A weekend or seasonal home does not fit the usual sizing shortcut, which assumes the same people use the same water every day. Here the water use arrives in bursts. A unit that looks right on a monthly average can fall short on the one weekend when the house is full. Sizing for this kind of home means counting the peak, not the typical day.
Count the full weekend
Write down how many people stay on a full weekend, including guests, children, and visitors who stay overnight. Then count the water use for that weekend: showers, laundry loads, dishwasher runs, and any outdoor or extra fixtures that get used when the house is busy. This list is the number your installer should size against. Ask them to show the sizing with your figures, not just a chart from a brochure.
Separate the peak from the usual
Compare the full-weekend count with a normal quiet week. If the two are far apart, the unit has to handle the peak without running short, and it also has to behave sensibly during the quiet stretches. Ask the installer how the unit will perform when it has been idle for long periods between busy weekends, and what the plan is if a larger group arrives on short notice.
Ask about the fixtures that stay on
Some homes have appliances or systems that draw water even when no one is staying there, such as an ice maker, an irrigation timer, or a utility-room fixture. Make a list of anything that runs on its own. Ask the installer whether those draws are counted in the sizing or left out. A sizing that ignores them will look smaller on paper than the real use.
Confirm the water source and supply
A seasonal property may be on a different supply than your main home, or it may have a different pressure at the street connection. Ask the installer what water supply the property uses and whether that supply was checked during the site visit. Do not rely on a sizing chart built for a full-time household on a different line.
Check what the quote assumes
Before you sign, confirm the occupancy figure written on the quote. If it matches a typical household and not your weekend count, ask for a revised sizing in writing. A quote built on the wrong number is the most common reason a seasonal home ends up with a unit that works in June and runs short on a holiday weekend.