Tank, tankless, and heat pump water heater types, sizing by First Hour Rating and recovery rate, continuous vs. demand-controlled recirculation design, and the Legionella/scald temperature-control logic every hot water system depends on.
A hot water system has to solve two problems pulling in opposite directions at once: deliver enough hot water to meet a building's real peak-hour demand, and control temperature tightly enough to be safe from both scalding and Legionella growth — two safety requirements that land on opposite sides of the same thermostat. This module works through tank, tankless, and heat pump water heater selection, the First Hour Rating and recovery rate numbers that actually drive correct sizing, and how continuous versus demand-controlled recirculation trades response time for standby energy loss.
The module closes on the temperature-control logic that resolves the Legionella-versus-scald conflict directly: storing water hot enough to control bacterial growth, then using a master tempering valve to deliver a safer temperature at the fixture — decoupling storage temperature from delivery temperature instead of compromising on one number that satisfies neither requirement.