Potterton Promax SL Series Installation & Service Instructions Manual page 40

Fig. C
4. It is possible to reduce or increase (with the addition of extensions) the length of either or both the 70/110 concentric and 70Ø
exhaust.
5. Standard concentric flue extension kits may be added between the boiler elbow and the terminal assembly.
6. The minimum length of the concentric flue is 100mm when measured from the edge of the boiler flue elbow. There is a further
45mm engagement into the elbow.
IMPORTANT: The maximum equivalent length of concentric flue
is:­ 4 metres
Additional elbows may be fitted in the concentric flue, but the
equivalent length must be reduced by 1 metre (93° elbow) or 0.5
metres (45° elbow).
7. 70Ø 1 metre extensions (including support bracket), and additional 93° & 45° elbows are available. Any additional 93° & 45°
elbows must be accounted for when calculating flue lengths. 70Ø 93° elbows are equivalent to 3.5 metres of straight length and
45° elbows to 1 metre.
NOTE: Permitted positions of the plume outlet relative to doors,
windows etc. are the same as for conventional concentric flues as
detailed in the main Installation & Servicing Instructions and
BS5440 Pt. 1.
It is NOT necessary to fit a terminal guard over the air inlet or the
plume outlet.