Trianco Contractor WM70 HE INTERNAL User, Installation, Commissioning & Servicing Instructions page 21

FIG 22
2358 & 2359 HORIZONTAL BALANCED FLUE KIT DETAILS
HOLE REQUIRED 130mm DIAMETER
THROUGH WALL TO TAKE TERMINAL
IMPORTANT:
WHEN INSTALLING THE FLUE SYSTEM, IT IS
ESSENTIAL THAT THE FLUE INCLINES SLIGHTLY
FROM THE BOILER. THIS WILL ALLOW
ANY CONDENSATION WHICH FORMS IN THE FLUE TO
RUN BACK TO THE CONDENSATE DRAIN
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