Estimate hot water demand for homes, apartments, cabins, and small buildings. Calculate simultaneous fixture flow, peak hot water demand, daily hot water use, first hour demand, tankless GPM need, and tank water heater capacity requirements.
Peak demand:
The calculator multiplies simultaneous hot water flow by peak use time.
Daily demand:
The calculator estimates daily hot water usage from occupants and gallons per person per day.
Tankless demand:
The calculator estimates required tankless GPM from simultaneous fixture flow and safety factor.
First hour demand:
The calculator compares peak demand with known tank size and recovery rate.
A hot water demand calculator helps estimate whether a tank or tankless water heater can handle expected hot water use.
It can help compare simultaneous flow, peak gallons, daily use, tankless GPM, first hour demand, recovery rate, and capacity margins.
Your result shows estimated peak hot water demand, daily hot water demand, tankless GPM requirement, and first hour demand. Use this as a planning estimate only. Final water heater sizing should account for fixture flow rates, recovery rate, incoming water temperature, fuel type, heater efficiency, local code, and manufacturer sizing charts.
Hot water demand is the amount of hot water needed for fixtures and appliances during a period of use. It can be measured in gallons, gallons per minute, or first hour demand.
Add the flow rates of fixtures running at the same time, then multiply by how long they run during the peak period.
Temperature rise shows how much the heater must warm incoming water. Colder incoming water requires more heating power.
No. This calculator gives a planning estimate. Final sizing should be checked against actual usage, fixture flow rates, local code, and water heater manufacturer charts.