Combustion Air Supply - Viessmann Vitocrossal 300 CU3A Installation Instructions Manual

CU3A Venting Systems Installation

Combustion Air Supply

The boiler used in this application requires fresh air for
safe operation and must be installed in a mechanical room
where there are provisions for adequate combustion and
ventilation air.
There are no provisions available on the Vitocrossal 300
CU3A boiler to interlock it with an external combustion air
blower.
The Vitocrossal 300 CU3A boiler is suitable for vertical
venting using flexible venting system material. The
Vitocrossal 300 CU3A boilers are approved for direct
exhaust (non-sealed combustion) operation in vertical
arrangements only.
Provisions for combustion and ventilation air must be
made in accordance with CAN/CSA-B149.1 or .2 Natural
Gas Installation Codes (for installations in Canada) or in
accordance with sections for Combustion and Ventilation
Air, of the National Fuel Gas Code, ANSI Z223.1 or
applicable provisions of local codes (for installations in
the U.S.A.) Always use the latest edition of the applicable
standard.
Follow local codes to properly isolate the vent pipe when
passing through floors, ceilings and roof.
Whenever possible, install boiler near an outside wall so
that it is easy to duct fresh air directly to the boiler area.
Refer to national codes for duct sizing. Round ducts may
be used.
The boiler must be vented and supplied with combustion
air and exhaust vents as described in this section. Ensure
the vent and combustion air supply comply with these
instructions.
WARNING
Failure to provide an adequate supply of fresh combustion
air can cause poisonous flue gases to enter living space,
which can cause severe personal injury or loss of life.
The boiler location should never be under negative
pressure. Exhaust fans, attic fans, or dryer fans may
cause air to be exhausted at a rate higher than the air can
enter the structure for safe combustion. Corrective action
must be taken to ensure enough air is available. Never
cover the boiler or store debris or other materials near
the boiler, or in any way block the flow of adequate fresh
combustion air to the boiler.
f boiler is installed in a confined space (a space with a
volume of less than 50 cubic feet per 1000 Btu/h of gas
input for all fuel burning equipment) or building layout
is unusually tight, adequate air for combustion must be
provided by two openings: one located about 6 in. (152 mm)
below the ceiling, the other about 6 in. (152 mm) above
the floor. When communicating directly with the outside,
each opening must have a minimum free area of one square
inch per 2000 Btu/h of gas input. When all combustion air
is provided by openings in doors, etc. to adjoining spaces
having adequate infiltration, each opening must have a
minimum free area of one square inch per 1000 Btu/h of
gas input, but not less than 100 in .
2
Single Pipe Venting (Room Air Dependent)
You must know the free area of louvers used to cover
up the combustion and ventilation openings in closet
installations. If you do not know the free area, assume
20% for wood louvers and 60 - 75% free area for metal
louvers. When using louvers, the openings have to be
made larger. For example, a free 14 in. x 6 in. (356 mm x
152 mm) opening becomes a 14 in. x 10 in. (356 mm x
254 mm) opening for a grill containing metal louvers.
CAUTION
Do not store chemicals containing chlorine or other
corrosive materials near the boiler, such as bleach,
cleaning solvents, detergents, acids, hair spray,
spray cans, paint thinners, paint, water softener salt,
perchloroethylene, or carbon tetra chloride.
Inspect all finished exhaust vent/air intake piping to ensure:
Vent pipe and fittings are of approved material.

Acceptable size, length and number of elbows on

combined vent pipe 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 supplier's
instructions.
The exhaust vent system and terminations may be
installed in the vertical exhaust vent type of termination.
CAUTION
Exposure to corrosive materials can cause heat
exchanger corrosion and failure.
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.
CAUTION
If the boiler has been exposed to high dust levels, all burners
and the heat exchanger must be cleaned prior to use.
Note: 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.
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