Our best overall pick is the Stiebel Eltron Tempra 36 Trend Tankless Water Heater for its 7.5-GPM flow rate, 99 percent efficiency rating, and auto-modulation function.

Alongside these, the tankless or instant hot water heater also appeared ... use both an outdoor and indoor unit (a similar idea to mini-split air conditioners), and although less common, there ...