A standard 50 gallon gas tank style water heater has a 40000 btu burner, which heats about 35 gallons per hour. By comparison, an average gas fired tankless water heater has an 180000 btu burner, which will heat 4 gallons per minute (GPM) in our climate here in the Pacific Northwest, or 240 gallons per hour. More powerful tankless models will heat even more. An average electric tank style water heater can only heat 18 gallons per hour.
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