The Bosch PowerStar AE115 and AE125 Electric Tankless Water Heaters provide whole house instant domestic hot water using electricity to heat the water. Both of the PowerStar electric tankless water heaters require 240/208-volt electric power for installation and operation. The PowerStar AE115 requires a minimum 150-amp service, and in the US will require the installation of 2-double pole 40-amp circuit breakers, in Canada the installation of 1-double pole 80-amp circuit breaker is required. The AE125 requires a minimum 200-amp service, and will require the installation of 3-double pole 40 amp circuit breakers, in Canada the installation of 1-double pole 120-amp circuit breaker is required. The Bosch PowerStar units will supply an endless supply of hot water at temperatures up to a maximum temperature of 131-degrees F/ 55-degrees C. However, with tankless the endless supply comes at a price because the water is heated instantly as it passes through the unit so the flow through the unit must be slow enough to allow the water to reach the desired temperature. The temperature of ground water varies in different latitudes with average temperatures in degrees F the high 60’s and 70’s for the southern states, high 50’s and low 60’s for the middle states, and high 30’s to low 50’s in the cooler northern states. According to Bosch the AE115 is only considered to be a whole house tankless water heater when the ground water temperatures are above 60-degrees F/ 15.6-degrees C when ground water temps are lower it may be used as a point of use water heater. Consult the table below to see the amount of water the units can deliver at various rates of temperature rise taking into consideration the temperatures the incoming water supply will be coming to your home in the winter months.
| Temperature Rise /Model | AE115 | AE125 |
| 45F/7.72C Temperature Rise | 2.6-gpm/9.84- L/min | 4.0-gpm/15.1- L/min |
| 50F/10C Temperature Rise | 2.3-gpm/8.71- L/min | 3.7-gpm/14- L/min |
| 60F/15.6C Temperature Rise | 2.0-gpm/7.57- L/min | 3.0-gpm/11.4- L/min |
| 70F/21.1C Temperature Rise | 1.7-gpm/6.44- L/min | 2.6-gpm/9.84- L/min |
| 80F/26.7C Temperature Rise | 1.5-gpm/5.68- L/min | 2.2-gpm/8.33- L/min |
Some of the common water flows in your home would be a shower, which flows a maximum of 2.5-gpm/9.46- L/min per showerhead, a kitchen faucet, which flows 2.2-gpm/8.3 L/min, and lavatory faucets, which flows 1.5-gpm/5.7-L/min.
A flow switch, which detects water flowing through the unit, controls the heating of water in a tankless water heater and turns on the heater modules maintaining the temperature, which is set by the knob between 95-degrees F/35-degrees C up to a maximum of 131-degrees F/ 55-degrees C. The Bosch PowerStar AE115 requires a 0.6-gpm/2.27- L/min minimum flow to turn on and the Bosch PowerStar AE125 requires a 0.8-gpm/3.03- L/min minimum flow to turn on. The water then flows through the 40-amp heater modules where it is heated to the set temperature. The Bosch PowerStar AE115 has two heater modules and the Bosch PowerStar AE125 has three heater modules. For safety each heater module has a safety cut out switch, which will kill power to the module if the temperature goes too high. Both the AE115 and the AE125 are the same size 15½” X 15¼” X 4½” with the AE115 weighing 20 lbs/9.07 kilos and the AE125 weighing 22 lbs/9.98 kilos. The Bosch PowerStar AE115 and AE125 Electric Tankless Water Heaters are supplied with a Ten-Year Warranty.