Bosch Therm 940 ES
Tankless Water Heater
Review and Buying Tips

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An overview of the Bosch Therm 940 ES, the largest non-condensing tankless water heater from Bosch, a powerful unit that can meet higher demands for hot water, in homes with up to 4 baths.


The Therm 940 ES is the point-of-use and whole-house tankless water heater that can be used in both residential and commercial applications, working on demand and providing hot water in endless supply. As it is built as the non-condensing unit with only one heat exchanger, the model is capable of providing sufficient water flow in demanding applications, either working as a single unit or combined.

The heater is built as a high efficient device, and as it incorporates a modulating gas valve, it is almost guaranteed to have a high-efficiency operation, optimum performance, and long life.


Flexible installation

The Bosch 940 ES is the the standard type tankless water heater that is designed as the direct vent unit with the gas sealed combustion chamber, and with the help of the dual fan technology, it can be installed and safely used anywhere inside the house. With the right venting kit, it can be installed outdoors too.

The heater can utilize 3” and 4” vents made of stainless steel, which can run either horizontally through the outside wall, or vertically through the roof, reaching maximum length of 61 feet (4” pipe) or 29 feet (3” pipe).

Provide lots of hot water

It’s powerful, and Low NOx gas burner and one long-lasting copper heat exchanger generate lots of power and water flow resulting in increased energy factor of 0.83. Bosch 940 ES is the whole-house water heater where its maximum water flow rate of 9.4 gallons per minute makes it ideal for larger families, using up to four showers simultaneously. Also, the minimum water flow of 3 gallons makes the usage also convenient where a smaller amount of hot water is needed, without using too much energy.

The Bosch 940 ES tankless model can also be paired with the storage tank, and electric mini-tank heater - Tronic, in applications where more hot water is needed, and faster hot water delivery is desired. For larger homes and high-demanding applications, one tankless unit might not be enough, so the recommendation is to use the Intelligent Cascading Kit so up to 24 units can be connected into one system, generating even more hot water.

Variety of applications

Bosch Therm 940 ES

As mentioned before, the Bosch Therm 940 ES model, was built mainly for heating domestic water but can also be used for combined domestic water and space heating.
It is also approved for domestic hot water recirculation applications so you can get hot water faster than if the circulation pump is not used.

The water heater can also be combined with the solar water heater system if the solar panels cannot provide enough hot water, the gas tankless acts as the booster.

Modulation for savings

The advanced features allow gas and water valve modulation, so the power, based on the water needs, automatically adjusts its power from 19,900 to 199,000 BTU, so water is always heated and with just enough power, not more, not less – saving energy and water. Another significant advantage is the real-time diagnostics, represented by the failure codes that show on the LCD, so the problem troubleshooting becomes easier.

As seen from the above technical data and when comparing to other non-condensing models, the Bosch Therm 940 ES is the most powerful non-condensing tankless water heater that produces the highest water flow of all conventional tankless water heaters from Bosch. Due to the innovative design, the water heater can run on natural or liquid propane gas, while its small and compact design ensures flexible installation and wall mount inside or outside the residential house, commercial office, even the mobile homes.

Safety features

  • Built-in freeze protection inside the heater, down to 5 F but only for the short-term conditions

  • ECO protection against overheating

  • Flame failure device (ionization flame rod sensor)

  • Outlet temperature sensor

  • Backflow temperature sensor

  • Flue temperature sensor

  • Water drop protection

  • Condensate drain


  • Power: 19,900-199,000 BTU

  • Maximum water flow: 9.4 GPM

  • Thermal efficiency: 83%

  • Temperature range: 100-140 F (commercial C 950 ESC models can reach up to 180 F)

  • Accuracy: +/- 2 F

  • Maximum exhaust and combustion air pipe lengths - 63 ft. for twin pipe system or 43 ft. for concentric

  • Vent size: 3 or 4 inch

  • Maximum altitude 8,000 ft.

  • Minimum water flow to activate the unit: 0.5 GPM

  • Water pressure: min 30, max 145 PSI

  • Size: 11” X 18” X 30.5”, Weight: 67 lbs


The Bosch Therm 940 ES can last over 20 years, and most of its components are serviceable. The warranty on the heat exchanger, against leaking, is 15 years.

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