EcoSmart 24-kW Self Modulating 4.6 GPM Electric Tankless Water Heater for $351.90 shipped. Here is a screenshot for your reference. EcoSmart Electric Tankless Water Heaters (a.k.a. Instantaneous On Demand Water Heaters) provide endless hot water on demand and only as needed. It is configured for climates where incoming water temperature can reach as low as 37 degrees Fahrenheit. Most places have it for about $500.