance
• Condensate resistance
• Soot fire resistance
• Product identification
• CE marking
• Factory production control

Every certified system must undergo independent testing and ongoing third-party assessment before it can be CE marked.

Why CE Marking Matters

Since the introduction of the Construction Products Regulation, CE marking has become mandatory for metal chimney systems covered by EN 1856-1 and EN 1856-2.

The CE mark demonstrates that a product has been independently tested and assessed against harmonised European standards. Certification typically includes:

• Initial type testing
• Factory Production Control (FPC)
• Ongoing surveillance audits
• Product traceability requirements

For specifiers and installers, the CE mark provides confidence that the chimney system performs in accordance with its declared characteristics.

However, an important distinction is often overlooked.

CE Marking Certifies the Product – Not the Installation

One of the most common misconceptions in the industry is the belief that CE marking automatically guarantees the performance of the completed chimney installation.

In reality, CE marking only certifies the tested product and its declared performance characteristics.

The overall system performance depends on factors such as:

• Correct design
• Installation quality
• Support arrangements
• Thermal expansion provisions
• Joint assembly
• Site modifications
• Commissioning procedures

This distinction becomes particularly important in specialist and custom-built chimney systems operating under positive pressure conditions.

Understanding Chimney Designations

Every CE-certified chimney system carries a classification code that provides essential information regarding its performance.

A typical designation may appear as:

EN 1856-1 T600 P1 W V2 L50050 G50

Each element of this code communicates a specific performance characteristic.

Temperature Classification

The temperature class identifies the maximum continuous operating temperature of the chimney.

An important detail often overlooked is that certification testing is conducted above the declared operating temperature. For example, achieving a T600 classification requires testing at temperatures approaching 700°C.

Pressure Classification

Pressure classification defines the leakage performance of the chimney system.

Common classifications include:

N1 – Negative Pressure

• Natural draught systems
• Wood-burning appliances
• Traditional chimneys

P1 – Positive Pressure

• Forced draught boilers
• Commercial heating equipment

H1 – High Pressure

• CHP systems
• Generator exhausts
• Industrial process applications

As more systems operate under positive pressure, maintaining gas-tight integrity throughout the installation becomes increasingly important.

Condensate Resistance

Modern high-efficiency appliances often produce condensate within the flue system.

The standard differentiates between:

D – Dry Operation

• No condensate resistance

W – Wet Operation

• Resistant to condensate penetration
• Suitable for condensing appliances

Corrosion Resistance

Corrosion resistance is critical for long-term durability.

Correct selection of corrosion class is essential when specifying systems for biomass, multi-fuel or industrial applications.

Soot Fire Resistance

The final section of the designation indicates whether the chimney can withstand a soot fire.

G Classification

• Tested at 1,000°C for 30 minutes
• Suitable for solid fuel applications

O Classification

• Not tested for soot fire resistance

The designation also specifies the minimum distance to combustible materials.

For example:

G50

indicates soot fire resistance with a minimum clearance of 50 mm to combustible materials.

The Growing Importance of Fire-Rated Flue Systems

One area generating increasing interest among consultants, fire engineers and building control professionals is the fire rating of flue and exhaust systems.

Many industry professionals assume that a soot fire classification automatically demonstrates fire resistance within a building compartment. This is not necessarily the case.

Soot Fire Resistance vs Fire Resistance

These are two fundamentally different tests.

A chimney classified as:

T600 P1 W V2 L50050 G50

has demonstrated resistance to an internal soot fire but has not necessarily demonstrated the ability to maintain fire compartmentation during an external building fire.

Why Fire Ratings Matter

Fire-rated chimney systems are becoming increasingly important in:

• High-rise developments
• Commercial plant rooms
• Healthcare facilities
• Data centres
• Educational buildings
• Critical infrastructure projects

As passive fire protection requirements continue to evolve, designers are increasingly required to demonstrate the fire performance of flue penetrations through walls, floors and compartment boundaries.

This is driving greater demand for independently tested fire-rated chimney and exhaust systems supported by documented evidence.

TB163: New Guidance for Specialist Flue Systems

In February 2026, Technical Bulletin TB163 introduced significant new guidance relating to the commissioning of appliances connected to custom-built or specialist chimney systems.

The bulletin recognises that modern installations increasingly rely on positive pressure operation and that system integrity must be verified after installation.

Pressure Testing Requirements

TB163 states that where a chimney or flue system is designed to operate under positive pressure conditions, pressure testing should be undertaken prior to commissioning to verify the installed system’s integrity.

This guidance reflects a growing industry focus on validating actual installed performance rather than relying solely on product certification.

Why Pressure Testing Is Important

Pressure testing provides assurance that the completed installation performs as intended and that leakage remains within acceptable limits.

This is particularly relevant for:

• Generator exhaust systems
• CHP installations
• Commercial boiler systems
• Energy centres
• Industrial process exhausts
• Data centre generator flues

Even when CE-certified components are used throughout the system, installation variables can influence overall performance.

These include:

• Joint assembly quality
• Thermal expansion provisions
• Support positioning
• Site fabrication tolerances
• Installation workmanship

Pressure testing helps identify issues before the system enters service.

V-Band Jointed Systems

TB163 also draws attention to the correct installation of V-band jointed systems.

These systems are widely used because of their speed of installation and ability to accommodate demanding operating conditions. However, their performance relies heavily on correct assembly.

Installers should always ensure:

• Correct clamp alignment
• Proper tightening procedures
• Verification of sealing components
• Inspection before commissioning
• Compliance with manufacturer instructions

Failure to follow recommended assembly procedures can compromise pressure integrity and long-term reliability.

Declaration of Performance (DoP)

Every CE-certified chimney system should be accompanied by a Declaration of Performance (DoP).

The DoP summarises the certified characteristics of the product and provides verification of compliance with the relevant harmonised standard.

Information typically includes:

• Temperature classification
• Pressure classification
• Corrosion resistance
• Condensate resistance
• Fire performance
• Structural performance
• Gas tightness
• Thermal characteristics

For consultants and installers, the DoP remains one of the most valuable technical reference documents available.

Why This Matters for Modern Projects

The industry is moving beyond simple product compliance.

Today’s projects increasingly require designers to demonstrate:

• Product certification
• System integrity
• Fire performance
• Pressure performance
• Correct commissioning procedures

As regulations continue to evolve, successful projects will rely on combining certified products with robust design, installation and verification practices.

Conclusion

BS EN 1856-1 remains the cornerstone of chimney and flue system certification, providing a clear framework for evaluating performance, safety and compliance. However, modern projects demand a broader understanding of system performance beyond CE marking alone.

The introduction of TB163 highlights the growing importance of pressure testing specialist flue systems, particularly those operating under positive pressure conditions. At the same time, increasing scrutiny of fire-rated flue systems is placing greater emphasis on compartmentation and passive fire protection requirements.

By understanding CE classifications, fire ratings, pressure testing requirements and commissioning best practices, designers and installers can ensure safer, more reliable and fully compliant chimney systems for today’s increasingly complex building environments.