Tankless units are sized by flow rate (GPM) at a given temperature rise - not by tank gallons. Pick what runs at once and your region; we'll size it so the shower never goes cold.
Hot water target is 120°F. Colder incoming water = bigger temperature rise = a unit works harder.
Summing peak flow…
Required flow
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GPM at peak
Temperature rise
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°F needed
Recommended unit
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Demand worksheet
Regional variancePricing and technical assumptions vary by region. This calculator uses averaged inputs for labor rates, materials, climate zone, and utility costs. Actual figures in your market may differ materially. For a location-specific quote, contact a licensed contractor in your area.