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Combustion Air Requirements - Bosch 330-PN-N Installation Manual

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12 | Installation instructions
Fig. 7
Support board
[1] Wall studs
[2] Support board
[3] 1"x4" Space board
Fig. 8
Secure heater to wall

Combustion air requirements

The BOSCH PRO 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
6 720 644 951 (2014/11)
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 building or
structure are not being supplied with a sufficient amount of
make-up air. A wood stove or furnace can pull outside air down
through the BOSCH PRO vent pipe and across the heat
exchanger tubing. If the air is cold enough, the heat exchanger
is at risk of freezing and bursting. Supplying more combustion
air for all combustion appliances is the solution. Follow the
instruction on venting and checking the adequacy of make up
air. A HVAC specialist should be consulted on how to provide
more combustion 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 BOSCH PRO 330 PN alone.
b) Installations in structures that have been tightly constructed
(air infiltration rate of 0.40 ACH or less) must be provided for
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
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.
330 PN



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