Combustion Air Requirements; Venting - Bosch 520-HN -L Manual

Fig. 8 Secure heater to wall
4.4

Combustion air requirements

The Protankless water heater holds cold water in its copper
heat exchanger and water valve when not in use. Because of
this, any cold air that comes down through the unit's vent pipe
is capable of freezing these components. This Installation
Manual specifies the minimum vertical vent pipe and the
amount of combustion air required for this unit. When all
requirements are followed, the unit will operate properly and
safely. However, there may still be a risk of freezing due to
negative draft if all the combustion appliances in the structure
are not being supplied with sufficient combustion air. A wood
stove or furnace can pull it's combustion air from the
Protankless vent pipe. This allows the cold infiltrating air to
potentially freeze the cold water in the water heater. Damage
from freezing is not covered under the manufacturer's
warranty. Supplying more combustion air for all combustion
appliances is the solution. Follow the instructions on venting
and checking adequacy of combustion air. A HVAC specialist
should be consulted to design solutions for providing more
make-up air if necessary. Observe the following instructions
concerning combustion air.
Appliances located in unconfined spaces:
a) An unconfined space is one whose volume is greater than 50
cubic feet per 1000 Btu per hour of the combined rating of all
appliances installed in the space. That would be 5850 cubic
feet for the Protankless 520 HN alone.
b) Installations in structures that have been tightly constructed
(air infiltration rate of 0.40 ACH or less) must be provided with
520 HN
combustion air per the National Fuel Gas Code. Consult a HVAC
specialist if your air infiltration rate is questionable.
Appliances located in confined spaces:
The confined space must be provided with two permanent
openings, one commencing within 12 inches of the top and one
commencing within 12 inches of the bottom of the enclosure.
Each opening must have a minimum free area of one square
inch per:
• 1000 Btu/hr if all air is taken from inside the building.
• 2000 Btu/hr if all air is taken from the outside by horizontal
ducts.
• 4000 Btu/hr if all air is taken from the outside by direct
openings or vertical ducts
Or the confined space must be provided with one permanent
opening or duct that is within 12 inches of the ceiling of the
enclosure. This opening must have a minimum free area of one
square inch per:
• 3000 Btu/hr if all air is taken from the outside by a direct
opening or vertical duct
Louvers, grills and screens have a blocking effect. If the
effective free area is not known, increase the sizes of your
openings by 400% if your louvers are wood and by 135% if your
louvers are metal. Refer to the National Fuel Gas Code for
complete information. In buildings of tight construction all air
should be taken from outside.
4.5

Venting

DANGER:
▶ Do not reduce the vent pipe size. Do not
put an elbow directly on top of heater.
Failure to follow venting requirements
may cause dangerous exhaust gases to
enter living space.
▶ Minimum vent pipe diameter: 5inches
▶ Minimum vertical vent height: 6 feet, with no elbows
▶ Establish 12 inch rise before any elbow
The heater must be vented to the outside following all local
ordinances and specifications for installing a gas appliance
vent or chimney. The heater must be located as close as
practicable to a vertically rising chimney or vent that has a
listed vent cap at its termination point. The venting system
must be designed and constructed so as to develop a positive
flow adequate to remove flue gasses to the outdoors. Consult
the National Fuel Gas Code if the vent will have elbows or share
venting with another natural draft appliance.
Installation instructions | 13
6 720 644 942 (2014/11)