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Combustion Air Requirements - Bosch 520-HN-N User Instructions

Flow modulated with hydro-generated ignition suitable for heating potable water only - not approved for space heating purposes (intended for variable flow applications with steady cold water inlet temperatures)
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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 AquaStar 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
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 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
6 720 644 942
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.
Mounting Heater
The 520 HN is approved for installation on a combusti-
ble wall provided the floor covering below the heater is
noncombustible. For installations in an alcove or closet,
maintain the minimum clearances to combustible and
non-combustible materials listed in Fig. 4.
Warning: before starting installation:
B check that there are no loose parts
inside the appliance
B ensure that gas pipe, gas valve, and
burner have no damage and are
properly fitted.
B Read chapter 2.2 to verify proper gas
type and to verify all parts are included
in box.
Front cover must be removed in order to
instructions below).
Remove cover and inspect.
B Remove the flow control and power adjustment
B Unsrew the cover fixing screws, see Fig. 10.
B Loosen the two Phillips head screws located on
bottom rear of cover. Remove cover by pulling it
outward and then lifting upwards.
B Ensure that the flue terminal is clear.
B After inspection, replace front cover and tighten
Install incandescent particle tray.
B Install incandenscent particle tray using screws
provided as shown in Fig. 9.
Incandescent particle tray
Fig. 9
Incandescent particle tray illustration
Installation instructions



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