Bosch Appliances Model GWH 425 Combustion air requirements, Appliances located in confined spaces

Installation instructions

3.5Combustion 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 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 GWH 425 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 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.

8 6 720 608 034