Describe the added use
List current and expected showers, baths, laundry, and dishes. Ask whether the tenant is likely to share the morning shower period or use hot water at another time. Include fixture flow and any large bath rather than assuming one added person always adds the same demand.
If future use is uncertain, ask the provider to compare a normal scenario and a reasonable heavier-use scenario. State the assumptions so you can revisit them when the occupancy pattern becomes clearer.
Compare storage and recovery
Request the selected model's stored volume, first-hour delivery, and reheating performance in the proposed location. Ask which operating mode supports the estimate and whether backup elements are expected during the busiest period.
A larger tank, a supported mode, or a modest schedule change may offer different costs and convenience. Compare those choices explicitly. Do not promise a tenant unlimited consecutive showers based on the tank's label.
Ask whether electrical supply, space, air, drainage, or related plumbing limits the options. If a bigger model needs additional work, include it in the installed comparison.
Verify the recommendation
Have the quote record planned occupancy, busy-period demand, room conditions, selected equipment, and intended operation. Ask how startup testing and the household explanation will verify the plan rather than merely showing that the heater turns on.
Do not increase temperature without a qualified plan for settings and fixture protection. A tenant's use needs should be handled through a supported equipment decision, not an undocumented hotter setting.
Your next step is to provide the planned occupancy and draw schedule and request two suitable options with assumptions, complete costs, and expected busy-period performance clearly compared.