Scalding and thermal shock entered the plumbing engineers’ vocabulary more than 35 years ago with the advent of water conservation. Showers always were known to increase in temperature when someone activated a flushometer valve, but the temperature increase was minimal when showerheads were unrestricted, flowing at 8- to 10-gpm rates.
When the showerhead flow rate was lowered to 3 gpm, the spike in hot water temperature from the flushing of a water closet spiked to scalding temperatures. Seeing or feeling, an increase in temperature of 35° to 40° F was not uncommon.