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Applications manual
Application manual | 11.2007
Bosch Water Heating
2.8 Bosch GWH 425 HN
Features:
Hydro-generated ignition
80% thermal effi ciency
Endless hot water for one major application at a time
Venting: 5" double wall B-vent — natural draft
Modulating gas valve — constant temperature at varying flow rates
Model GWH 425 HN N for natural gas (NG) supply
Model GWH 425 HN L for liquid propane (LP) supply
15-year warranty
Qualifi es for $300 tax credit
GWH 425 HN Technical Specifi cations
Gas input Natural Gas: 30,735 - 117,000 BTU
LP Gas: 30,735 - 117,000 BTU
Minimum fl ow to activate 0.6 gallons per minute (gpm)
Flow rates 45˚F rise @ 4.2 gpm
55˚F rise @ 3.4 gpm
65˚F rise @ 2.9 gpm
77˚F rise @ 2.4 gpm
90˚F rise @ 2.1 gpm
Thermal Effi ciency NG: 80% LP: 80%
Dimensions 25.75" h x 16.75" w x 8.5" d
Weight 33 lbs.
Modulating gas valve yes
Ignition Hydro-generated
Accessories Horizontal vent kit (AQ4) - power
vent kit for horizontal venting
GWH 425 HN Installation Specifi cations
Gas connection ¾" Male NPT
Water connections ¾" Male NPT
NG gas pressure Minimum: 7" W.C.
Maximum: 14" W.C.
LP gas pressure Minimum: 11" W.C.
Maximum: 14" W.C.
Water pressure
(Static)
Minimum: 30 PSI
Minimum well pressure: 40 PSI
Maximum: 150 PSI
Electrical supply 120VAC - plugs in
Vertical venting 5" minimum diameter - natural
draft
Horizontal venting AQ4 horizontal vent kit required
for horizontal terminations
GWH 425 HN Installation Clearances
Top (A) 12"
Front (B) 4"
Back 0"
Sides 4"
Floor (C) 12"
LISTED VENT CAP
MINIMUM 6
FEET (1.8M)
LISTED GAS VENT
ESTABLISH A ONE
FOOT RISE BEFORE
ANY ELBOWS
Fig. 2 Venting confi guration
Installation guidelines:
Venting:
5" minimum diameter — do not reduce vent size
Refer to installation manual for vent material options
Do not combination vent with any power vented appliances
Establish a one-foot rise before any elbows
Minimum vent height - 6 feet
Horizontal sections must slope upwards at least ¼" for every foot
of the horizontal length and be properly supported
Gas piping:
Heater will not function properly without adequate supply gas
pressure
Any appliance connector should be ¾" minimum diameter
Plumbing:
Install the included pressure relief valve and pipe to suitable drain
Minimum piping diameter is ¾"
Do not solder directly to connections on the bottom of the unit
Use full port ball valves for isolation valves