If you have a solar water heating system or a wood water heating system and you need a tankless water heater, which is good as a backup heater, then the perfect model for you is the Bosch Aquastar 125BS gas tankless water heater. If the water that was preheated is at the temperature that you want it to be, the 125BS burners turn off. You can buy this model for gas or propane.
The 125BS is a very efficient model, the efficiency is 82%, while the energy factor is 0.69 for gas and 0.79 for propane. The lowest flow rate for this model is 0.5 gallons per minute. The temperature rise of the water is achieved by this model this way:
The highest temperature rise the water can reach is 90°F, which is at a flow rate of 2 gallons per minute. The second best temperature rise achieved is 75°F at a flow rate of 2.4 gallons per minute. The temperature rise of 65°F can be reached at a flow rate of 2.8 gallons per minute. 55°F is the temperature rise this model can achieve at a flow rate of 3.3 gallons per minute. The lowest temperature rise that the 125BS can achieve is 45° at a flow rate of 4 gallons per minute.
It won’t be so easy to install this model, it is as hard to install as almost all the other gas models. That’s the price you have to pay for efficiency. For the installation, the following details will be useful: The water and gas connection type is 1/2 NPT. The size of this model is also important to the installation process: its height is 29 3/4, the width is 18 1/4 and the depth is 8 3/4. The 125BS is one of the few models that weigh only 44 lbs. The water pressure should be between 18 PSI and 150 PSI. The propane pressure shouldn’t be lower than 11 W.C. and the gas pressure shouldn’t be lower than 7 W.C.
The warranty is pretty impressive, if you use the product for what it was designed. You get a 12 year warranty for the heat exchanger if you use it for a single family dwelling. If you use it in other circumstances then you get only 2 years for it. For all the other parts, you get a 2 year warranty. The Bosch Aquastar 125BS is perfect as a backup heater.