Potterton SIRIUS FS Installation & Servicing Instructions Manual page 38

The following table can be used as a guide when calculating the flue outlet resistance,
please refer to flue manufacturers instructions where possible :
Item
Straight (1m)
T-piece boiler outlet
90º elbow
45º elbow
Flue terminal (Zeta = 0.05 conical)
Flue terminal (H/D = 1.0, Zeta = 1.0)
Flue terminal (H/D = 0.5, Zeta = 1.5)
Flexible Flue Liner (per meter)
Item
Straight (1m)
T-piece boiler outlet
90º elbow
45º elbow
Flue terminal (Zeta = 0.05 conical)
Flue terminal (H/D = 1.0, Zeta = 1.0)
Flue terminal (H/D = 0.5, Zeta = 1.5)
Flexible Flue Liner (per meter)
Worked Example:
An FS525 boiler is to be installed on a B
1 x T-piece, 2 x 1m Straight lengths, 3 x 45
and a flue terminal. The calculation would be as follows:
The total resistance is over 250 Pa, so this 180mm flue system would not be acceptable.
Therefore a larger diameter flue system is required.
This system is still restrictive (see flue resistance table page 33) but the total resistance is
under 250 Pa, so this 200mm flue system would be acceptable.
If the same calculation was applied to a 250mm diameter flue system, the total resistance
would be 70.1 Pa, which equates to an output increase of 10kW, from a 180mm flue system.
Sirius FS
Model: FS525
Item
T-piece boiler outlet
45º Elbow
90º Elbow
1m Straight lengths
Flexible flue liner (m)
Flue Terminal (H/D 1.0, Zeta 1.0)
Total Flue Resistance (Pa)
Model: FS525
Item
T-piece boiler outlet
45º Elbow
90º Elbow
1m Straight
Flexible flue liner (m)
Flue Terminal (H/D 1.0, Zeta 1.0)
Total Flue Resistance (Pa)
Resistance Pa
Flue diameter Flue diameter
180mm
3.0
25.5
9.9
5.7
1.4
28.3
42.4
7.4
Resistance Pa
Flue diameter Flue diameter
180mm
5.0
45.3
17.6
10.1
2.5
50.4
75.6
13.7
type flue. The installation would require:
23
Elbows, 1 x 90
O
180mm Flue outlet size
Quantity Pa each
1 45.3
3 10.1
1 17.6
2
8 13.9
1 50.4
200mm Flue outlet size
Quantity Pa each
1
3
1
2
8
1
36
200mm
1.8
16.7
6.5
3.7
0.9
18.6
27.8
4.7
Flue diameter
200mm 250mm
3.0 1.0
29.7 12.2
11.6 4.7
6.6 2.7
1.7 0.7
33.0 13.5
49.6 20.3
8.9 3.5
Elbow, 8m of flexible flue liner
O
Pa Total
45.3
30.3
17.6
5.0 10.0
110.8
50.4
264.4
Pa Total
29.7 29.7
6.6 19.8
11.6 11.6
3.0 6.0
9.1 72.8
33.0 33.0
172.9
GB/IE