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Bosch 635
Bosch Electric

BOSCH AquaStar Tankless Propane and Natural Gas Water Heaters 


The BOSCH AquaStar tankless water heaters are redefining how homeowners throughout North America heat their water.

Tankless hot water heaters provide endless hot water, save energy and save space.  

Sized for most homes and small businesses the BOSCH 125 Series water heaters supply one major hot water outlet at a time [e.g. One shower running at a time]. Delivers up to 3.5 gallons per minute.

The revolutionary hydro-generated ignition system incorporates hydro technology into a domestic water heating appliance.

How tankless water heaters work:
1. When you open a hot water tap, cold water enters the heater and triggers the heating elements or burners.  Your hot water tap acts as an ignition key for the energy used to heat the hot water you need.

2. The water is heated as it flows through the heating elements or heat exchanger. As the water flow varies, the unit adjusts the heating elements or burner flame to maintain a constant temperature and maximum energy efficiency.

3. When the hot water tap is turned off, the heating system also turns off.

What you save when using a tankless heater:
Your water heater is the second biggest consumer of energy in your home [after home heating]. Therefore it is where you can significantly reduce the costs of your annual energy consumption. Why keep a storage tank full of hot water 24 hours a day when the average household use is less than an hour everyday?

When water is heated in a tank, the inside walls will soon begin to build up mineral deposits. The scale build up on the bottom of the tank can cause it to decrease in efficiency by as much as 50% over 10 years and the subsequent corrosion of the tank's inside wall will eventually cause it to leak.
 

Bosch The ProTankless™ Gas Water Heaters Specifications

 

GWH 635 ES / ESO

GWH 425 HN

GWH 425 EF

Technical Specifications

Rated input (BTU/HR)

175,000

117,000

130,000 NG / 125,000 LP

Efficiency

Thermal

87%

80% NG / 83% LP

80% NG / 82% LP

Energy Factor

.85

.85 NG / .84 LP

.78 NG / .81 LP

Min. flow rate (GPM)

.8

.5

.5

Power Input (Btu)

NG

35,000 - 175,000

28,000 - 117,000

28,000 - 130,000

LP

31,000 - 175,000

28,000 - 117,000

28,000 - 125,000

Ignition

Electronic

Hydro-Generated*

Electronic

Modulating Gas Valve

NA

NA

Yes

Voltage

120 VAC

N/A

120 VAC

Vent Size

3"/ NA

5"

4"

Vent Options

Direct Vent Room-Sealed Combustion / NA

Conventional Flue

Power Vented Through Sidewall

Capacity

6.4 GPM @ 45°F rise

4.25 GPM @ 45°F rise

4.25 GPM @ 45°F rise

Dimensions (inches)

Height

23½" / 23½"

29¾"

29¾"

Width

15¾” / 15¾”

18¼"

18¼"

Depth

8½” / 8½”

8¾”

8¾”

Weight (lbs)

47

40

44

Flow Rates (GPM)

 

90° F rise

3.2

2.1

2.3

75° F rise

3.9

2.4

2.7

65° F rise

4.5

2.9

3.3

55° F rise

5.2

3.4

3.8

45° F rise

6.4

4.2

4.6

Life Expectancy

20+ years

20+ years

20+ years

Installation Specifications

Gas Connection

¾" Male NPT

½" Male NPT

½" Male NPT

Water Connection

¾" Male NPT

½" Male NPT

½" Male NPT

NG Gas Pressure

Min

NA

7" WC

7" WC

Max

NA

14" WC

14" WC

LP Gas Pressure

Min

11" WC

11" WC

11" WC

Max

14" WC

14" WC

14" WC

Water Pressure (psi)

Min

30

30

18

Max

150

150

150

Electrical Supply

20 VAC 50/60 Hz
Idle 40mA, Operation, 2.5A

None

120 volts/1.2 amps (plugs in)

Vent Size

NA

5" (double-wall type B)

4" (single-wall stainless or galvanized)

Optional Accessories

Wireless Remote Control

Power Vent Kit - AQ1

Horizontal Vent Terminator - FXHOOD (FXHOOD required)

Previous model information:

Specs
by Model

38B

125B

125BO

125BS

125BL

125HX

125FXw FXHood*

 Efficiency

NG: 80%; LP: 80%

NG: 80%; LP: 86%

NG: 80%; LP: 86%

NG: 80%; LP: 86%

NG: 80%; LP: 86%

NG: 80%; LP: 83%

NG: 80%; LP: 82%

@ 55ºF Rise

1.0

3.3

 

3.3

3.3

3.3

3.3

@ 65ºF Rise

0.9

2.8

 

2.8

2.8

2.8

2.8

@ 75ºF Rise

0.8

2.4

 

2.4

2.4

2.4

2.4

@ 90ºF Rise

0.6

2.0

 

2.0

2.0

2.0

2.0

BTU Input

40,000

117,000

 

117,000

117,000

117,000

125,000

Energy Factor

.66

.69

 

.69

.69

.78

.78

GPM@ 45ºF

1.3

4.0

 

4.0

4.0

4.0

4.0

Net Weight

18 lbs.

39 lbs.

 

42 lbs.

44 lbs.

40 lbs.

44 lbs.

Optional Accessories

None

Power Vent

 

Power Vent

Power Vent

Power Vent

 

Product Features:

  • All water parts are high quality copper and plastic
  • Unit is constructed with stainless steel and aluminum
  • Casing is finished with baked epoxy
  • Heat exchanger is made of solid copper
  • Burners are made of stainless steel
  • Unit has a safety thermocouple and overheat shutoff protection
  • CSA design certified, Compliant with ASHRAE 90.1

Model

Input (Btu)

Efficiency

GPM Flow Rate @ 55°F rise

Vent Type

Vent Size

Ignition System

Activation Flow in GPM

Heat Exchanger Warranty

38B

40,000

80%

1.2

Natural

4"

Pilot

0.6

12 Years

125B

117,000

82%

3.3

5"

0.5

125BS

125HX

Hydro

125FX

130,000

80%

3.6

Forced

4"

Electronic

250SX
250SXO

175,000

87%

5.2

Direct

3"

Electronic

0.8

 

Manufacturer's Warranty:

  • 12 years on the heat exchanger when professionally installed
  • Proper product selection supported by customer service agent
  • Proper operation supported by solar engineer tech assistance
  • Toll-Free help line and/or online e-mail tech support

Product Benefits:

  • Endless hot water for the home or office
  • Can reduce energy costs up to 50% 
  • Never stores hot water [preventing rust and leaks]
  • High energy factors [cuts greenhouse gas emissions up to 50% compared to storage tank]
  • Steady temperature at varying flow rates
  • Small, light and easy to install
  • Hangs on wall - saving floor space
  • Stores only cold water, reducing the risk of bacteria growth
  • Designed and built to last 20+ years
  • 82% efficient for life of the heater
  • Natural gas/propane energy factor of .69-.84 [tanks .52-.62]
  • Electric energy factor of .99 [tanks .80-.90] 

Link to Bosch web site

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Last modified: April 10, 2017