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Combustion Air Requirements; Mounting The Heater - Bosch 38B LP Installation And Operating Instructions Manual

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This product is not approved for manufactured homes
(mobile home), recreational vehicles (RV) or boats.
Reference ANSI Z21.10.3.
This product is neither designed or approved for
outside installations.
The AquaStar water heater holds cold water in its copper
heat exchanger and brass water valve when not in use.
Because of this, any cold air that comes in 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. The vent pipe must not be restricted and its 6 foot
minimum height (provided there are no elbows) must
terminate 2 feet above any obstruction within a 10 foot
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 area are not being supplied with a sufficient amount
of make-up air. A wood stove or furnace can rob the make-
up air in the AquaStar's vent pipe, leaving the cold infiltrating
air capable of freezing the cold water in the AquaStar heat
exchanger. More make up air is the solution. Follow the
instructions on venting and checking adequacy of make up
air. A HVAC specialist should be used to design solutions
for providing more make-up air if necessary.
Observe the following instructions concerning combustion
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 75% if your louvers are wood and by 30% 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. That would be 2000
cubic feet for the Aquastar 38B alone.
The Aquastar 38 B is design certified for installation on a
combustible wall and for installation in an alcove or closet
with the minimum clearances to combustible and non -
combustible construction listed below
A. Top 12 inches ( 305 mm)
B. Front 4 inches (102mm)
C. Back 0 inches
D. Sides 4 inch (102mm)
E. Bottom 12 inches (306 mm)
Clearance from vent is dependent upon the clearance rating
of the venting material used. For example: type B-1 vent is
approved for 1 inch clearance.
Note: Minimum clearance to combustible materials should
not be less than 6" for single wall flue pipe. Note that this
clearance can be reduced if combustible material are
protected as per table VI of the National fuel Gas Code or if
Type B gas vent is used.
The Aquastar 38 B is design certified for mounting on a
Secure the two L shaped hooks, which are provided with
heater, to a wall surface. Place them 5 ½" apart as
shown in Fig. 1.
Do not install this appliance on a carpeted wall or over floor
covering which is combustible, such as carpet. The heater
must be mounted on a wall using appropriate anchoring
materials. If wall is a stud wall sheathed with plasterboard,
it is recommended that support board(s), either 1x4's
or 1/2" (minimum) plywood first be attached across a
pair of studs and then the heater should be attached
to the support boards. See Fig 1.
Expansion and contraction of piping due to changing water
temperature in the pipes imparts movement to the heater
which, if mounted directly to a brittle, friable board, such
as plasterboard, can cause failure of mounting.
In earthquake-prone zones, CEC recommends that
installers use a large washer and lag screw through the
existing holes used to hang the heater to affix the upper
third of the heater to the mounting board. To affix the
lower third of the heater, CEC recommends that two new
holes be drilled in the heater's frame, each one 16 inches
below the top two holes, and that washers and lag
screws be used to secure the lower portion of the heater
to a spacing board.
Before installing the unit, be certain you have the correct
heater for your type of Gas – Propane or Natural Gas



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