Electric tankless water heater — the panel is the constraint

A whole-home electric tankless unit needs multiple big circuits (~113 A) and often a 200 A service — the panel, not the plumbing, is the limit.

Two breaker panels compared. A tank water heater uses one 30 A double-pole breaker. A whole-home electric tankless unit (27 kW) needs three 40 A double-pole breakers totaling about 113 amps, filling much of the panel. A note: 27 kW divided by 240 V is about 113 A across three circuits, requiring a 200 A service. The plumbing is easy; the electrical load is the real limit. — Source: Manufacturer spec sheets (Rheem, Stiebel Eltron, EcoSmart)

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Two breaker panels compared. A tank water heater uses one 30 A double-pole breaker. A whole-home electric tankless unit (27 kW) needs three 40 A double-pole breakers totaling about 113 amps, filling much of the panel. A note: 27 kW divided by 240 V is about 113 A across three circuits, requiring a 200 A service. The plumbing is easy; the electrical load is the real limit.

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