Tankless Water Heater Comparison: Compare Gas Tankless Water Heaters

Gas Tankless Water Heater Review and Comparison

Gas Models (LP & Natural Gas)

Provides Hot Water For (1)

Venting

BTU Input

Flue Size

Built-in Power Vent

Gas & Water Connections

GPM @ 110F (55 deg. temp rise) (2)

Limited Warranty(3)

Notes

Bosch 38B

2 minor applications

Vertical (thru roof)

40,000

4 inch

No

½” NPT

1

12 years

Standing pilot.  Requires a 4" double wall vent pipe and can be vented through an existing vent.  Ideal for a camp or cottage.

Bosch 125B

1 major application

Vertical (thru roof)

117,000

5 inch

No

½” NPT

3.3

12 years

Standing pilot.  Designed to vent vertically, but can vent horizontally with AQ1 power vent. Requires a 5" type-b double wall vent.  If the AQ1 is used, requires a 4" single wall vent pipe after the AQ1.

Bosch 125HX

1 major application

Vertical (thru roof)

117,000

5 inch

No

½” NPT

3.3

12 years

Hydro-Ignition (3).  Requires no pilot, batteries or electricity.  Designed to vent vertically, but can vent horizontally with AQ1 power vent.   Requires a 5" type-b double wall vent. If the AQ1 is used, requires a 4" single wall vent pipe after the AQ1.

Bosch 125FX

1 major application

Horizontal (thru wall)

125,000

4 inch

Yes

½” NPT

3.3

12 years

Electronic ignition(120VAC).  Built-in power vent allows horizontal venting up to 15 ft with 2 elbows. Requires a dedicated 4" stainless steel single wall vent pipe.

250SX

2 major applications

Vertical or Horizontal

175,000

3 inch

Yes

¾” NPT

5.2

12 years

Electronic ignition(120VAC).  Requires a dedicated 3" stainless steel single wall vent pipe.  Has a built-in thermostat and is room sealed – can be installed in a closet.

  1. Note: A minor application would be a sink and a major application would be a shower, washing machine, etc.
  2. Note: Flow rates are based on an inlet water temperature of 55 degrees.
  3. Note: Term of limited warranty(on heat exchanger) listed is based on professional installation by a licensed plumber or contractor. If installed individually the Bosch gas tankless water heaters will have a 10 yr warranty with 2 years on parts.
  4. Note: The AquaStar 125HX uses a hydro-generated ignition. BOSCH engineers installed a small turbine wheel inside the unit attached to an electromagnetic wire.

Gas Models (Natural Gas and LP Propane) General Installation Requirements:
**See instruction manual for requirements in detail**

Venting:
125B, 125HX Models: 5" type B (double wall) vent - 6' minimum vertical height (no elbows), AQ1 Powervent option will allow a vent run of 100 feet subtract 5 feet for every elbow.
125FX Model : 4" dedicated, sealed, single wall vent (stainless steel or 26+ gauge galvanized). 15' maximum run with two elbows - must terminate horizontally.  FXHOOD required.
240FX Model: 4" dedicated, sealed, single wall vent (stainless steel). 21' maximum run - subtract 5' for each elbow. FXHOOD recommended for horizontal termination. 

250SX Model: 3" dedicated, sealed, single wall vent (stainless steel).  26' maximum run with one elbow - subtract 2.5' for each elbow.

Combustion Air:

  • 125B, 125HX, 125FX:  Minimum 5,900 cu. ft OR permanent inlet air supply for the heater.
  • 240FX: Minimum 8,250 cu. ft OR permanent inlet air supply for the heater.
  • 250SX:  0 cu. Ft if utilizing the inlet pipe system otherwise 8,250 cu. ft.

Note: 38/125/240 models cannot be installed in a mobile home, bedroom, bathroom, or any other confined living space normally kept closed.

 Gas Line:  Gas line must be properly sized to meet required BTU input. 

Natural Gas: Maximum Length of Pipe Run

Nominal Iron Pipe Size

Nominal Iron Pipe Size

½ “

¾”

1 “

125B, 125HX, 125FX

10 ft

40 ft

150 ft

 

LP (Propane): Maximum Length of Pipe Run

Nominal Iron Pipe Size (copper)

Nominal Iron Pipe Size

5/8 “

¾”

125B, 125HX, 125FX

20 ft

60 ft

250SX

10 ft

30 ft