The 125FX model from Bosch is a model from the Aquastar line of products. It is similar to the 125HX model. They have the same heater. The difference between these two models is that the 125FX has a vent built in. The 125 FX needs a plug for the vent and electricity for the ignition. It has an energy rate of 0.80 which is excellent, because a usual tank based water heater has an energy factor of only 0.59. The fuel for this model can be gas or propane.
It is very important to know that the venting for this model can only be done horizontally. That means it must be vented trough an outside wall. The average efficiency that this model got in the tests is 82%. The lowest flow rate is 0.5 gallons per minute and it can rise the temperature of the water depending on the flow rate this way: It can achieve a temperature rise of 90°F at a flow rate of 2.3 gallons per minute. The temperature rise is 75°F at a flow rate of 2.7 gallons per minute. At 3.1 gallons per minute, the highest temperature rise can be 65°F. The temperature rise that can be achieved at 3.6 gallons per minute is 55°F. The other Aquastar models designed for only one major appliance can achieve this temperature rise only at a flow rate of 3.3 gallons per minute. At 4 gallons per minute, the temperature rise is as high as 45°F.
Now I’m going to tell you about the details you will need to install this model. The water connection type is 1/2 NPT. For the gas the connection type is also 1/2 NPT. The water pressure should be between 18 PSI and 150 PSI. The lowest propane pressure should be 11 W.C. and 7 W.C. if it’s a natural gas. The warranty for this model is as for the other Aquastar models. You have a 12 year warranty on the heat exchanger if you use the gas tankless water heater for a single family home. If not, you only get 2 years for the heat exchanger. For all the other parts you get a 2 year warranty.
The Bosch125FX Aquastar gas tankless water heater was designed to be used for a single major appliance, and if that is what you are looking for this is the product for you. The price for this model is somewhere around $700.