6.8.12 Gas – outlets and terminals
Outlets and terminals shall be adequately separated from combustible material and other parts of the home, and prevent the ingress of damp.
Relevant standards and guidance for gas appliances, chimneys and flue terminals:
| BS 5440-1 | Flues |
| IGE/UP/7 | Gas installation in timber framed and light steel framed buildings |
Table 3: Minimum separation distances for gas outlets (mm)
Note(s)
1. An opening here means an openable element, such as an openable window, or a fixed opening, such as an air vent. However, in addition, the outlet should not be nearer than 150mm (fanned draught) or 300mm (natural draught) to an opening into the building fabric formed for the purpose of accommodating a built-in element, such as a window frame.
2. Boundary as defined in paragraph 0.4. of Approved Document J: smaller separations to the boundary may be acceptable for appliances that have been shown to operate safely with such separations from surfaces adjacent to, or opposite, the flue outlet.
3. Should not be used.
4. This dimension may be reduced to 75mm for appliances of up to 5kW input (net).
Terminal guards should be fitted over all gas flue terminals where persons could come into contact with the terminal, or it could be damaged.
BS 5440-1 advises that, in the absence of any specific guidance from the appliance manufacturer, terminals less than 2m above ground, above a balcony, or above a flat roof which people have access to, should be guarded.
The appliance manufacturer may specify a suitable terminal guard. Generally, no part of the guard should be less than 50mm from any part of the terminal when fitted in accordance with the manufacturer’s instructions.
The guard should not have any sharp edges, which could cause injury, and openings in the guard should admit a 6mm diameter ball without force, but not a 16mm diameter ball.
Where a flue outlet is not serving a balanced flue appliance, it should be:
- situated at roof level, so that air can pass freely across it at all times
- a minimum of 600mm from openings, and at least 2,000mm where below a roof window
- fitted with a flue terminal where the flue diameter is less than 170mm (larger diameter flues should be fitted with a terminal where required by Building Regulations).
Precautions should be taken, where appropriate, to prevent damp penetration in accordance with the requirements for resistance to frost attack and weathering for solid fuel appliances (see Clauses 6.8.6.3 and 6.8.6.4).
All flues which bridge the cavity of an external wall should have a means of preventing moisture crossing the cavity, eg a moisture drip collar set in the centre of the cavity. For timber frame construction, the guidance in IGE/UP/7 should be adopted in relation to non-combustible sleeving and to maintain the integrity of the vapour control layer (VCL).
Where cavity trays and weepholes are used, they should be in line with Chapter 6.1 External masonry walls.
Figure 14: Drip collar for circular flues — cross-section
Figure 15: Drip collar plate detail for rectangular flues — cross-section
Last updated: 2nd January 2025