Siting a flue terminal correctly – What installers need to know

Siting a flue terminal correctly will ensure that the products of combustion are safely discharged. Graham Elkins looks at the correct approach to take with every installation.

The position of a flue terminal (whether room-sealed or openflue) is very important because it will determine whether or not the products of combustion (POC) are likely to be discharged safely. The guidance
that follows is for domestic gas appliances up to 70kW net (2nd and 3rd family gases).

Terminal locations

Figure 1 and Table 1 will assist in assessing the suitability of existing flue terminal locations. For all new installations, the manufacturer’s installation instructions need to be followed.

All domestic wall-faced and wall-adjacent natural draught flue terminations are now classified as ‘At Risk’ – see the Gas Industry Unsafe Situations Procedure, Tables and Appendices.

A flue terminal guard should be fitted where the flue terminal is less than 2m above ground, above a balcony or above a flat roof where people have access.

Building regulations

The position of a flue terminal (for both open-flue and room-sealed gas appliances) needs careful consideration at the planning stage. Building regulations will also put restrictions on the location of flue terminal positions (see Figure 4).

Inspection and testing Open-flue

  • Visually inspect the flue throughout its length where possible.
  • Is the flue the correct size for the gas appliance?
  • Is the flue termination correct? (see Figure 1)
  • Is the flue material suitable and correctly jointed?
  • Is the flue unobstructed and continuous?
  • Check that the ventilation for the gas appliance is in accordance with the appliance manufacturer’s instructions.
  • Carry out a flue flow check.
  • Carry out a spillage check on the gas appliance – again in accordance with the appliance manufacturer’s instructions. Any defect should be rectified or where appropriate follow the guidance in the Gas Industry Unsafe Situations Procedure Section 10 and complete a warning notice and attach labels as necessary.

Room-sealed

  • Visually inspect the flue throughout its length where possible.

NOTE:
Where a room-sealed fanned-draught chimney/flue system is concealed within a void, refer to the guidance given in Gas Safe Register Technical Bulletin 008.

  • Check appliance case seals and any joints in the flue on extended flue systems.
  • Check the flue terminal is correct and undamaged.
  • Check the flue terminal position is correct (see Figure 2 and Table 1) and a flue terminal guard is fitted where necessary.
  • Any defect should be rectified or where appropriate follow the guidance in the Gas Industry Unsafe Situations Procedure Section 10 and complete a warning notice and attach labels as necessary.

Additional guidance

Additional guidance can be found in the following publications:

  • BS5440-1 Flueing and ventilation for gas appliances of rated input not exceeding 70kW net (1st, 2nd and 3rd family gases) Specification for installation of gas appliances to chimneys and for maintenance of chimneys.
  • Approved Document J – Combustion appliances and fuel storage systems.
Table 1. Minimum clearance for room-sealed gas appliance flue terminals.
Dimensions as indicated in Figure 2 Position of terminal Heat input (kW net) Natural draught (mm) Fanned draught (mm)
A Directly below an opening, opening window, door, air brick etc. 0 – 7 300 300
> 7 – 14 600 300
> 14 – 32 1500 300
> 32 – 70 2000 300
B Above an opening, opening window, door, air brick etc. 0 – 7 300 300
> 7 – 14 300 300
> 14 – 32 300 300
> 32 – 70 600 300
C Horizontally to an opening, opening window, door, air brick etc. 0 – 7 300 300
> 7 – 14 400 300
> 14 – 32 600 300
> 32 – 70 600 300
D Below any temperature sensitive building components e.g. plastic 0 – 70 300 75
E Below eaves 0 – 70 300 200
F Below carport roof or balconies 0 – 70 600 200
G From a vertical drain pipe or soil pipe 0 – 70 300 150
H From an internal or external corner 0 – 70 600 300
I Above ground, balcony level or roof 0 – 70 300 300
J From a surface facing a terminal 0 – 70 600 600
K From a terminal facing a terminal 0 – 70 600 1200
L From an opening in the carport into the dwelling 0 – 70 1200 1200
M Vertically from a terminal on the same wall 0 – 70 1500 1500
N Horizontally from a terminal on the same wall 0 – 70 300 300
O Above intersection with roof 0 – 70 N/A 300

To Sum Up

  • Visually inspect flue systems throughout length of flue system.
  • Carry out safety checks – e.g. flue flow check and appliance spillage check as appropriate.
  • Rectify faults identified where possible.
  • Where faults cannot be rectified, follow the guidance given in the Gas Industry Unsafe Situations Procedure Section 10.