Estimate tank water heater size, tankless water heater GPM, first hour rating, peak hot water demand, temperature rise, recovery needs, and household hot water usage for homes, apartments, cabins, and small buildings.
Tank water heater size:
The calculator estimates daily and peak hot water demand, then suggests a common tank size.
Tankless GPM size:
The calculator adds the simultaneous flow from showers, sinks, and appliances to estimate required tankless flow.
First hour rating:
The calculator estimates peak-hour hot water demand and compares it with tank size plus recovery rate.
Capacity check:
The calculator compares your known tank size or tankless capacity to estimated demand.
A water heater size calculator helps estimate whether a tank or tankless heater can keep up with household hot water demand.
It can help compare occupants, bathrooms, simultaneous fixtures, tank size, tankless GPM, recovery rate, first hour rating, temperature rise, and capacity margin.
Your result shows an estimated tank water heater size, tankless GPM need, first hour rating, and capacity margin. This is a planning estimate only. Final water heater selection should consider fuel type, heater efficiency, recovery rate, incoming water temperature, fixture flow rates, local code, venting, electrical or gas supply, and manufacturer sizing charts.
Tank water heaters are often sized from peak-hour demand and first hour rating. Tankless water heaters are usually sized by required GPM at the needed temperature rise.
A common planning range for a family of 4 is often around a 40 to 50 gallon tank, but actual needs depend on showers, appliances, usage habits, and recovery rate.
Add the flow rates of fixtures that may run at the same time, then make sure the tankless heater can provide that GPM at your required temperature rise.
No. This calculator gives a planning estimate. Final water heater sizing should be checked against manufacturer sizing charts and local plumbing, gas, venting, or electrical requirements.