Commercial Water Heater Sizing Calculator
Use this preliminary calculator page to review domestic hot-water demand, storage capacity, recovery rate, temperature rise, and electric water-heater input for commercial projects.
This tool is intended for preliminary engineering reference only. Final water-heater sizing should be verified using fixture demand, occupancy, operating schedule, manufacturer data, plumbing-code requirements, and project-specific design criteria.
What This Calculator Will Help Estimate
- Peak domestic hot-water demand
- Storage-tank capacity
- Required recovery rate in GPH
- Temperature rise from incoming cold water to storage temperature
- Preliminary electric heating input in kW
- Relationship between storage volume and recovery capacity
Typical Inputs
- Building or occupancy type
- Fixture quantities and usage profile
- Incoming cold-water temperature
- Required hot-water storage temperature
- Peak-use duration
- Available electrical voltage and phase
- Desired storage capacity and recovery time
Basic Formula References
Temperature Rise:
ΔT = Hot-Water Storage Temperature − Incoming Cold-Water Temperature
Heating Energy:
Q = 8.33 × GPH × ΔT
where:
- Q = heating capacity, Btu/hr
- GPH = recovery rate, gallons per hour
- ΔT = water-temperature rise, °F
Electric Input:
kW = Btu/hr ÷ 3,412
Example
If a commercial electric water heater must recover 120 gallons per hour with a temperature rise of 100°F:
Q = 8.33 × 120 × 100
Q = 99,960 Btu/hr
kW = 99,960 ÷ 3,412
Required electric input ≈ 29.3 kW
Important Design Notes
- Storage volume and recovery rate should be evaluated together.
- Commercial kitchens, coffee shops, restaurants, healthcare spaces, and high-demand facilities may require project-specific demand analysis.
- Dishwashers, hand sinks, mop sinks, service sinks, and specialty equipment should be reviewed separately.
- Final equipment selection should be checked against manufacturer recovery tables and electrical requirements.
Download the Excel Calculator
Use the downloadable Excel workbook to estimate domestic hot-water demand, storage capacity, recovery rate, temperature rise, and preliminary electric water-heater input.
This workbook is intended for preliminary design reference. Final water-heater sizing and equipment selection should be verified based on fixture demand, occupancy, operating schedules, manufacturer data, project requirements, and applicable plumbing codes.
Download Water Heater Sizing Calculator
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