Direct Venting; Exhaust Vent/Air Intake Requirements; General Requirements; Combustion Air Supply - Viessmann Vitocrossal 300 CU3A Installation Instructions Manual

Direct Venting (Two-pipe System)

Exhaust Vent/Air Intake Requirements

General requirements

The Vitocrossal 300 CU3A boilers must be located in such
a way that the vent length is as short as possible and that
the vent can be routed as directly (and with as few bends)
as possible.
The minimum equivalent vent length is 3.3 ft. (1 m).
See tables on pages 35, 36 and 37 for maximum and
minimum vent lengths.
All products of combustion must be safely vented to the
outdoors. All Vitocrossal 300 CU3A boilers vent under
positive pressure and are Category IV boilers.
WARNING
Failure to ensure that all flue gases have been safely
vented to the outdoors can cause property damage,
severe personal injury, or loss of life. Flue gases may
contain deadly carbon monoxide.
Viessmann recommends that the entire vent system be
checked by a licensed professional heating contractor at
least once each year following initial installation.
The stainless steel special venting system is completely
sealed when fully assembled. Locking bands or other
method of joining are used to reinforce the joints between
pipe and fittings.
WARNING
Different manufacturers offer a number of different
joint systems and adhesives. Do not mix pipes, fittings
and/or joining methods from different manufacturers.
Failure to comply could result in leakage, potentially
causing personal injury or death.
Do not install vent pipe in a way that flue gases flow
downwards. The direction of flue gas flow must be
vertically upwards or horizontal with an upward slope.
Ensure there is no flue gas leakage into the area in which
the boiler is installed.
Check joints for leaks with the gas supply turned off and
the fan running. Use a soapy solution to check for vent leaks.
Condensate must drain from the flue pipe to the boiler.
Ensure a suitable gradient of at least 3º [approx. 2 in. per
3.3 ft. (50 mm per 1 m)].
No condensate trap is required in the vent pipe system.
If exhaust vent pipe system passes through an unheated
space, such as an attic, it must be insulated. The
insulation must have an R value sufficient to prevent
freezing of the condensate. Armaflex insulation with b in.
thickness and higher can be used.
The remaining space surrounding a chimney liner, gas
vent, or special gas vent or plastic piping installed within
a masonry, metal or factory-built flue shall not be used
to supply combustion air to the boiler. A separate
combustion air intake pipe routed back to the boiler can
be used in the remaining space if required, the boiler
venting system is approved for zero clearance, and can
be run directly beside the combustion air intake pipe.
24
CU3A Venting Systems Installation

Combustion Air Supply

The Vitocrossal boiler is suitable for sidewall, as well as
vertical venting. The Vitocrossal 300 CU3A boilers are
approved for both direct vent (sealed combustion), as well
as direct exhaust (non-sealed combustion) operation in
both horizontal and vertical arrangements. For non-sealed
combustion vent systems (i.e. room-air dependent), see
appropriate section under "Single Pipe Venting" starting
on page 43 in this manual.
The boiler must be connected to a direct vent system
in which all air for combustion is taken from the outside
atmosphere and all combustion products are discharged
safely to the outdoors. The boiler must be vented and
supplied with combustion air and exhaust vent as
described in this section. Ensure the vent and combustion
air supply comply with these instructions.
CAUTION
Do not locate boiler in areas where high dust levels or
high humidity levels are present.
CAUTION *
Do not install boiler during construction involving
drywall or heavy dust of any kind. Dust can accumulate
in the burners and cause sooting. Install boiler after all
heavy dust construction is completed.
*
Typically when the boiler is used as a temporary heat
source during the building construction phase.
Inspect all finished exhaust vent/air intake piping to ensure:
Vent/air intake pipe and fittings are of approved material.

Acceptable size, length and number of elbows on

combined vent/air intake system.
Installation is in accordance with prevailing provisions of

local codes.
Installation complies with the requirements of these

instructions, as well as the exhaust vent/air intake
supplier's instructions.
The exhaust vent and combustion air intake system and
terminations may be installed in one of the following type
terminations (2-pipe system):
1. Horizontal air intake and exhaust vent pipes.
2. Vertical air intake and exhaust vent pipes.
3. Horizontal air intake pipe and vertical exhaust vent pipe.
CAUTION
If the boiler has been exposed to high dust levels, all
burners and the heat exchanger must be cleaned prior
to use.
CAUTION
If above criteria are not properly observed and boiler
damage results, any warranty on the complete boiler
and related components will be null and void.