Why Electric Tankless Water Heater Installation Requirements Matter Before You Buy Electric tankless water heater installation requirements are more demanding than most homeowners expect — and getting them wrong can mean a failed inspection, a voided warranty, or a serious electrical hazard. Here is a quick summary of what you need before installation: Requirement What You Need Voltage 240V dedicated supply (most whole-house units) Amperage draw 51 amps (12.2 kW) up to 133 am