Bosch 520-HN -L Manual page 15

Fig. 10 Vent Adaptor for High Altitude Installations
Freeze prevention
In cold climates, components of a tankless water heater can
freeze and burst from negative draft. A leading cause of
negative draft is combustion appliances in the building not
being supplied with sufficient combustion air. A wood stove or
furnace can pull its combustion air from the water heater's vent
pipe, allowing the cold incoming air to freeze the cold water in
the heat exchanger. Supplying more combustion air for all
combustion appliances is the solution. A HVAC specialist
should be consulted to design solutions for providing more
combustion air.
In cold climates where backdraft is a problem, the freeze
prevention kit accessory (7709003775) should be installed.
Masonry chimney
Masonry chimneys shall be built and installed in accordance
with NFPS 211 or local codes. A minimum 5" diameter gas vent
pipe (metal double wall Type B), or an approved clay flue liner
or a listed chimney lining system must be used when venting
into a naturally drafting, internal masonry chimney. 6 inch is
required in elevations greater than 2000 feet, see Fig. 6. Local
codes may require the use of both gas vent and an approved
lining system when venting into a masonry chimney. The
Commonwealth of Massachusetts requires the use of a listed
liner. Lining systems include approved clay flue lining, a listed
chimney lining system or other approved material that will
resist corrosion, erosion, softening, or cracking from exhaust
flue gases at temperatures up to 1800 degrees F. The lining
system must be listed for use with naturally drafting, draft hood
equipped gas appliances. Follow local codes and refer to NFGC
54 and NFPA 58.
Existing interior masonry chimney
The metal gas vent pipe should be permanently mounted inside
the masonry chimney. Double wall Type B gas vent is
520 HN
5" X 6" ADAPTOR
USED AT HIGH
ALTITUDE
recommended. The masonry chimney may have to be tile or
metal lined before the insertion of the gas vent pipe; check local
codes for clarification. The lining material must be listed for use
only with naturally drafting, draft hood equipped gas
appliances. Follow manufacturer's instructions for installation
of listed lining material. You may not vent any other fuel burning
appliances into any free space remaining in the chimney. The
minimum vertical gas vent length within the masonry chimney
must be no less than 5 ft (1.5 m); the vent terminator must
extend at least 3 feet (0.9 m) above where the chimney meets
the roofline and at least 2 feet (0.6 m) higher than any vertical
wall or similar obstruction within 10 feet (3.1 m). The top of the
gas vent must have an approved vent terminator. See Fig. 12.
ESTABLISH A ONE
FOOT RISE
BEFORE
ANY ELBOWS
Fig. 11 Pitch roof
[1] Listed vent cap
[2] Lowest discharge opening
[3] Listed gas vent
[H] H (minimum) height from roof to lowest discharge
opening
[X] Roof pitch is X/12
[A] Minimum 6 feet (1,8m)
Installation instructions | 15
6 720 644 942 (2014/11)