Flue System and Air Supply
Page 28
9.1 AIR
SUPPLY
A suffi cient permanent air supply to the boiler should be provided
for the following reasons:
• For proper combustion of fuel and effective discharge of
combustion products to the open air.
• For the ventilation of any confi ned space in which the boiler
is installed to prevent overheating of the boiler and any
equipment in and near the boiler.
It should be both the designer’s and installer’s concern that the air
required for these functions be introduced so as to cause as little
discomfort as possible to the building occupants and thus to offer
them the least temptation to obstruct the ventilators.
Further details may be obtained from BS 5410-1.
Open fl ue - Extract fans, where needed, should be in accordance
with Section 5.4.7 in BS 5410-1.
All ventilation areas given are for domestic applications and relate
to the full output rating of the boiler.
For installations in older dwellings (constructed prior to the
introduction of Approved Document L1A 2006) the fi rst 5 kW of
output can be ignored. For all other cases refer to BS 5410-2.
BOILER IN
ROOM
Room sealed balanced flue
no ventilation required to room
BOILER IN
COMP AR TMENT
Room sealed balanced flue
compartment ventilated from room
Room sealed balanced flue
compartment ventilated from outside
B
B
A
A
Figure 9-1:
Air supply for room sealed balanced fl ue boilers
BOILER IN
ROOM
Conventional open flue
C
BOILER IN
COMP AR TMENT
Conventional open flue
compartment ventilated from room
Conventional open flue
compartment ventilated from outside
C
C
D
D
E
Figure 9-2:
Air supply for conventional fl ue boilers
9.2
CONVENTIONAL FLUE SYSTEMS
Grant condensing boilers have high operating effi ciencies and low
fl ue gas temperatures. Care must be taken to ensure the fl ue system
is suitable for the very low fl ue gas temperatures and condensate in
the fl ue gases.
Suitable conventional fl ue systems are available from Grant Ireland.
The fl ue must terminate in a down draught free area, i.e. at least
600 mm above the point of exit through the roof or preferably
above the ridge level.
The condensate may be allowed to run back into the boiler. A
condensate drain at the base of the fl ue system is not required.
The high level fl ue terminal must be at least 600 mm from any
opening into the building, and 600 mm above any vertical structure
or wall less than a horizontal distance of 750 mm from the terminal.
If an existing chimney is to be used, it must be lined with a smooth
bore stainless steel liner suitable for use with oil fi red condensing
boilers. The top and bottom of the annular space must be sealed.
Grant recommends the use of the Grant ‘Orange’ fl ue system,
specifi cally designed for the Vortex range of condensing boilers this
fl exible liner should not be visible from outside the chimney stack..
The internal fl ue and liner diameter for all models up to 46 kW
output must be 100 mm (4 in) and for the 46/70 models 125 mm
(5 in).
The maximum vertical height (from the top of the boiler to the
terminal) for the ‘Orange’ system is 19 metres.
Table 9-3:
Ventilation areas
Output
15/26 kW
26/36 kW
36/46 kW
46/70 kW
Area
cm
²
in
²
cm
²
in
²
cm
²
in
²
cm
²
in
²
Vent A
143
23
198
31
253
40
385
60
Vent B
286
46
396
62
506
80
770
120
Vent C
143
23
198
31
253
40
385
60
Vent D
286
46
396
62
506
80
770
120
Vent E
429
69
594
93
759
120
1,155
180
9 FLUE SYSTEM AND AIR SUPPLY SYSTEM
For a boiler fi tted in a compartment, which is
ventilated as shown, no additional allowance
is necessary.
NOTE
Under no circumstances can Grant Vortex
boilers be installed with existing fl ue systems.
Only fl ue systems and components suitable for
wet fl ues should be used.
Failure to install the correct type of fl ue system
will invalidate the guarantee.
NOTE
