Bosch Appliances GWH-345/450-ESR-N manual Combustion air requirements, Twin pipe, Single pipe

Installation instructions

Fig. 10 Mounting the heater

3.5Combustion air requirements

Warning: In areas where freezing temperatures are common the twin pipe system is recommended. In a single pipe installation, a negative air condition may result in cold air being drawn across the heat exchanger coil causing it to freeze and burst. This failure is not covered under the manufacturer’s warranty.

Warning: When installed in an environment where corrosive chemicals or dirty air are present the twin pipe system is required.

Twin pipe

The GWH-345/450-ESR is designed as a sealed combustion appliance. It is recommended that the combustion air be provided by a dedicated 3” pipe to the outside. If terminating combustion air piping horizontally, pitch vent down 1/4" per foot towards termination to prevent rain from entering the appliance. The combustion air pipe may be constructed of aluminum flex, PVC or any other rigid or semi rigid sealed pipe. The combustion air inlet must be located in such a manner as to provide a minimum 3 foot clearance from the exhaust vent terminator.

The maximum length of the combustion air inlet is 39 feet with one elbow. Subtract 6 feet for each additional elbow. Maximum number of elbows permitted is 4.

Single pipe

Although it is permissible to draw combustion air from inside the structure, it is not the manufacturer’s recom- mended installation method. Always install a 3 inch elbow on the combustion air inlet to prevent foreign objects from falling into the unit (see Fig. 11).

Fig. 11

If a single pipe installation is performed. Use the follow- ing guidelines when providing adequate combustion air for the recirculating water heater as well as any other appliances that may consume air in the space. Always follow local codes if more stringent.

•Appliances located in unconfined spaces:

–a) An unconfined space is one whose volume is greater than 50 cubic feet (1.42 cubic meter) per 1000 Btu per hour (292.81 watts) of the combined rating of all appliances installed in the space. That would be 6200 cubic feet (175.6 cubic meter) of air required for the GWH-345/ 450-ESR alone.

–b) In unconfined spaces in buildings of conventional frame, masonry, or metal construction, infiltration air is normally adequate to provide air for combustion.

–c) Installations in structures that have been tightly constructed (air infiltration rate of 0.40 ACH or less) must provide combustion air per the National Fuel Gas Code. Consult an HVAC specialist if your air infiltration rate is questionable. For these types of installations, the twin pipe system must be used.

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