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L
1
Fig. 15
Fig. 16
L
2
L
+ L
= 70m Max
1
2
(L
= 15m Max)
1
15m Max
7.0 Site Requirements
7.13
Flue Options
1. The Baxi Combi 80 Maxflue can be fitted with
flue systems as illustrated (Figs. 15 & 16).
2. Maximum permissible equivalent flue lengths
are:-
Vertical Roof Terminal
Separate Terminals
IMPORTANT: When installing a flue system
with separate terminals the air duct must not
exceed 15m.
3. The term Equivalent Flue Length means the
actual physical length of flue and air pipe from
boiler to terminal(s), plus the addition of a length
factor for any bends in the flue system. This
factor represents the resistance of the bend
expressed as an equivalent straight length.
4. When using 80Ø twin flue pipe each 45° bend
is equivalent to 0.25m of straight pipe. A 90°
bend is equivalent to 0.5m.
5. If an appliance is installed with separate flue
terminals the maximum equivalent length is 70m.
The flue and air duct lengths are calculated
separately, with the proviso that the air duct
cannot exceed 15m. If the air duct was only 3m
the flue duct could be up to 67m.
6. When calculating the equivalent length of a
twin pipe system connected to a single vertical
terminal the physical length is NOT that of both
pipes, but that from boiler to terminal. However,
all bends in each leg of pipe must be considered
in the calculation.
Worked Example:-
Separate Terminal Installation
Air Duct Length = 6.0m
Flue Duct Length = 15.5m
3 off - 45° Bends at 0.25m each
2 off - 90° Bends at 0.5m each
The sum is therefore:-
6.0 + 15.5 + (3 x 0.25) + (2 x 0.5) =
6.0 + 15.5 + 0.75 + 1
Total Equivalent Length = 23.25m
15m
70m
17
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