• Description

Location of outlets from flues serving gas appliances

The correct positioning of gas flue outlets are important if the flue is to work properly.

Distance Location Minimum separation distances for terminals (mm)
Balanced flue Open flue
Natural draught Fanned draught Natural draught Fanned draught
A Below an opening (1) Appliance rated
heat input (net)
0 – 7 kW:
>7 – 14 kW:
>14 to 32 kW:
> 32kW:


300 Not to be used 300
B Above an opening (1) 0 – 32 kW:
300 Not to be used 300
C Horizontally to an opening (1) 0 – 7 kW:
>7 – 14kW:
> 14kW:
Not to be used 300
D Below gutters, soil pipes or drains. 300 75 Not to be used 75
E Below eaves 300 200 Not to be used 200
F Below balcony or car park roof 600 200 Not to be used 200
G From a vertical drain or soil pipe 300 150 (3) Not to be used 150
H From an internal or external corner
or to a boundary alongside the
terminal (2)
600 300 Not to be used 200
I Above ground, roof or balcony
300 300 Not to be used 300
J Above ground, roof or balcony
600 600 Not to be used 600
K From a terminal facing the terminal 600 1200 Not to be used 1200
L From an opening in the car port
into a building
1200 1200 Not to be used 1200
M Vertically from a terminal on the
same wall
1500 1500 Not to be used 1500
N Horizontally from a terminal on the
same wall
300 300 Not to be used 300
O From the wall on which the
terminal is mounted
Not applicable Not applicable Not applicable 50
P From a vertical structure on the
Not applicable Not applicable 1500 if a ridge
terminal. For any
other terminal as
per BE 5440 – 1:
Not applicable
Q Above the highest point of
intersection with the roof
Not applicable Site in
accordance with
Site in accordance
with BS 5440 – 1:
  1. An opening here means an openable element, such as an openable window, or a fixed opening such as a vent. However, in addition, the outlet shall not be nearer than 150 mm (fanned draught) or 300 mm (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. 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. This dimension may be reduced to 75 mm for an appliance with an input (net) not greater than 5 kW.
Location of outlets near roof windows or openings (from flues serving gas appliances)

gas flue outlet at roof level

Please check with your local building control department before using information contained in this page to ensure that they comply with your local building codes.