A refresher for the most elementary system of them all - the passive domestic hot water recirculating system.
Trade magazines often run articles discussing the various methods for quickly delivering domestic hot water to a fixture when a faucet is opened. For example, the September 1997 issue of Plumbing Engineer had two articles: One primarily discussed pumped recirculating, the other electric tracer systems. Both articles also briefly mentioned point-of-use systems, which typically consist of an electric heater under a fixture that swiftly delivers hot water to the faucet. Chapter 4, 1989 edition, of the ASPE Data Book only discusses pumped recirculating systems. Chapter 45, 1995 edition, of the ASHRAE Handbook mentions pumped recirculating systems and briefly mentions electric heat traced systems.
The new "Domestic Water Heating Design Manual" developed by ASPE focuses on recirculating and heat traced systems with passing mention of point of use. Each system has advocates. An unbiased engineering analysis may determine one approach to be more suitable in a particular application. But it has been a long time since I have seen a discussion of a most elementary system-the simple, passive domestic hot water recirculating system. No accessories, no other power, no pumps, no controls, nothing additional to maintain.