A bigger water softener is not a free upgrade. A unit with more grain capacity costs more to buy, usually needs a larger brine tank, may take more floor space, and can waste salt and water when it is bigger than the household needs. Oversizing shows up on the quote once and on the salt and water bills every month after that.
Start with the number the quote is built on
Every sizing decision begins with two figures: how hard the water is and how much of that hardness the household uses each day. Hardness is usually written in grains per gallon. Ask the installer which hardness figure they used and where it came from. Was it a test of your water, or a general figure for the area? A general figure can be far enough off to change which unit you need, so get the source in writing before you compare prices.
What pushes the price up
Grain capacity is the main lever. Higher capacity generally means more resin, a larger tank, and a bigger brine tank. Those parts raise the equipment price, and often the installation price too, because larger units are heavier and may need more room, a larger drain connection, or a different placement. Ask each vendor to state the rated grain capacity in writing so you are comparing the same thing.
Ask whether each price includes the valve, bypass, drain fittings, and brine tank. Two quotes for the same stated capacity can look far apart simply because one includes those parts and the other leaves them out.
What an oversized unit costs you later
A unit larger than needed holds more water between regenerations, so it may regenerate less often than a right-sized unit would. That sounds efficient, but the real cost depends on the control settings. If the unit regenerates on a fixed schedule instead of based on water use, it may run on days when little water was used. Ask how the control will decide when to regenerate and what setting the installer will program for your hardness and household size.
Salt use also depends on how capacity and the salt dose setting work together. A large unit paired with a generous salt setting can use more salt than the household needs. Ask what salt dose the installer plans to program and whether that dose matches the rated capacity of the quoted unit.
Price the three costs side by side
Compare the purchase price, the installation price, and the running cost as three separate lines. For each quote, write down the grain capacity, the salt dose setting, the expected regeneration frequency for your household, and the water used in each regeneration. Ask the vendor to explain their estimate in those terms. A quote that gives a purchase price without showing expected regeneration frequency leaves out the number that drives the monthly bill.
Questions to ask before you sign
Ask which hardness figure the installer used and where it came from. Ask what grain capacity the quoted unit is rated for, and whether a smaller or larger unit would fit your hardness and household better. Ask how often the unit is expected to regenerate, what salt dose it will be set to, and whether the price includes the bypass, drain fittings, and brine tank. If the answers are vague, ask for them in writing before you compare totals.
If you want to see how this site weighs price against other criteria, the rating methodology explains the criteria, weights, and scale behind the scores.