Refer to the water hardness map in determining the water hardness level. This is only a general indicator, for example - well water will be much higher than city water as shown on this chart. For reference: gpg = grains per gallon; ppm = parts per million (also expressed as mg/L).
The size of the incoming water supply line going to your house is critical in determining the proper unit. The SB-150 will handle up to 1 1/4" pipe, and the SB-175 will handle up to 1 1/2" pipe. If you have 1 1/4" pipe and hard water of over 14 gpg, it may be best to upgrade to the SB-175.
The SB-150 and SB-175 will work on copper, cpvc, pvc or pex pipe. If the house has galvanized, or magnetic pipe (when a magnet will stick on the outside of the pipe), a small section of pipe should be cut out where the signal cable goes and replace it with pvc or copper pipe.
If your home is large (over 5,000 square feet) or has multiple levels or several bathrooms, the SB-175 should be installed.
