Industry Standard Update 121

BS 5440-1:2023 Chimneys, flue pipes and ventilation for gas appliances of rated input not exceeding 70kW net (1st, 2nd and 3rd family gases) – Part 1  
Date issued: 24 January 2024

This Industry Standard Update (ISU) provides an overview of the key areas of change arising from the revised British Standard 5440-1:2008 Flueing and ventilation for gas appliances of rated input not exceeding 70kW net (1st, 2nd and 3rd family gases) – Part 1: Specification for installation of gas appliances to chimneys and for maintenance of chimneys.

Introduction
During December 2023, BSI published a revised version of British Standard 5440-1:2023 Chimneys, flue pipes and ventilation for gas appliances of rated input not exceeding 70kW net (1st, 2nd and 3rd family gases) – Part 1: Design, installation, commissioning and maintenance of chimneys – Specification⁽¹⁾. The new standard came into effect on 31 December 2023 and supersedes the previous edition⁽²⁾ (March 2008), which is now withdrawn.

The following is a brief overview of the areas of significant change.

General
Legislation, normative, references and current standards have been updated throughout where necessary.

Definitions
There have been updates to some definitions, including those of communal flues and lightwells. Windows, vents and other pathways into a building are now simply referred to as openings into a building throughout the standard. It is clarified that weeps vents are not considered an opening into a building.

Courtyards
Section 5.2.3 gives updated guidance regarding chimneys/flues outlets for room-sealed or fanned-draught non room-sealed appliances terminating in lightwells and courtyards. As before, a chimney/flue can terminate a maximum of 1 metre below the top level of an enclosed space such as a light well.

For new developments or complete building refurbishments, any gas appliance shall be connected to a communal flue system. However, the chimney/flue can terminate in an inner courtyard of an existing building, provided that the narrowest dimension across the open area of the courtyard is at least that of the height of the tallest structure forming the courtyard.

Where these restrictions cannot be met, appliances may be installed in the uppermost floor of the building, or the installation treated as that of a new development or complete building refurbishment.

Existing appliances fitted in courtyards that do not meet the correct criteria may be left operational as long as satisfactory combustion can be achieved and the appliance is operating safely.

Chimney/flue routing
There is now guidance on the routing of a chimney/flue through fire compartments and other dwellings, with Section 7.1.1 stating that chimneys shall not pass through either.

Chimney/flue termination
Figure C.8 in Annex C has been expanded to include additional scenarios and distances, including the following:
• A terminal diagonally across from an opening on a different wall
• A vertical terminal from another vertical terminal
• A vertical terminal adjacent from an opening
• A vertical terminal from a wall
• A terminal facing an opening.

It is important to note that the appliance manufacturer’s instructions (MIs) may differ from the distances provided in Figure C.8. In these instances, the MIs take precedence for the installation.

Chimney/flue installation checklist
A checklist (Table D.1) has been included in Annex D to assist the engineer when confirming whether a proposed chimney/flue location is suitable. If the installation cannot meet the criteria of Table D.1, then it may be deemed unsuitable as a location, and an alternative position considered.

 Bibliography
(1) BS 5440-1:2023 Chimneys, flue pipes and ventilation for gas appliances of rated input not exceeding 70kW net (1st, 2nd and 3rd family gases) – Part 1: Design, installation, commissioning and maintenance of chimneys – Specification
(2) BS 5440-1:2008 Flueing and ventilation for gas appliances of rated input not exceeding 70kW net (1st, 2nd and 3rd family gases) – Part 1: Specification for installation of gas appliances to chimneys and for maintenance of chimneys