19. Air Supply
19.1 Concentric Flue
If installed with a concentric flue and as a room sealed appliance the boiler does not
require that room or internal space to have a permanent air supply.
19.2 Conventionally Flue
Safe, efficient and trouble-free operation of conventionally flued gas boilers is dependant
on the provision of an adequate supply of fresh air to the room in which the appliance is
installed. Ventilation by grilles communicating directly with the outside air or a ventilated
adjacent room is required. Where the combustion air is being taken from an adjoining
room the room itself must be ventilated to satisfy the combustion air requirement of the
appliance. Where the appliance is to be installed as a conventionally flued appliance
sufficient combustion air should also be allowed. To calculate the amount of free
combustion air required for the appliance table 9 should be used. Permanent openings
are based on the total maximum rated input.
Position ventilation grilles to avoid the risk of accidental obstruction by blocking or
flooding. BS 5540.2
Table 9 Ventilation
Vent Position
Into room or internal
space
Direct to outside air
High level
9 cm
2
per kW of input
4.5 cm
2
per kW of input
Low level
9 cm
2
per kW of input
4.5 cm
2
per kW of input
In a room or internal space
None required
None required
Conventionally flued appliance
Vent Position
Into room or internal
space
Direct to outside air
High level
9 cm
2
per kW of input
4.5 cm
2
per kW of input
Low level
18 cm
2
per kW of input
9.0 cm
2
per kW of input
Any air vent, which is to supply air to an open flued appliance, must not communicate
with any room/space containing a bath or shower or private garage.
If further guidance on ventilation is required then consult BS. 5440.2.
Detailed recommendations for air supply requirements are given in BS.5440.2. and can
also be found in the CORGI Gas
Installer Manual. The following notes are intended for general guidance only. Where
open flued appliances total input ratings exceed 7 kW the room or internal space
containing them must have an air vent of minimum effective area 4.5 cm
2
for every 1 kW
in excess of 7 kW.
19.3 Compartment Ventilation
Due to the low standing losses compartment ventilation is not required.
20. Hydraulic Requirements
