Tankless Water Heater Sizing

Our tankless water heater sizing calculator helps you determine the right GPM (gallons per minute) capacity for your household's hot water demands. Unlike traditional tank water heaters, tankless units heat water on demand, so proper sizing is critical to ensure you never run out of hot water during peak usage.

The calculator considers your simultaneous hot water demands - showers, sinks, dishwashers, and washing machines - along with your local water temperature to determine the temperature rise needed. Cold climate areas with low incoming water temperatures require more powerful units because the heater must work harder to reach your desired output temperature.

This tool is essential for homeowners replacing old tank water heaters, builders specifying equipment for new construction, and anyone asking "what size tankless water heater do I need?" Proper sizing prevents the frustration of lukewarm showers when multiple fixtures run simultaneously.