3.7.2 Venting options
These appliances are approved with alternative venting options: either
2-pipe direct vent or vent pipe with indoor air. With direct vent,
combustion air is piped directly to the boiler’s air intake from outdoors.
Using the indoor air alternative, air for combustion is drawn from the
indoor air surrounding the boiler.
Provided the maximum overall vent length limit is not exceeded, the
boiler may be vented through the wall, directly through the roof, or
upward using an existing, but otherwise unused, chimney as a vent
raceway.
Figure 12 Flue gas exhaust to outdoors
3.7.3 Exhaust vent material
Warnings
Condensate can cause corrosion of metal roofing components and other roofing
materials. Check with the builder or roofing contractor to ensure that materials
are resistant to acidic condensate. pH levels can be as low as 3.0.
Covering non-metallic vent pipe and fittings with thermal insulation is prohibited.
Exhaust vent material – Canada
Use PVC, CPVC, or Polypropylene (PPs) vent component systems approved under ULC-S636
Standard for Type BH Gas Venting Systems, or stainless steel Type BH venting systems
1
. ULC-
S636 components are certified as systems including pipe, fittings and cement/primer for
PVC/CPVC and must be installed in strict accordance with manufacturers' instructions. The vent
temperature is limited by the boiler controller with the use of a flue temperature sensor to ensure
the maximum temperature of the PVC venting material is not exceeded.
1
Manufacturers of stainless steel Type BH venting systems must submit their approved transition fitting to IBCfor evaluation and written
approval.
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