A full-time household uses water on a steady rhythm, so a softener is usually sized to an average day. A second home or seasonal house has a different pattern: long stretches with almost no use, then a weekend with six people showering and running the dishwasher. Sizing for that pattern asks different questions.
Start with the occupancy record
Write down how the house was actually used over the past year: the weeks it was empty, the weeks it had guests, and the largest group that stayed at one time. Count people per stay, not just the number of bedrooms. The peak week is the one that matters most for sizing, because a softener that is too small for a full house will run out of soft water at the worst moment, while an average-week figure looks fine on paper.
Ask whether the control regenerates on use or on a clock
Ask the company which regeneration mode the control uses. A demand-based control regenerates after a set volume of water is used, so an empty house does not trigger a cycle. A time-based control regenerates on a schedule whether or not anyone is home, which can waste salt and water in a house that sits empty for weeks. Some controls also offer a vacation or days-off setting. Ask whether yours has one, who will set it, and get the answer in writing.
Ask what happens during a long vacancy
Ask what the system does when it sits unused for a month or more. Ask whether the brine tank should be checked before a long stay, whether the company recommends a specific setting for vacancy, and what you should do when you return. Find out whether the unit needs a short run before the first tap is fully soft after a long idle period. Write the answers into your house file so the next guest, or your own next visit, does not start from memory.
Size for the peak week and check the water heater
Ask the installer how they arrived at the programmed capacity, and whether they checked it against your peak-week count rather than an average day. Then look at the water heater. A softener can be sized correctly while the hot water supply runs out during a busy weekend, and then the limit is the heater, not the softener. Ask whether the heater's capacity was considered in the plan.
What to get in writing before you sign
Get four things in writing: the regeneration mode, whether a vacation setting exists and how it is set, the peak-week figure used for sizing, and the steps for returning from a long vacancy. A company that has a clear answer to each one has thought about your house, not only the average one on the sales sheet.