Residential Hot Water Distribution Introduction

Hot water 1The delivery of hot water to faucets, showers, clothes washers, dishwashers, and other hot water-using products in the typical home is an important driver in the water use profile of that home.  In some homes, the design of the plumbing system is such that water is wasted while the user is waiting for hot water to arrive at the end fixture.  This waste may be avoidable with a properly designed plumbing system.  In new homes, the emphasis is upon “structured plumbing”, while in older homes (where it is usually not cost-effective to install a new “structured plumbing” system), certain “add-on” pieces of equipment can sometimes be installed to reduce water waste.

Hot water delivery in the home has an energy component as well.  Energy is wasted in inefficient systems where hot water is wasted or sits in pipes unused.  Emphasis on energy efficiency has led the energy regulatory organizations and utilities to sponsor the study and development of alternative and improved designs for the efficient delivery of hot water in the home.

The Alliance for Water Efficiency has gathered a wide variety of documents relevant to the topic of hot water distribution and use, many of them originating from hot water distribution expert, Gary Klein formerly of the California Energy Commission.

Background Information

For some background on the entire topic and its importance to water efficiency, read this 4-part series of articles on hot water distribution as published in the IAPMO Official Magazine (articles posted by permission from the author):

Klein, G. (2005) Hot Water Distribution Systems - Part 1

Klein, G. (2005) Hot Water Distribution Systems - Part 2

Klein, G. (2005) Hot Water Distribution Systems - Part 3

Klein, G. (2005) Hot Water Distribution Systems - Part 4

World Plumbing Review and PM Engineer magazines covered the topic of structured plumbing in a couple of brief articles by Mr. Klein:

WPR (2008) Structured Plumbing Offers Real Benefits

Klein, G. (2008) Designing Green Hot Water Distribution Systems

A series of articles on High Performance Hot Water Systems first appeared in Official magazine, a publication of the International Association of Plumbing and Mechanical Officials (IAPMO).  It is reprinted here with the permission of the editors and the author.
Part 1:  What Do Consumers Want from Their Hot Water System?   (Third Quarter 2009, Volume 31, Number 5)

Part 2:  Hot Water and How Best to Get It   (Winter 2009, Volume 31, Number 6)

Part 3:  Meeting the One-Cup Challenge   (January/February 2010, Volume 32, Number 1) 

Hot Water Distribution Research

These studies by Oak Ridge National Laboratory conducted with the City of Palo Also and with the California Energy Commission cover hot water recirculating and distribution systems:

Ally, M.R., (2002) Water and Energy Savings using Demand Hot Water Recirculating Systems in 5 Residential Homes

Wendt, R. (2004) Evaluation of Residential Hot Water Distribution Systems by Numeric Simulation

In 2002, the Santa Clara Valley Water District completed a pilot study of hot water distribution systems installed in residential dwellings.

De La Piedra, J. (2002) Hot Water Re-circulation Pilot Study

In 2002, the National Association of Home Builders Research Center modeled various plumbing system configurations in residential dwellings and simulated conditions of use.  This 67-page report contains a great deal of data on hot water use in the home and can be a valuable resource for further investigation of water efficiency opportunities.

NAHBRC (2002) Domestic Hot Water System Modeling for the Design of Energy Efficient Systems

More recently, Lawrence Berkeley National Laboratories issued two short pieces on (1) roadmapping a study to improve residential hot water distribution systems and (2) estimating water and energy losses within such systems:

Lutz, J. (2004) Feasibility study and roadmap to improve residential hot water distribution systems

Lutz, J. (2005) Estimating Energy and Water Losses - Residential Hot Water Distribution

Klein’s article (2 parts) for the Plumbing Systems & Design Magazine (official magazine of the American Society of Plumbing Engineers) also covers the design aspects of structured plumbing and its importance in achieving water and energy efficiency.

Klein, G. (2004) Hot Water Distribution Systems - Part 1

Klein, G. (2004) Hot Water Distribution Systems - Part 2

The Metropolitan Water District of Southern California funded a study of the Laing hot water on-demand system installed in San Diego residential dwellings in 2005.

Burr-Rosenthal, K. (2005) San Diego Instant Hot Water Delivery System Pilot Project

In the same year, the California Energy Commission (CEC) released a comprehensive report titled "Hot Water Distribution System Research - Phase 1" (200p). This report contains extensive data on all types of piping designs and water delivery systems.

CEC (2005) Hot Water Distribution System Research - Phase 1

Building Sciences Corporation recently reported on their evaluation of the water savings achieved with an on-demand hot water system in one home.

Building Science Corp. (2005) Wait and Waste Testing of D.R. Horton Beta Home

This 2006 article in Home Energy magazine also focused on the hot water topic, describing the demand system pumping design for homes and the water and energy savings that can be captured from such systems.

Acker, L. (2006) Benefits of Demand Controlled Pumping

Installation of a Hot Water Demand system was a part of a 2007 case study report on a “real world” application in an Australian home.

ReNew (2007) An Energy and Water Odyssey 

In 2006, the California Urban Water Conservation Council conducted a summary evaluation of the potential for efficient hot water distribution systems to become a California Best Management Practice.

Koeller, J. (2007) Residential Hot Water Distribution PMBP

Do tankless water heaters save water? The question of wastage from gas-fired tankless heaters is examined in this 2008 study from Australia:

Szann, A. (2008) Water Wastage of Instantaneous Gas Water Heaters - Australia 

Other Resources

Koeller, J (2008) Danger in the Shower - 2008 Forum Looks at Hot Water

GBS (2007) Supply and Demand Side Water and Energy Efficiency Opportunities

Davis Energy Group (2006) Documentation of Hot Water Distribution Systems in 60 Calif Production Homes