Commercial Water Heater Sizing Calculator

Size a commercial water heater based on peak demand, temperature rise, and recovery requirements.

Inputs

Peak Demand (GPH)

Inlet Water Temp (°F)

Outlet Water Temp (°F)

Recovery Time (hrs)

Tab to move between fields

Results

Recommended Tank Size

140 gal

≈ 6 wheelbarrows

BTU Required

149,940 BTU/hr

Recommended Heater TypeCommercial Tank (Gas/Electric)

First Hour Rating298 GPH

How to Use This Calculator

Enter Peak Demand (GPH), Inlet Water Temp (°F), and Outlet Water Temp (°F).
Set Recovery Time (hrs).
Review Recommended Tank Size (gal) and BTU Required (BTU/hr).
Use Recommended Heater Type and First Hour Rating (GPH) to inform your decision.
Use the chart to visualize the results and explore different scenarios by adjusting inputs.

How the result changes with Peak Demand (GPH)

Peak Demand (GPH)	Recommended Tank Size	BTU Required
1,001	701 gal	750,450 BTU/hr
3,501	2,451 gal	2,624,700 BTU/hr
6,500	4,550 gal	4,873,050 BTU/hr
9,000	6,300 gal	6,747,300 BTU/hr

What each input means

Peak Demand (GPH): Peak hot water demand in gallons per hour during busiest period
Inlet Water Temp (°F): Cold water inlet temperature — varies by geography and season
Outlet Water Temp (°F): Required hot water delivery temperature (140°F typical for commercial)
Recovery Time (hrs): Time in hours to reheat the full tank after depletion

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Peak Demand (GPH) = 200, Inlet Water Temp (°F) = 50, Outlet Water Temp (°F) = 140, Recovery Time (hrs) = 1 = 4 input(s) provided
Calculate Recommended Tank Size
Recommended Tank Size
140 = 140
Calculate BTU Required
BTU Required
149940 = 149940
Calculate Recommended Heater Type
Commercial Tank (Gas/Electric) = Commercial Tank (Gas/Electric)

Engine last updated July 26, 2026. Checked against 2 independently-derived tests — how we verify calculators.

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