Bosch GWH 1000 - Manual (Page 8)

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Installation instructions
3.5 Combustion air requirements
The AquaStar 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 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
Aquastar's 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 AquaStar GWH
1000 P
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 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.