abikerboy, Not Gary S but knowing the hardness may be important for sizing. Do you plan to get married and have kidlets running around? Most homes that I sell and service have a 30 or 40,000 grain unit. If you think it will just be you and a wife with friends now and then a 30,000 should be fine. They both will take the same head. The difference is only how often they will regenerate and if you will run out of soft water B4 it does. Both soften the water the same. The total # of gallons of soft water available B4 regeneration will depend a lot on hardness. What is the well pressure switch set at? That will be telling the GPM. Most softeners need a minimum of 30 PSI constant to work correctly so if your well switch is set at 20-40 it needs to be changed. We have a few homes out here that have in excess of 40 grains hardness per gallon on city water not a well. Thats high. Personally, if you have the room for it, I would just go for the 40,000 grain as the $$$ difference is negligible.