Bosch 7736503051 WH27 Tronic 6000 C Whole House Electric Tankless Water Heater

97% thermal efficiency

Compact and lightweight

Electronic flow sensor

Element modulation provides a constant output
  temperature

Filter screen on inlet

New scale prevention technology

Improved temperature stability & control

5 year limited warranty

Specs are based on 240 V. Lesser voltage (220 V
  or 208 V) will result in reduced output

In Canada unit must be wired to a single breaker.
  AE Canada Kit required

The WH36 requires 180 amp circuit protection
  through three 60 amp circuit breakers in the U.S.
  The home MUST have a minimum of 300 amp
  service

The WH27 requires 120 amp circuit protection
  through three 40 amp circuit breakers in
  the U.S. The home MUST have a minimum of
  200 amp service

The WH17 requires 80 amps circuit protection
  through two 40 amp circuit breakers in the U.S.
  The home MUST have a minimum of 150 amp
  service