College Of Product Knowledge: Introduction To Water Heaters
This is an updated version of the product training course introduced by Supply House Times in 1979, authored by Don Arnold.
Since there is an expense to keeping 40 or more gallons constantly heated, there is an advantage to the demand type of heater that uses no storage tank (also called “instantaneous”). In this case, water is heated as required — not stored. The downside here is capacity — demand units generally cannot provide an adequate supply of hot water in installations with heavy demand (unless more than one is installed).