Commercial Water Heater Sizing Calculator — St. Louis
Estimate peak hot water demand, storage and burner input for your building. We install and replace gas and electric commercial water heaters across the St. Louis metro.
Recommended Sizing
Peak hour demand
20 gal/hr
Storage tank
1 × 50 gal
Gas or electric
Burner input
16k BTU/hr
High-efficiency condensing
Tankless option
1 × 199k
Racked units
Installed cost range
$3,900 – $7,900
Storing above 120°F? A thermostatic mixing valve is required to prevent scalding at fixtures.
Conceptual estimate only — not a bid or quote. Actual cost depends on site conditions, access, code requirements and material pricing. Legacy Plumbing will confirm scope and pricing in writing.
Checking a Water Heater Size Before You Buy
This calculator estimates peak-hour hot water demand from your building type and the number of people, rooms or fixtures it serves, then converts that demand into storage, burner input and tankless equivalents. Storage temperature matters: water stored above 120°F needs a thermostatic mixing valve before it reaches fixtures, and dishwashing or sanitizing loads may need 160°F water at the point of use.
Use the result as a starting point for a conversation, not as a final selection. Venting, gas supply, electrical service, floor space and recirculation all affect which heater fits the room. Our commercial water heater team sizes, replaces and repairs units for restaurants, schools, multifamily and industrial buildings across the St. Louis metro, and can confirm sizing on site before you order equipment.
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