17
Multi Pass Oil Boilers
3 - GENERAL BOILER INFORMATION
Note: If the boiler is in a compartment, this must be added to the areas required for ventilation.
Minimum size of air vents required - see Figs. 9 and 10
Vent A
Vent B
Vent C
Vent D
Vent E
50/70
113 cm² (18 in²)
226 cm² (36 in²)
85 cm² (13 in²)
226 cm² (35 in²)
338 cm² (52 in²)
70/90
145 cm² (23 in²)
290 cm² (46 in²)
118 cm² (18 in²)
290 cm² (45 in²)
436 cm² (68 in²)
90/140
226 cm² (35 in²)
452 cm² (70 in²)
198 cm² (31 in²)
451 cm² (70 in²)
677 cm² (105 in²)
140/160
256 cm² (40 in²)
512 cm² (80 in²)
231 cm² (36 in²)
517 cm² (80 in²)
776 cm² (120 in²)
160/200
325 cm² (50 in²)
650 cm² (100 in²)
295 cm² (46 in²)
645 cm² (100 in²)
967 cm² (150 in²)
Fig. 10 - Combustion and ventilation air supply for conventional flue boilers
See Figs. 11 and 12
Grant boilers have high operating efficiencies. Care
must be taken to ensure the flue system is suitable for
the low flue gas temperatures.
1
An insulated flue terminating 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, will normally provide the necessary draught
of at least 8.7 N/m
2
(0.035 in wg) as measured close
to the boiler connection. If a draught of 37 N/m
2
(0.15 in wg) or more is measured, then a draught
stabiliser should be fitted in the flue.
2
The flue 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. See Fig. 13.
Conventional flue system
3.6
3
If an existing chimney is used, it must be lined with
a stainless steel liner for use with fuel oil. The top
and bottom of the annular space must be sealed and
the void filled with a suitable insulating material to
reduce cooling of the flue gases.
4
If a rigid flue is used either internally or externally, it
must be of the twin wall type with a stainless steel
inner skin suitably insulated and weather proofed.
5
The flue diameter must be as specified in
Section 1.1 for the size of boiler in question.
6
The flue must be run upwards following as near a
vertical route as possible. Horizontal runs must be
avoided and no bends should have an angle of
more than 45° from the vertical. There should be at
least 600 mm of vertical flue above the boiler
before the first bend.
