Residential power here for single family homes -- the type which could reasonably do what you suggest -- is almost always single phase 120/240V. As an upper bound, let's consider 400A service. (Most homes have services smaller than 400A, and even 400A service is typically delivered to a pair of smaller panels to keep conductor and busbar sizes manageable.) Such heaters would be considered continuous loads, reducing the 400A service to 320A of current. Resistive heaters are a linear load, so we can multiply 240V * 320A to get 76.8 kW at maximum.

Hitting 76 kW is wildly impractical. Exceeding 100 kW is nonsense.