Disaggregating Hot Water 

Use and Predicting Hot Water 

Waste in Five Test Homes

Hugh Henderson and Jeremy Wade

ARIES Collaborative

April 2014
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iii

Disaggregating Hot Water Use and Predicting 

Hot Water Waste in Five Test Homes

Prepared for:

The National Renewable Energy Laboratory

On behalf of the U.S. Department of Energy’s Building America Program 

Office of Energy Efficiency and Renewable Energy

15013 Denver West Parkway 

Golden, CO 80401 

NREL Contract No. DE-AC36-08GO28308 

 Prepared by: 

Hugh Henderson and Jeremy Wade 

ARIES Collaborative 

The Levy Partnership, Inc.

1776 Broadway, Suite 2205 

New York, NY 10019 

NREL Technical Monitor: Michael Gestwick

Prepared under Subcontract No. KNDJ-0-40347-03

April 2014
iv

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v 

Contents

List of Figures ............................................................................................................................................ vi

List of Tables ............................................................................................................................................ viii

Definitions................................................................................................................................................... ix

Executive Summary.................................................................................................................................... x

1 Problem Statement............................................................................................................................... 1

1.1 Introduction .....................................................................................................................1

1.2 Background .....................................................................................................................1

1.3 Relevance to Building America’s Goals .........................................................................2

1.4 Cost Effectiveness ...........................................................................................................3

1.5 Tradeoffs and Other Benefits ..........................................................................................3

2 Experiment ............................................................................................................................................ 4

2.1 Research Questions .........................................................................................................4

2.2 Technical Approach ........................................................................................................4

2.3 Measurements and Data logging Equipment ...................................................................5

3 Analysis Approach ............................................................................................................................... 9

3.1 Typical Hot Water Draw Events .....................................................................................9

3.2 Classifying Draw Events ...............................................................................................12

3.3 Errors in Classifying Draw Events ................................................................................15

4 Pre-Retrofit or Baseline Results ....................................................................................................... 18

4.1 Classifying Draw Events at Each Site ...........................................................................18

4.2 Summary of Cross-Site Performance ............................................................................28

4.3 Assessing the Impact of Threshold Level .....................................................................31

4.4 Propagation of Measurement Errors to the Determination of “Usefulness” .................36

5 Impact of Retrofits.............................................................................................................................. 37

5.1 Impact of Tankless Retrofit at Site 3 (Group 2) ............................................................37

5.2 Impact of Distribution Retrofit at Site 1 (Group 3) .......................................................44

5.3 Impact of Distribution Retrofit at Site 2 (Group 3) .......................................................47

6 Conclusions ........................................................................................................................................ 51

6.1 Disaggregation and Useful Hot Water Delivery ...........................................................51

6.2 Retrofit Impacts .............................................................................................................51

6.3 Addressing the Research Questions ..............................................................................52

6.4 Lessons and Recommendations .....................................................................................53

References................................................................................................................................................. 55

Appendix A: Literature Review................................................................................................................ 56

Appendix B: Site Descriptions................................................................................................................. 68
vi 

List of Figures

Figure 1. Schematic showing monitored points collected at a typical test site................................... 6

Figure 2. Hot water draw at master bath shower—December 2, 2012................................................. 10

Figure 3. Hot water draw at master bath sink—December 2, 2012 ...................................................... 11

Figure 4. Hot water draw at kitchen sink—December 2, 2012.............................................................. 12

Figure 5. Hot water draw that was unclassified, Site 1, December 5, 2012......................................... 15

Figure 6. Hot water draw that was misclassified, Site 1, December 15, 2012..................................... 16

Figure 7. Hot water draw that was misclassified, Site 4, December 27, 2012..................................... 17

Figure 8. Summary of classified draw events, Site 1, December 1 to April 2: 0–40 gal .................... 19

Figure 9. Summary of classified draw events, Site 1, December 1 to April 2: 0–5 gal ...................... 19

Figure 10. Summary of classified draw events, Site 2, December 14 to May 19: 0–40 gal................ 20

Figure 11. Summary of classified draw events, Site 2, December 14 to May 19: 0–5 gal.................. 21

Figure 12. Summary of classified draw events, Site 3, December 13 to March 22: 0–40 gal ............ 22

Figure 13. Summary of classified draw events, Site 3, December 13 to March 22: 0–5 gal .............. 22

Figure 14. Summary of classified draw events, Site 4, December 26–30, 2012: 0–40 gal ................. 24

Figure 15. Summary of classified draw events, Site 4, December 26–30, 2012: 0–5 gal ................... 24

Figure 16. Monthly breakdown of hot water use (Site 4) ...................................................................... 25

Figure 17. Monthly variation of “usefulness” by end use (Site 4) ....................................................... 25

Figure 18. Summary of classified draw events, Site 5, December 14 to June 30: 0–40 gal .............. 26

Figure 19. Summary of classified draw events, Site 5, December 14 to June 30: 0–5 gal ................ 27

Figure 20. Monthly breakdown of hot water use (Site 5) ...................................................................... 27

Figure 21. Monthly variation of “usefulness” by end use (Site 5) ....................................................... 28

Figure 22. Breakdown of hot water use by end use .............................................................................. 29

Figure 23. Breakdown of daily hot water use by end use..................................................................... 29

Figure 24. Portion of hot water deemed as useful from each end use................................................ 30

Figure 25. Impact of threshold temperature on “usefulness” at each fixture (Site 1) ....................... 32

Figure 26. Impact of threshold temperature on “usefulness” at each fixture (Site 2) ....................... 33

Figure 27. Impact of threshold temperature on “usefulness” at each fixture (Site 3) ....................... 34

Figure 28. Impact of threshold temperature on “usefulness” at each fixture (Site 4) ....................... 35

Figure 29. Impact of threshold temperature on “usefulness” at each fixture (Site 5) ....................... 36

Figure 30. Comparing pre- and post-retrofit periods (Site 3) ............................................................... 37

Figure 31. Plot showing variation of useful water draw percentage across period (Site 3) ............. 38

Figure 32. Typical water draw—conventional tank and old washing machine .................................. 41

Figure 33. Typical water draw—tankless and old washing machine................................................... 41

Figure 34. Typical water draw—tankless and new efficient washing machine .................................. 42

Figure 35. Typical kitchen sink water draw—conventional tank ......................................................... 43

Figure 36. Typical kitchen sink water draw—tankless.......................................................................... 43

Figure 37. Trunk and fixture temperatures during recirculation pump operation (Site 1 EST) ........ 44

Figure 38. Plot showing variation of useful water draw percentage across period (Site 1) ............. 45

Figure 39. Plot showing variation of water use across monitoring period (Site 2)............................ 47

Figure 40. Daily system efficiency as a function of hot water use (Site 2) ......................................... 48

Figure 41. Plot showing thermal input versus thermal output (Site 2)................................................ 49

Figure 42. Plot showing variation of useful water draw percentage across period (Site 2) ............. 49

Figure 43. Comparing various hot water use profiles from Lutz et al. (2008). Blue bars are 

the results from Lutz et al.; red bars are from ASHRAE 90.2; yellows bars are from 

Becker (1990) ...................................................................................................................................... 60

Figure 44. Plot from Magusson (2009) comparing direct measurements of hot water flow events 

(square) to Aquacraft results; Aquacraft method was good but did have some error. .............. 61

Figure 45. Site 1 pipe layout, pipe length, and sensor location........................................................... 69

Figure 46. GeoSprings HPWH.................................................................................................................. 71

Figure 47. Bell & Gossett ecocirc recirculation pump installed on the return line to the domestic 

cold water inlet................................................................................................................................... 71

Figure 48. 1⁄2 in. PEX was used for the recirculation return line with 1⁄2-in. copper used from the 

recirculation pump to the cold water tie-in...................................................................................... 71
vii 

Figure 49. Return line from kitchen spur and half-bath sink with ball valve and check valve 

visible. This ball valve is almost completely closed allowing more recirculation from the 

kitchen spur than the main trunk..................................................................................................... 72

Figure 50. Kitchen piping in crawl space with return line and kitchen sink branch visible. Ball 

valve at this location is fully open allowing for full recirculation when the pump is on............. 72

Figure 51. Data logger enclosure with space temperature and relative humidity sensors installed 

on top................................................................................................................................................... 72

Figure 52. Cold water piping with flow meter and separate HPWH and boiler branches visible ..... 72

Figure 53. Boiler control board showing current switches measuring boiler zone statuses ........... 73

Figure 54. Dehumidifier in newer basement section with status and power being measured. ........ 73

Figure 55. HPWH power is measured inside this enclosure. Inside are the CTs and power 

transducer. .......................................................................................................................................... 73

Figure 56. Typical surface mount thermocouple installation. Thermal paste, thermocouple, 

foam insulation tape, and cable ties if necessary........................................................................... 73

Figure 57. Site 2 floor plan ....................................................................................................................... 75

Figure 58. Site 2 pipe layout and sensor location ................................................................................. 76

Figure 59. Original standard gas storage water heater......................................................................... 78

Figure 60. New condensing gas storage water heater installed during retrofit. ................................ 78

Figure 61. IMAC gas meter with pulser to measure gas use. ............................................................... 78

Figure 62. Taco SmartPlus recirculation pump installed on hot water supply with remote 

temperature sensor............................................................................................................................ 79

Figure 63. Flow meter and cold water temperature after retrofit ......................................................... 79

Figure 64. Current switch used to measure water heater status ......................................................... 79

Figure 65. Site 3 pipe layout and sensor location ................................................................................. 81

Figure 66. Site 3 floor plan ....................................................................................................................... 82

Figure 67. Original storage water heater location ................................................................................. 84

Figure 68. New tankless water heater from retrofit ............................................................................... 84

Figure 69. IMAC gas meter with pulser................................................................................................... 84

Figure 70. Flow meter and laundry trunk temperature.......................................................................... 84

Figure 71. Showing direction of hot water flow from tankless water heater ...................................... 85

Figure 72. Shows direction of hot water flow after retrofit. The old hot water supply tied into 

the pipe at the elbow circled in red and was a vertical drop to the old water heater.................. 85

Figure 73. Shows lengthened cold water supply piping...................................................................... 85

Figure 74. Site 4 floor plan ....................................................................................................................... 86

Figure 75. Site 4 Pipe Layout ................................................................................................................... 87

Figure 76. Site 5 Floor Plan...................................................................................................................... 89

Figure 77. Site 5 Pipe Layout and Sensor Location .............................................................................. 90

Unless otherwise indicated, all figures were created by ARIES.
viii

List of Tables

Table 1. Five Field Test Sites With Detailed Monitoring ......................................................................... 5

Table 2. Data Points Monitored at Typical Site ........................................................................................ 7

Table 3. Logic Table for Fixture and Trunk Temperatures (Site 1) ...................................................... 13

Table 4. Logic Table for Fixture and Trunk Temperatures (Site 2) ...................................................... 13

Table 5. Logic Table for Fixture and Trunk Temperatures (Site 3) ...................................................... 14

Table 6. Logic Table for Fixture and Trunk Temperatures (Site 4) ...................................................... 14

Table 7. Logic Table for Fixture and Trunk Temperatures (Site 5) ...................................................... 14

Table 8. Summary of Results for Site 1, December 1, 2012 to April 2, 2013 (123 Days).................... 18

Table 9. Summary of Results for Site 2, December 14, 2012 to May 19, 2013 (157 Days) ................. 20

Table 10. Summary of Results for Site 3, December 13, 2012 to March 22, 2013 (98 Days) ............. 21

Table 11. Summary of Results for Site 4, December 10, 2012 to June 30, 2013 (202 Days).............. 23

Table 12. Summary of Results for Site 5, December 14, 2012 to June 30, 2013 (198 Days).............. 26

Table 13. Summary of Classification Statistics for Five Sites.............................................................. 31

Table 14. Impact of Threshold Temperature on Determining “Usefulness” (Site 1).......................... 31

Table 15. Impact of Threshold Temperature on Determining “Usefulness” (Site 2).......................... 32

Table 16. Impact of Threshold Temperature on Determining “Usefulness” (Site 3).......................... 33

Table 17. Impact of Threshold Temperature on Determining “Usefulness” (Site 4).......................... 34

Table 18. Impact of Threshold Temperature on Determining “Usefulness” (Site 5).......................... 35

Table 19. Propagation of Measurement Errors to Error in Determination of “Usefulness”.............. 36

Table 20. Variation of Useful Water Draw Percentage Across Period (Site 3).................................... 38

Table 21. Impact of Retrofit on Events and Hot Water Use (Pre-Retrofit = Tank; Post-Retrofit = 

Tankless) ............................................................................................................................................. 39

Table 22. Comparing Water Draws for Different Water Heaters and Washing Machines.................. 40

Table 23. Comparing Kitchen Water Draws With Different Water Heaters ......................................... 42

Table 24. Variation of Useful Water Draw Percentage Across the Period (Site 1) ............................. 45

Table 25. Impact of Retrofit on Events and Total Hot Water Use at Site 1 (Pre-Retrofit; PostRetrofit)................................................................................................................................................ 46

Table 26. Variation of Useful Water Draw Percentage Across Period (Site 2).................................... 50

Table 27. Impact of Retrofit on Events and Total Hot Water Use (Site 2) (Pre-Retrofit; PostRetrofit)................................................................................................................................................ 50

Table 28. Summary of Residential Recirculation Products on the Market ......................................... 58

Table 29. Cost Breakdown of Water Heater Install and Distribution Retrofit (Site 1) ........................ 68

Table 30. Site 1 Data Point List and Descriptions ................................................................................. 70

Table 31. Cost Breakdown of Water Heater Install and Distribution Retrofit (Site 2) ........................ 74

Table 32. Site 2 Data Point List and Descriptions ................................................................................. 77

Table 33. Cost Breakdown of Water Heater Installation (Site 3) .......................................................... 80

Table 34. Site 3 Data Point List and Descriptions ................................................................................. 83

Table 35. Site 4 Data Point List and Descriptions ................................................................................. 88

Table 36. Site 5 Data Point List and Descriptions ................................................................................. 91

Unless otherwise indicated, all figures were created by ARIES. 
ix

Definitions

ARIES Advanced Residential Integrated Energy Solutions Collaborative Building 

America team

ASHRAE American Society of Heating, Refrigerating, and Air Conditioning 

Engineers 

AWWARF American Water and Wastewater Association Research Foundation

BA Building America

CDH CDH Energy Corporation, ARIES team member

CEC California Energy Commission

DHW Domestic hot water

ECM Electronically commutated motor

EF Energy factor

EPA Environmental Protection Agency

GTI Gas Technology Institute

Hot Water Use Volume flow rate of hot water

HPWH Heat pump water heater

HWSIM Hot Water Simulation (software)

LBNL Lawrence Berkeley National Laboratory

NREL National Renewable Energy Laboratory

NYSERDA New York State Energy Research and Development Authority

PEX Cross-linked polyethylene (piping)

RECS Residential Energy Consumption Survey

REUWS Residential End Uses of Water Survey

TRNSYS Transient System Simulation (software)
x 

Executive Summary

Water heating is the second largest energy expenditure in homes in the Northeast, after space 

heating. Several energy-efficient water heating options are currently available, including more 

efficient tanks, tankless systems, and others. While it is important to make the equipment (or 

“plant”) in a residential hot water system more efficient, the hot water distribution system also 

affects overall system performance and energy use. Energy wasted in heating water that is not 

used; that is, heat lost through piping and previously heated water that runs down the drain 

during a hot water draw while waiting for an acceptable temperature, is estimated to be on the 

order of 10%–30% of total domestic hot water energy use.

This project seeks to quantify the magnitude of hot water waste in existing Northeastern homes. 

This Building America (BA) project expands the field testing effort at several homes that are 

being tested as part of a water heating evaluation project sponsored by the New York State 

Energy Research and Development Authority). The BA portion of the work expanded the 

monitoring effort to focus on measuring the amount of hot water waste in five homes. The five 

monitored test sites include: 

• Group 1—two baseline (or control) sites 

• Group 2—one site where a conventional hot water tank was changed to a tankless system

• Group 3—two sites where the water heater and distribution system will be changed. 

The last three test sites (Groups 2 and 3) will be monitored both before and after the changes are 

implemented.

Data logging equipment was installed at the five houses near Syracuse, New York and data 

collection commenced in December 2012. Data collection gathered 15-minute data as well as 

data collected at 5-second intervals during each hot water draw event. Procedures were 

developed to classify or assign each hot water use event to a fixture using temperature sensors 

installed on the distribution piping. This process was able to classify less than half of the water 

draws but typically about 95% of the hot water volume in each home. This classification process 

was achieved without the need to install flow meters for each fixture (which would have been 

cost-prohibitive and more disruptive to homeowners). The average number of events at each 

home ranged from 26/day to 180/day. Average hot water use ranged from 34 to 115 gal/day. 

We also used pipe temperature sensors to determine the portion of hot water draw that was 

deemed useful. A temperature of 90°F at the fixture piping was selected as the threshold for 

gauging usefulness (other thresholds were also evaluated). The amount of hot water deemed 

useful ranged from a low of 75% ± 5% at Site 4 to a high of 91% ± 2% at Site 5—thus implying 

9%–25% waste. Site 4 may have had a lower useful percentage in part be due to the fact that the 

sensors installed on cross-linked polyethylene (PEX) piping may have had a slower thermal 

response. As expected, the amount of hot water waste was found to be higher for bathroom and 

kitchen sinks and lowest for showers and washing machine draws. Overall, the probable error in 

the determination of “usefulness” was estimated to be ± 2% for Sites 1, 2, 3, and 5 with copper 

piping and ± 5% at Site 4 with PEX piping. 
xi

Three of the houses were retrofitted with water heaters (Group 2) and in some cases additional 

distribution improvements were implemented as well (Group 3). 

At Site 3 (Group 2) a new tankless water heater was installed to replace a conventional gas-fired 

tank. The homeowners cut the number of water draws in half, but the volume of hot water use 

stayed about the same. The overall percentage of useful hot water delivered to the fixtures 

decreased from 90%–91% before the retrofit to 84%–86% with the tankless unit. The change is 

mostly explained by the 40-second startup delay for the tankless unit from a cold start. The 

homeowners at this site also purchased a high efficiency washing machine a few weeks after the 

retrofit. The pulsing nature and low volume of the appliance’s hot water draw cycles resulted in 

virtually no useful hot water being delivered to the appliance with the tankless unit. We also 

noticed unexplained burner cycling with the tankless unit at times, even though the flow rate was 

well above the cutout flow of 0.26 gpm. 

Site 1 (Group 3) had both a new heat pump water heater installed as well as distribution system 

improvements. The hot water supply line was shortened by 177 in. since the new location was 

closer to the center. A recirculation pump was installed that included an internal time clock as

well as an internal thermostat. The pump pulled return water from two remote locations on the 

first floor (the kitchen and the half bath). On average the pump ran about 3 minutes/day to prime 

the hot water lines during periods when hot water usage was expected to be high. The useful 

portion of hot water delivered increased from 82% before the retrofit to 91% after. The largest 

improvement was in the kitchen area. More modest improvements for other fixtures (not served 

by the pump) were also noted due to the shorter supply trunk (i.e., 28%–35% for the master sink 

and 49%–66% for the bath 2 sink). 

Site 2 (Group 3) had a new condensing water heater installed with a Taco SmartPlus 

recirculation pump. The pump was set to operate in the smart mode where it anticipates hot 

water use based on the previous 7-day operating pattern. The pump was observed to operate 

about 200 minutes/day, or about 14% of the time. This excessive runtime resulted in significant 

thermal losses. While this water heater unit was observed to have an effective energy factor of 

0.85 in the laboratory, it operated at 40%–70% efficiency at this site depending on daily hot 

water use. The poor field performance of this system was linked to increased thermal standby 

losses of 15–16 MBtu/day due to pump operation. The pump had no perceptible impact on the 

amount of hot water use at the site; however, the large variations in hot water use throughout the 

pre- and post-retrofit periods may have obscured the impact of the retrofit. 

Overall, there were some indications of improved hot water “usefulness” at the fixture for one of 

the two retrofitted sites. However, no direct reduction in hot water use or energy use was 

measured. Therefore, no energy cost savings were observed to offset the installed cost of $500–

$1,000 to implement these distribution system improvements. Monitoring is expected to continue 

beyond this initial test period to confirm these findings. 
1 

1 Problem Statement

1.1 Introduction

Water heating is the second largest energy expenditure in existing homes in the Northeast, 

after space heating (RECS 2005, Table 13). Historically, efforts to improve residential 

efficiency have focused on space conditioning, often neglecting water heating improvements. 

Several new or recently refined water heating technologies are now available on the market 

including: solar water heaters; gas-fired, tankless units; and heat pump water heaters

(HPWHs). Tax credits are currently available for some of these systems that are expected to 

boost consumer interest. 

Current U.S. Department of Energy rating procedures to determine the energy factor (EF), or 

efficiency, of these systems may be poor indicators of actual energy use, in part because the 

amount and timing of water use greatly impacts the performance and relative efficiency 

ranking of these systems. Better information is needed to help consumers, manufacturers, and 

installers understand the efficiency, costs, and environmental impacts of both new and 

conventional domestic hot water (DHW) systems for retrofit and new construction 

applications. 

While it is important to make the equipment or “plant” in a residential hot water system 

efficient, the hot water distribution system also affects overall system performance and 

energy use. Energy wasted in heating water that is not used—that is, heat lost through piping 

and heated water that runs down the drain during a draw while waiting for an acceptable hot 

temperature—is estimated to be on the order of 10%–30% of total DHW energy use (Klein 

2006; Chinery 2006; Lutz 2005; Hendron et al. 2009). 

1.2 Background

Several technologies and approaches have been identified to reduce hot water distribution 

system losses and waste, including:

• Floor plans that organize or “stack” kitchen and bathrooms to minimize the length of 

hot water piping runs 

• Structured plumbing arrangements that use trunk/branch arrangements 

• Recirculation pumps that operate on demand to prime trunk piping (by pumping 

water back to the DHW tank using either a dedicated return line or a cold water line).

These approaches and technologies have been successfully applied and demonstrated in gut 

rehab or new construction projects, mostly in California and other western states. Less effort 

has been aimed at determining which approaches are most appropriate for existing buildings 

and DHW retrofit applications in northeastern homes—the focus of this effort. Existing 

northeastern homes differ from western homes in ways that may affect the costs, efficacy, 

and practicality of DHW distribution retrofit approaches. For example, many northeastern 

homes are significantly older than their western counterparts. Older plumbing systems may 

contain galvanized steel, cast iron, or even lead pipes that are less common in newer western 

homes. Likewise, older plumbing designs may still be in use in older northeastern homes. 

Increased age also increases the likelihood that plumbing has been affected by past 
2 

renovations, complicating the system, and by corrosion that can restrict flow, especially in 

iron and steel pipe. Northeastern homes are far more likely to have basements where the 

piping is easily accessible (compared to under slabs or in the attic in the West), but exposed 

to colder temperatures if those basements are unheated. Differences in home layout also 

affect DHW distribution: Western homes tend to be shorter and more spread out, while older 

northeastern homes, especially in towns and urban areas, are often narrow and tall with baths 

and kitchens stacked upon each other. Furthermore, colder weather in the Northeast 

compared to California may lead to different DHW consumption patterns by occupants—

both in the amount of DHW used per person and the DHW comfort temperature. 

A comprehensive literature review is included in Appendix A. 

Advanced Residential Integrated Energy Solutions (ARIES) team partners New York State 

Energy Research and Development Authority (NYSERDA), CDH Energy Corp. (CDH), and 

the Syracuse Center of Excellence are implementing a project that includes laboratory tests 

and field measurements in 18 New York State homes to understand the energy costs and 

environmental impacts of both high-efficiency and conventional DHW systems. This 

Building America (BA) effort expands the scope of the field research component to include a 

characterization of DHW end uses and an assessment of DHW distribution retrofit 

approaches in a subset of these homes. 

In the NYSERDA-funded effort, the team is monitoring eight water heating systems in a 

laboratory test setup at the Syracuse Center of Excellence. The team has also recruited 18 

field test homes. Data will be collected on the water heating systems of the field test homes 

to understand detailed water heater performance as well as to quantify hot water use and

energy use patterns. The plan calls for detailed field monitoring (to determine fuel input, 

equipment efficiency and energy balance) at two of the field sites, with overall hot water use 

(or volume flow rate) monitoring at the remaining 16 sites.

1.3 Relevance to Building America’s Goals

This project seeks to quantify the energy losses and waste associated with hot water 

distribution systems in existing homes in the Northeast. Our goal is to quantify the energy 

associated with waste and losses due to distribution system piping size and layout. While The 

National Renewable Energy Laboratory (NREL) and other BA teams have quantified these 

losses in homes in Colorado (Magnusson 2009) and California (Hendron et al. 2009), we 

believe that no testing has been completed in existing northeastern homes.

Once losses are quantified, we will evaluate various options to mitigate these losses and 

quantify the impact of any improvements. The ultimate goal of this effort is to develop 

guideline documents that recommend retrofit approaches that can be implemented as part of 

the traditional water heater replacement, millions of which are completed every year in the 

United States. 
3 

This work will contribute to the eventual development of the following planned BA

guidelines for existing homes:

• Replacing water heaters 

• Reducing hot water tank and pipe losses. 

1.4 Cost Effectiveness

For any water heating system improvements to be cost effective, they must fit into normal 

business practices. Water heater replacements are implemented by plumbers who normally 

replace the units on an emergency basis with little or no notice. In this market, it is important 

to have high efficiency water heaters available “on the truck” or at least at the distributor for

each installation visit. 

We seek to develop a standard set of modifications or improvements that can be implemented 

as part of a typical water heater installation. Integrating distribution system improvements 

with a water heater installation is a necessary condition to ensure the improvements can be 

cost-effectively implemented. 

Klein (2005) reports that the incremental cost of installing demand recirculation pumps, 

insulation, and other changes in new construction are on the order of $500. Some more recent 

cost estimates are closer to $1,000. If costs for distribution retrofits in the Northeast are in the 

$500–$1,000 range and assuming 15% savings on annual hot water cost of $400/year, the 

simple payback would be approximately 8–16 years. Integrating this measure with a water 

heater replacement can potentially make it even more cost effective. Costs and savings will 

be measured for the retrofits to be conducted at two sites. 

1.5 Tradeoffs and Other Benefits

Our goal is to quantify the energy savings and other impacts of various distribution system 

improvements. The ultimate goal is to gather sufficient performance data so that this measure 

can be compared and ranked relative to the other energy efficiency improvements normally 

implemented in a residence.

In addition to energy efficiency, distribution improvements can enhance homeowner 

convenience and comfort by speeding up the delivery of hot water to each end use. 

Homeowners are often frustrated by the amount of time they must wait for hot water to reach 

a sink or shower. 
4 

2 Experiment 

2.1 Research Questions

This project seeks to answer the following research questions: 

• What is the magnitude of hot water waste for existing homes in the Northeast, 

considering a variety of water heating systems (i.e., tankless and storage tank)? 

• What constitutes a “typical” distribution system in the Northeast? How does it 

compare to systems in other regions of the United States? 

• What improvements or remediation can be cost-effectively implemented in a DHW 

retrofit to reduce hot water waste and energy use, focusing on hot water system 

configurations commonly found in older single-family homes in the Northeast? 

2.2 Technical Approach

The NYSERDA-funded field monitoring effort was expanded at five field test sites in order 

to collect more detailed data on the hot water distribution system by placing temperature 

sensors on hot water distribution lines and enhancing the data logger capabilities. These 

enhancements provided the means to assign hot water draw events to each fixture using a 

flow disaggregation method using temperature rise similar to that discussed by Barley et al. 

(2010) and Magnusson (2009). This flow disaggregation method allows flows to be 

characterized at the fixture level with a single flow meter installed on the DHW system. It 

avoids the installation of flow meters at each fixture in each home. Installation of multiple 

flow meters would have been costly and very disruptive for homeowners. 

The limitations of this technique, as noted in the Results section of this report, include 

difficulty in classifying very brief events, very low flows, and simultaneous flows at multiple 

fixtures. Nevertheless, these unclassified events represented only a small portion (less than 

10%) of total hot water used and so are not significant sources of DHW distribution energy 

waste. Ongoing work will include benchmarking a sample of events using this technique 

against known end-use draws to confirm this analysis.

The enhanced data logger was programmed to collect event-based data required for this 

disaggregation method. These five enhanced field test sites include three groups of homes 

(Table 1). 

At Group 1 (two sites) no changes were made to the existing systems; these homes represent 

baseline performance to disaggregate water draws and estimate the magnitude of losses and 

water waste. 

At Group 2 (one site) the water heating equipment was replaced with new, high performance 

equipment (e.g., a tankless system) in order to detect any changes in distribution system 

performance.

At Group 3 (two sites) a new, high performance water heater was installed and cost-effective 

distribution system improvements implemented. 
5 

Data collection began at the five sites in December 2012. At the Group 2 and Group 3 field 

test sites data were collected both before and after water heater installation. The retrofits at 

the Group 2 and Group 3 sites were implemented in March, April, and May 2013. This report 

includes post-retrofit data through June 2013. 

Table 1. Five Field Test Sites With Detailed Monitoring

This report summarizes the data collected from the five sites.

2.3 Measurements and Data Logging Equipment

At the five BA test sites, a monitoring system was installed to measure: 

• The energy content of the delivered hot water from the water heater

• The fuel and/or electric input into the water heater (post-retrofit only). 

In addition we measured: 

• Key temperatures in the trunks and branches leading to each fixture

• The environmental conditions (air temperature) near the water heater and piping (the 

relative humidity was measured where the system is an HPWH) 

• Flue gas temperature for combustion appliances 

• Runtime or status of each component (e.g., resistance elements, fans, pumps). 

Group Site System 

Changes

Data Collection 

Start

Date of 

Retrofit

Group 3, 

Retrofit

Site 1

Cazenovia/

Ballina

Install HPWH 

and distribution 

improvements 

Dec. 1, 2012 

April 3, 2013 

recirculation

pump

April 10, 2013 

HPWH

Group 3, 

Retrofit

Site 2

Syracuse/

Gifford

Install 

condensing 

tank, 

distribution 

improvements

Dec. 15, 2012 May 20, 2013 

Group 2,

Tankless

Site 3

Manlius

Install tankless 

unit Dec. 13, 2012 March 22, 2013 

Group 1,

Baseline

Site 4

Cazenovia/Burton None Dec. 26, 2012 – 

Group 1,

Baseline

Site 5

Syracuse/Hornady None Dec. 14, 2012 – 
6 

Figure 1 schematically shows the location of the instrumentation for a typical water heating 

system. All the monitored points are listed in Table 2. For each system, the cold inlet 

temperature (TC), hot outlet temperature (TH), and water flow (FW) were measured to 

determine delivered energy (QH) from the water heater. The low-mass type-T thermocouples 

(± 1°F) were attached to the outside of the copper pipe using thermally conductive paste. The 

surface-mounted sensors were well insulated to shield them from ambient conditions 

surrounding the pipe. On well-insulated copper pipes we found that the transient response of 

the sensor in detecting the internal fluid temperature was within a few seconds. The transient 

response of the temperature sensor on cross-linked polyethylene (PEX) piping was much 

slower because of the thermal resistance of the pipe wall. The high resolution flow meter 

provided 151 pulse/gal (accuracy is ± 2% of reading at flows under 0.6 gpm, ± 1.5% at 

higher flow rates). The accuracy was confirmed at each site with a measured volume test of 

approximately 1 gal. 

Figure 1. Schematic showing monitored points collected at a typical test site 

exhaust 

gas

TFG

TC

DHW 

Unit

natural 

gas

electric

Trunk

Kitchen

sink dishwasher

Bath 1

sink bath

sink

bath

Bath 2 Utility 

sink

Washing 

machine

TH

WU

SE1

SE2

FG FW

TT1

TT2 TT3

TT4

TF1 TF2

TF3 TF4

TF5

TF6

TF8

TF7

TA1

TA2
7 

Table 2. Data Points Monitored at Typical Site

Total unit power use (WE) was measured for each new electric unit. New units with a 

resistance heating element such as electric tanks or an HPWH also had a status measurement 

to record the runtime of that component (SE1, SE2). Gas use (FG) was measured for the new 

gas units with a temperature-compensated gas meter (0.25 CF per pulse). Flue gas 

temperature (TFG) was measured for all gas-fired units with a type-T thermocouple. For 

conventional gas-fired tanks in Group 1, gas use was not directly measured but the flue gas 

sensor was used to infer unit runtime. Ambient air temperature around the water heater and in 

unconditioned areas with significant hot water piping runs was also measured (TA1, TA2, 

etc.). Relative humidity was measured at Site 1, which has an HPWH. 

Low mass thermocouples were also installed on the outside of the trunk, branch, and fixture 

pipes (i.e., “twigs”) to determine the path of hot water flow during each draw. Where 

practical, we installed a thermocouple on the dedicated line or twig to each point of hot water 

use or fixture (TF1, TF2, etc.). Temperature sensors were installed on trunk or branch lines to 

major areas (kitchen, bath, etc.) to help determine the path of hot water flow (TT1, TT2, 

etc.). In some cases it was not possible to measure the temperature of every location (e.g., 

second-floor showers), but we endeavored to measure enough points to provide meaningful 

results for each fixture. At several sites we installed wireless Campbell Scientific CR206X 

data loggers to record temperature measurements in areas that could not be reached with 

hard-wired sensors. Two CR206X loggers were installed in the two upstairs bathrooms at 

Site 1. At Site 4, CR206X loggers were installed in a remote basement and in an upstairs 

bathroom. Site 5 used a CR206X in the kitchen area. Data from these remote, wireless 

loggers were transferred back to the CR1000 at least every 5 seconds. 

Data 

Point Description Instrumentation EnglishUnits

TC Cold water inlet temperature Type-T TC, 1/16 in. probe (± 1°F) °F

TH Hot water outlet temperature Type-T TC, 1/16 in. probe (± 1°F) °F

FW Hot water flow rate Omega FTB4605 1⁄2 in.

(151 ppg, ± 2% below 0.6 gpm) Gal

TA1 Space temperature near unit Type-T TC, 1/16 in. probe (± 1°F) °F

TA2 Space temperature near piping Type-T TC 1/16 in. probe (± 1°F) °F

TTn Trunk temperature – Location “n” Type-T TC, 1/16 in. probe (± 1°F) °F

TFn Fixture temperature – Location “n” Type-T TC, 1/16 in. probe (± 1°F) °F

TFG Flue gas temperature Type-T TC, 1/16 in. probe (± 1°F) °F

SEn Status, elect element (if applicable) Veris 300 current switch Min

WU Unit electric use (if applicable) Wattnode WNB-3Y-208-P (± 1%) Wh

FG Unit gas use (if applicable) Gas meter (0.25 CF/p) CF
8 

Each site had a Campbell Scientific CR1000 data logger installed to collect averaged or 

totalized data at 15-minute intervals. The data logger was programmed to sample each sensor 

at a 5-second scan rate. In addition, several key data points (FW, TC, TH, TTn and TFn) 

were recorded at 5-second intervals while a draw is occurring. This short time step data 

collection is initiated once any flow occurs (i.e., when one or more pulses are detected) and 

continues for at least five intervals (25 seconds) after the last flow pulse is detected. The 

CR1000 data loggers were connected to the wireless network in each home via a wireless 

bridge. The data loggers were programmed to send data to CDH servers each night. The 15-

minute and short time step data were stored in separate databases.

Appendix B summarizes the specific instrumentation and data loggers used at each site. It 

also includes the site description and a survey that provides the location of each fixture and 

the effective pipe lengths and volume for each section of the distribution system. The new 

systems and equipment installed at the retrofitted sites are also described.
9 

3 Analysis Approach

3.1 Typical Hot Water Draw Events

The data logger at each site was programmed to collect short time step data (i.e., 5-second 

intervals) for total flow rate and temperature during each hot water draw event. Temperature 

data at the water heater, trunk lines and fixtures were also logged for each interval. The result 

is that a small dataset was collected for each hot water draw event (e.g., the period starting 

with flow and ending with 25 seconds of no flow). Following are analyses of three hot water 

events at Site 1.

Figure 2 through Figure 4 show flow events and temperatures corresponding to the master 

bath shower (in this report when the term shower is used, it indicates either a shower or 

bathtub draw), master bath sink, and kitchen sink. For each figure the plot in the upper left 

shows the flow trace during the event (ending with five intervals at zero flow). The red line 

corresponds to the most common flow rate (in gpm) or “mode” during the event. The plot in 

the lower left shows the various temperatures during the event. Blue lines correspond to 

trunk temperatures (TT1, TT2...) while the green lines are the fixture temperatures (TF1, 

TF2,..). Each line is identified by a number. The plot at the upper right shows the temperature 

rise for each sensor compared to the beginning of the event (using the same colors). The red 

line on the upper right and lower left plots is the supply temperature from the unit (TS). The 

black line on these plots corresponds to the cold water inlet (TC). The trunk line with the 

highest temperature rise is indicated by blue text and the fixture temperature with the biggest 

rise is indicated with green text. 

For Figure 2 the first shower of the day lasts for about 6 minutes (84 intervals) and the total 

draw is more than 8 gal. The temperature leaving the tank increases as expected and the inlet 

cold water temperature drops as cold water flows by the sensor. The trunk to the master 

bedroom increases by 40°F as expected. In this case, there is no temperature sensor for the 

shower fixture; only for the bathroom sink. So a trunk temperature rise with no change in 

fixture temperature indicates a shower. However, the sink temperature did see a small rise 

(< 4°F) that could have confounded the fixture prediction. 

Figure 3 below shows a hot water draw event on the master bath sink following the shower 

event. The temperature leaving the tank (TH) and in the trunk to the master bathroom were 

already at 105°F due to the recent shower. The temperature at the fixture increases quickly 

once the hot water reaches that location. The temperature rise compared to the beginning of 

the event was 32°F. Even with the trunk temperature already warm, a temperature rise of 7°F 

was still apparent.
10 

12/02/12 08:00:05 GAL = 8.79

0. 0. 0. 0. 0. 0. 0. 0.

:0 :1 :2 :3 :4 :5 :6 :7

0.0

0.5

1.0

1.5

2.0

Flow Rate (gpm)

DHW Site 1 

0. 0. 0. 0. 0. 0. 0. 0.

:0 :1 :2 :3 :4 :5 :6 :7

-10

0

10

20

30

Temperature Rise (F)

 TH - Hot TC = Cold 

1 2345

6 

7 8

 

2 

3 45

12/02/12 08:00:05 Intervals=84

0. 0. 0. 0. 0. 0. 0. 0.

:0 :1 :2 :3 :4 :5 :6 :7

40

60

80

100

120

140

Temperature (F)

1 23 45 

6 

7 8

1 

2 3 45 

 TF6: Fixture Temp 6 - Master Bath Sink: Rise= 3.8

 TF7: Fixture Temp 7 - Bathroom 2 Sink: Rise= 0.3

 TT1: Trunk Temp - Master Bathroom: Rise= 40.7

 TT2: Trunk Temp - Bathroom 2: Rise= 5.8

 Master Shower

 Useful GAL = 8.03 (TT > 100. )

Figure 2. Hot water draw at master bath shower—December 2, 2012
11 

Figure 3. Hot water draw at master bath sink—December 2, 2012

Figure 4 shows the subsequent first hot water draw of the day in the kitchen. The trunk 

temperature to the kitchen increases by 21°F and the fixture temperature increases by only 

5.5°F, indicating that hot water was heading for—but apparently never reached—the kitchen 

sink. 

12/02/12 08:09:35 GAL = 1.00

0. 0. 0.10.

:9 :10 :11 :12

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Flow Rate (gpm)

DHW Site 1 

0. 0. 0.10.

:9 :10 :11 :12

-10

0

10

20

30

Temperature Rise (F)

 TH - Hot TC = Cold 

1 2345

6 

7 8

1 

2 3 45

12/02/12 08:09:35 Intervals=31

0. 0. 0.10.

:9 :10 :11 :12

40

60

80

100

120

140

Temperature (F)

1 23 45

6 

7 8

1 

2 

3 45 

 TF6: Fixture Temp 6 - Master Bath Sink: Rise= 32.7

 TF3: Fixture Temp 3 - Sink (half bath): Rise= 0.4

 TT1: Trunk Temp - Master Bathroom: Rise= 7.0

 TT2: Trunk Temp - Bathroom 2: Rise= 0.9

 Master Sink

 Useful GAL = 0.75 (TF > 90. )
12 

Figure 4. Hot water draw at kitchen sink—December 2, 2012

3.2 Classifying Draw Events

A classification procedure was developed to classify hot water events and assign them to an 

end use or fixture. The larger text in lower right side in the figures above indicates the end 

use assigned to these particular draws by the procedure. 

Table 3 summarizes how the fixture and trunk temperatures associated with each fixture are 

used to assign hot water draws at Site 1. The temperature rise for any fixture ‘n’ is defined as 

TFnrise = TFnmax – TFn0

Where TFn0 is the temperature for the first interval of the event and TFnmax is the maximum 

value observed during the event. Most fixtures at Site 1 have a temperature associated with 

them except for the upstairs master bathroom shower. In this case a temperature rise on the 

master bath trunk temperature (TT1) with a total draw of more than 1.5 gal causes it to be 

associated with this fixture. Similarly, a temperature rise on the master bath sink must be 

coupled with a total draw of less than 1.5 gal to be associated with that fixture. 

12/02/12 09:05:50 GAL = 0.27

45.50.55. 0. 5. 10.15.20.25.30.35.

:5 :6

0.0

0.2

0.4

0.6

0.8

1.0

Flow Rate (gpm)

DHW Site 1 

45.50.55. 0. 5. 10.15.20.25.30.35.

:5 :6

-10

0

10

20

30

Temperature Rise (F)

 TH - Hot TC = Cold 

1 

2 

1 23 45678

3 

4 5

12/02/12 09:05:50 Intervals=10

45.50.55. 0. 5. 10.15.20.25.30.35.

:5 :6

40

60

80

100

120

140

Temperature (F)

1 2 345 

6 

7 8 

1 

2 3 

4 5 

 TF2: Fixture Temp 2 - Kitchen Sink: Rise= 5.5

 TF3: Fixture Temp 3 - Sink (half bath): Rise= 0.4

 TT3: Trunk Temp 3 - Kitchen Trunk: Rise= 21.6

 TT4: Trunk Temp 4 - Half Bath Trunk: Rise= 0.2

 Kitchen Sink

 Useful GAL = 0.00 (TF > 90. )
13 

Table 3. Logic Table for Fixture and Trunk Temperatures (Site 1) 

Once the draw has been associated with fixture, or “classified,” we used the appropriate end 

use temperature sensor to estimate what portion of the water draw was “useful.” Hot water is 

deemed useful for all intervals during a draw event where 

TF > Tthreshold

If the fixture is associated with a trunk temperature (such as for the master shower in Table 

3), then the intervals deemed as useful have a slightly higher threshold of 

TT > Tthreshold + 10°F 

We used 90°F for Tthreshold at all sites. The selection of this threshold level did not affect the 

classification process. However, the determination of the useful portion of each draw is 

expected to depend on the selected value. Therefore, a sensitivity analysis of threshold value 

is given in Section 4.3. 

We developed similar criteria for Sites 2 through 5. Table 4 through Table 7 summarize the 

criteria that were applied at these sites.

Table 4. Logic Table for Fixture and Trunk Temperatures (Site 2) 

Fixture Logical Test Event Range Check

Dishwasher TF1rise is highest and TF1rise > 2°F –

Kitchen Sink TF2rise is highest and TF2rise > 2°F –

Half Bath Sink TF3rise is highest and TF3rise > 2°F –

Wash Machine TF4rise is highest and TF4rise > 2°F –

Utility Sink TF5rise is highest and TF5rise > 2°F –

Master Sink TF6rise is highest and TF6rise > 2°F < 1.5 gal

Master Shower TT1rise is highest and TT1rise > 4°F > 1.5 gal

Bath 2 Sink TF7rise is highest and TF7rise > 2°F –

Bath 2 Shower TF8rise is highest and TF8rise > 2°F –

Fixture Logical Test Event Range Check

Bath Sink TF1rise is highest and TF1rise > 2°F –

Bath Shower TF2rise is highest and TF2rise > 2°F –

Kitchen Sink TF3rise is highest and TF3rise > 2°F –

Wash Machine TF4rise is highest and TF4rise > 2°F –
14 

Table 5. Logic Table for Fixture and Trunk Temperatures (Site 3) 

Table 6. Logic Table for Fixture and Trunk Temperatures (Site 4) 

Table 7. Logic Table for Fixture and Trunk Temperatures (Site 5) 

Fixture Logical Test Event Range Check

Bath 1 Sink TF1rise is highest and TF1rise > 2°F –

Bath 1 Shower TF2rise is highest and TF2rise > 2°F –

Bath 2 Sink TF3rise is highest and TF3rise > 2°F –

Bath 2 Shower TF4rise is highest and TF4rise > 2°F –

Kitchen Sink TF5rise is highest and TF5rise > 2°F –

Dishwasher TF6rise is highest and TF6rise > 2°F –

Wash Machine TF7rise is highest and TF7rise > 2°F –

Laundry Sink TF8rise is highest and TF8rise > 2°F –

Fixture Logical Test Event Range Check

Master Sink TF1rise is highest and TF1rise > 2°F –

Wash Machine TF2rise is highest and TF2rise > 2°F –

Kitchen Sink TF3rise is highest and TF3rise > 2°F –

Laundry Sink TF4rise is highest and TF4rise > 2°F –

Master Shower TF5rise is highest and TF5rise > 2°F –

Utility Sink TF6rise is highest and TF6rise > 2°F –

Old Bath Sink TF7rise is highest and TF7rise > 2°F –

Old Bath Shower TT1rise is highest and TT1rise > 4°F > 4 gal

Fixture Logical Test Event Range Check

Lower Sink TF1rise is highest and TF1rise > 2°F –

Lower Shower TF2rise is highest and TF2rise > 2°F –

Wash Machine TF3rise is highest and TF3rise > 2°F –

Laundry Sink TF4rise is highest and TF4rise > 2°F –

Upper Sink TF5rise is highest and TF5rise > 2°F –

Upper Shower TF6rise is highest and TF6rise > 2°F –

Kitchen Sink TF7rise is highest and TF7rise > 2°F –

Dishwasher TF8rise is highest and TF8rise > 2°F –
15 

3.3 Errors in Classifying Draw Events

The Results section that follows provides overall statistics on the success of the classification 

process. This subsection looks at some draws that were not properly identified.

Figure 5 shows a draw event in the master bath shower at Site 1 that could not be properly 

identified since the temperature rise on the master bath trunk was lower than the temperature 

rise on the bath 2 trunk. The master bath trunk was already up to temperature before the 

event began, so the rise was small. As is normally observed, the bath 2 trunk is slowly heated 

when there is flow to the master bath. In this case, the first part of the draw (at 0.9 gpm) was 

apparently a draw at the master bath sink. The shower began when the flow jumped to 1.3 

gpm. So these two separate draws were classified as a single draw event. 

Figure 5. Hot water draw that was unclassified, Site 1, December 5, 2012

Similarly, the draw event shown in Figure 6 (also Site 1) was also two draws combined but it 

was misclassified as a bath 2 sink draw, but only the second portion corresponds to that 

fixture. The first part of the draw was due to the master bath shower. In this case the useful 

hot water draw was more than 3.8 gal while the total draw was more than 13 gal. The 

difference between the useful and the total water draw provides an indication, in this case,

that there could be a classification error.

12/05/12 14:25:45 GAL = 13.86

:38

14:

0.0

0.5

1.0

1.5

2.0

Flow Rate (gpm)

DHW Site 1 

:38

14:

-10

0

10

20

30

Temperature Rise (F)

 TH - Hot TC = Cold 

1 2345

6 

1 7 8

2 

3 45

12/05/12 14:25:45 Intervals=142

:38

14:

40

60

80

100

120

140

Temperature (F)

1 2 3 4 5

6 

7 8

1 

2 

3 4 5 

 TF6: Fixture Temp 6 - Master Bath Sink: Rise= 26.0

 TF8: Fixture Temp 8 - Bathroom 2 Shower: Rise= 0.5

 TT2: Trunk Temp - Bathroom 2: Rise= 4.0

 TT1: Trunk Temp - Master Bathroom: Rise= 1.1

 
16 

Figure 6. Hot water draw that was misclassified, Site 1, December 15, 2012

At Site 4 there are two hot water systems in the house (see Appendix B): (1) an old 

conventional gas-fired tank that serves the old bathroom; and (2) a new tankless water heater 

that serves an addition that includes most other fixtures in the home. Figure 7 shows that the 

draw for the old bath shower (on the old water heater, blue data) happens at the same time as 

the kitchen sink/dishwasher (on the tankless water heater, black data). 

12/15/12 23:52:00 GAL = 15.56

:0 :1 :2 :3 :4

23: 0:

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Flow Rate (gpm)

DHW Site 1 

:0 :1 :2 :3 :4

23: 0:

-10

0

10

20

30

Temperature Rise (F)

 TH - Hot TC = Cold 

1 23456 8 

 

 

3 45

12/15/12 23:52:00 Intervals=140

:0 :1 :2 :3 :4

23: 0:

40

60

80

100

120

140

Temperature (F)

1 234 5 

6 

7 

8 

1 2

3 4 5 

 TF7: Fixture Temp 7 - Bathroom 2 Sink: Rise= 49.4

 TF6: Fixture Temp 6 - Master Bath Sink: Rise= 2.1

 TT2: Trunk Temp - Bathroom 2: Rise= 50.2

 TT1: Trunk Temp - Master Bathroom: Rise= 48.8

 Bath2 Sink

 Useful GAL = 3.83 (TF > 90. )
17 

Figure 7. Hot water draw that was misclassified, Site 4, December 27, 2012

12/27/12 22:26:30 GAL = 35.00

:43

22:

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Flow Rate (gpm)

DHW Site 4 

:43

22:

-10

0

10

20

30

Temperature Rise (F)

 TH - Hot TC = Cold 

1 2456 7 

 

12/27/12 22:26:30 Intervals=190

:43

22:

40

60

80

100

120

140

Temperature (F)

1 

2 

3 

4 5 6 7 

1 

 TF3: Fixture Temp 3 - Kitchen Sink: Rise= 38.4

 TT7: Trunk Temp 7 - Old Bathroom: Rise= 41.9

 Old Bath Shower

 Useful GAL = 0.71 (TT > 100. )
18 

4 Pre-Retrofit or Baseline Results

4.1 Classifying Draw Events at Each Site

The classification procedures described in the previous section were applied to each site for

the data collected in the pre-retrofit periods for Sites 1, 2, and 3 and for the entire period for 

Sites 4 and 5. The results of that process are shown for each site in the following tables and 

figures. The figures show the total hot water use verses the draw rate (or mode) for each 

event. This type of graph was used by Magnusson (2009) to qualitatively illustrate the 

characteristics of various draw types.

The results for Site 1 are shown in Table 8, Figure 8, and Figure 9. This home has two adults 

and two college-age students who returned for the college breaks (who mostly used bathroom 

2). Fewer than half of the 8,534 events in the 123-day period could be assigned. However, 

these classified (or assigned) events accounted for 94% of the total water use. Numerous 

small events could not be assigned (these are shown as black “+” on the plots). The average 

unclassified event was less than 0.1 gal. Of the unclassified events, only 18 were more than 1 

gal in the 123-day period. One of the biggest unclassified events is shown in the previous 

section in Figure 5. Overall, about 82% of the total classified water use was deemed to be

useful, based on the 90°F threshold. As expected, the sinks result in the largest amount of hot 

water waste on a percentage basis.

Table 8. Summary of Results for Site 1, December 1, 2012 to April 2, 2013 (123 Days)

Site 1 Events 

per Day 

Total Hot 

Water Use 

(gpd)

Useful Hot 

Water

(gpd)

Wasted 

Hot Water 

(gpd)

Useful %

Dishwasher 1.5 2.7 2.4 0.3 90%

Kitchen Sink 17.0 9.1 5.7 3.3 63%

Half Bath Sink 2.1 0.7 0.1 0.5 21%

Washing Mach 0.7 9.1 8.3 0.8 91%

Utility Sink 0.3 0.9 0.5 0.4 53%

Master Sink 6.8 2.2 0.6 1.5 28%

Master Shower 1.5 17.8 17.0 0.8 95%

Bath 2 Sink 1.7 1.2 0.6 0.6 49%

Bath 2 Shower 0.7 8.4 7.7 0.8 91%

Unaccounted 36.8 3.4 – 3.4 0%

All Events 69.4 55.4 42.9 12.5 77%

Classified 33 52.0 42.9 9.1 82%

% Classified 47% 94% 100% 73%

No. of Events 8,534
19 

Figure 8. Summary of classified draw events, Site 1, December 1 to April 2: 0–40 gal

DHW Site 1 12/01/12 07:45:00 to 04/02/13 23:00:55 (Total Events = 8534 )

0 20 40

HW Use (Gal)

0

1

2

3

4

5

Draw Rate (gpm)

Dishwasher 185

Kitchen Sink 2095

Halfbath Sink 260

Washing Mach 88

Utility Sink 42

Master Sink 842

Master Shower 190

Bath2 Sink 212

Bath2 Shower 91

Classified Events = 4005

DHW Site 1 12/01/12 07:45:00 to 04/02/13 23:00:55 (Total Events = 8534 )

0 1 2 3 4 5

HW Use (Gal)

0

1

2

3

4

5

Draw Rate (gpm)

Dishwasher 185

Kitchen Sink 2095

Halfbath Sink 260

Washing Mach 88

Utility Sink 42

Master Sink 842

Master Shower 190

Bath2 Sink 212

Bath2 Shower 91

Figure 9. Summary of classified draw events, Site 1, December 1 to April 2: 0–5 gal
20 

The results for Site 2 are shown in Table 9, Figure 10, and Figure 11. This home has two 

occupants. Fewer than half of the 4,648 events in the 157-day period could be assigned. 

However, these classified events accounted for 98% of the total water use. Numerous small 

events could not be assigned. The average unclassified event was approximately 0.05 gal.

Only six of the unclassified events were more than 1 gal. Overall 87% of the total classified 

water use was deemed to be useful. One very large draw exceeding 164 gal and lasting more 

than 1 hour occurred when the occupants apparently left the bathtub running in December. 

Some of the bath shower draws were misclassified as bath sink draws because the 

temperature rise was slightly higher at the sink fixture (or because simultaneous draws 

occurred). 

Table 9. Summary of Results for Site 2, December 14, 2012 to May 19, 2013 (157 Days) 

Site 2 Events 

per Day 

Total Hot 

Water Use 

(gpd)

Useful Hot 

Water 

(gpd)

Wasted 

Hot Water 

(gpd)

Useful 

% 

Bath Sink 4.0 4.8 4.7 0.2 96%

Bath Shower 3.2 41.9 37.1 4.8 89%

Kitchen Sink 2.3 3.0 1.8 1.1 62%

Washing Mach 2.0 1.3 0.7 0.6 56%

Unaccounted 18.2 1.0 - 1.0 0%

All Events 29.6 52.0 44.3 7.7 85%

Classified 11.5 51.0 44.3 6.7 87%

% Classified 39% 98% 100% 86%

No. of Events 4,648

DHW Site 2 12/14/12 10:05:45 to 05/19/13 20:00:35 (Total Events = 4648 )

0 20 40

HW Use (Gal)

0

1

2

3

4

5

Draw Rate (gpm)

Bath Sink 630

Bath Shower 502

Kitchen Sink 353

Washing Mach 315

Classified Events = 1800

misclassified as 

“Bath Sink” 

Figure 10. Summary of classified draw events, Site 2, December 14 to May 19: 0–40 gal
21 

Figure 11. Summary of classified draw events, Site 2, December 14 to May 19: 0–5 gal

The results for Site 3 are shown in Table 10, Figure 12, and Figure 13. This home has two 

adult occupants. About half of the 2,909 events in the 98-day period could be assigned. 

However, these classified events accounted for 94% of the total hot water use. Numerous 

small events could not be assigned. The average unclassified event was about 0.1 gal. Only 

17 of the unclassified events were more than 1 gal. Overall, 90% of the total classified water 

use was deemed to be useful. 

Table 10. Summary of Results for Site 3, December 13, 2012 to March 22, 2013 (98 Days)

Site 3 Events 

per Day 

Total Hot 

Water Use 

(gpd)

Useful Hot 

Water 

(gpd)

Wasted 

Hot Water 

(gpd)

Useful 

% 

Bath 1 Sink 0.2 0.4 0.3 0.1 78%

Bath 1 Shower 1.4 18.2 17.1 1.0 94%

Bath 2 Sink 5.8 1.7 1.2 0.5 69%

Bath 2 Shower 0.1 1.7 1.7 0.0 98%

Kitchen Sink 5.8 4.8 3.8 1.0 80%

Dishwasher 1.7 2.0 1.7 0.3 86%

Washing Machine 0.7 3.4 3.2 0.2 94%

Laundry Sink 0.0 0.1 0.1 0.0 93%

Unaccounted 14.1 2.0 – 2.0 0%

All Events 29.6 34.3 29.2 5.1 85%

Classified 15.6 32.3 29.2 3.1 90%

% Classified 53% 94% 100% 60%

No. of Events 2,909

DHW Site 2 12/14/12 10:05:45 to 05/19/13 20:00:35 (Total Events = 4648 )

0 1 2 3 4 5

HW Use (Gal)

0

1

2

3

4

5

Draw Rate (gpm)

Bath Sink 630

Bath Shower 502

Kitchen Sink 353

Washing Mach 315
22 

Figure 12. Summary of classified draw events, Site 3, December 13 to March 22: 0–40 gal

DHW Site 3 12/13/12 19:21:35 to 03/21/13 19:59:00 (Total Events = 2909 )

0 20 40

HW Use (Gal)

0

1

2

3

4

5

Draw Rate (gpm)

Bath1 Sink 20

Bath1 Shower 134

Bath2 Sink 566

Bath2 Shower 8

Kitchen Sink 569

Dishwasher 163

Wash Machine 65

Laundry Sink 3

Classified Events = 1528

DHW Site 3 12/13/12 19:21:35 to 03/21/13 19:59:00 (Total Events = 2909 )

0 1 2 3 4 5

HW Use (Gal)

0

1

2

3

4

5

Draw Rate (gpm)

Bath1 Sink 20

Bath1 Shower 134

Bath2 Sink 566

Bath2 Shower 8

Kitchen Sink 569

Dishwasher 163

Wash Machine 65

Laundry Sink 3

Figure 13. Summary of classified draw events, Site 3, December 13 to March 22: 0–5 gal
23 

The results for Site 4 are shown in Table 11, Figure 14, and Figure 15. This home has two 

adults and three high school or college-age children. Only 17% of the 36,592 events in the 

202-day period could be assigned. However, these classified events accounted for 88% of the 

total water use. Numerous small events could not be assigned. The average unclassified event 

was less than 0.1 gal. More than 200 of the unclassified events exceeded 1 gal. Overall, about 

75% of the total classified water use was deemed to be useful. The placement of sensors on 

the PEX tubing may have provided a slower response than the sensors installed on copper 

piping at the other sites, resulting in a delay in sensing the time when the water temperature 

reached the assumed threshold of 90°F. 

Table 11. Summary of Results for Site 4, December 10, 2012 to June 30, 2013 (202 Days)

Site 4 Events 

per Day 

Total Hot 

Water Use 

(gpd)

Useful Hot 

Water 

(gpd)

Wasted 

Hot Water 

(gpd)

Useful 

% 

Master Sink 6.8 6.4 2.5 3.8 40%

Washing Machine 1.1 1.8 0.2 1.5 14%

Kitchen Sink 15.8 19.4 12.5 7.0 64%

Laundry Sink - - - -

Master Shower 2.7 39.4 34.9 4.5 89%

Utility Sink 0.0 0.1 - 0.1 0%

Old Bath Sink 2.9 3.5 1.8 1.7 51%

Old Bath Shower 1.4 31.8 25.2 6.6 79%

Unaccounted 150.3 13.3 - 13.3 0%

All Events 180.9 115.8 77.2 38.6 67%

Classified 30.6 102.4 77.2 25.2 75%

% Classified 17% 88% 100% 65%

No. of Events 36,592

The breakdown of hot water use over 7 months for Site 4 is shown in Figure 16. The monthly 

variation the “usefulness” of draws by end use is shown in Figure 17 for the same period. 

The hot water use did vary significantly across the period, with the highest value in March 

2013 (when cold water inlet temperatures were lowest). The useful portion of the draws did 

not show as much variation, with the exception of the washing machine, which did show 

random monthly variations in “usefulness.” 
24 

Figure 14. Summary of classified draw events, Site 4, December 26–30, 2012: 0–40 gal

DHW Site 4 12/10/12 14:30:45 to 06/30/13 19:41:45 (Total Events = 36592 )

0 20 40

HW Use (Gal)

0

1

2

3

4

5

Draw Rate (gpm)

Master Sink 1370

Wash Machine 219

Kitchen Sink 3203

Laundry Sink 0

Master Shower 538

Utility Sink 2

old Bath Sink 578

Old Bath Shower 283

Classified Events = 6193

DHW Site 4 12/10/12 14:30:45 to 06/30/13 19:41:45 (Total Events = 36592 )

0 1 2 3 4 5

HW Use (Gal)

0

1

2

3

4

5

Draw Rate (gpm)

Master Sink 1370

Wash Machine 219

Kitchen Sink 3203

Laundry Sink 0

Master Shower 538

Utility Sink 2

old Bath Sink 578

Old Bath Shower 283

Figure 15. Summary of classified draw events, Site 4, December 26–30, 2012: 0–5 gal
25 

 ‘

Figure 16. Monthly breakdown of hot water use (Site 4) 

Figure 17. Monthly variation of “usefulness” by end use (Site 4) 

The results for Site 5 are shown in Table 12, Figure 18, and Figure 19. This home has two 

adults. Slightly more than a half of the 5,191 events in the 198-day period could be assigned. 

However, these classified events accounted for 98% of the total water use. Numerous small 

events could not be assigned. The average unclassified event was less than 0.1 gal. Only

three of the unclassified events were more than 1 gal. Overall, 91% of the total classified 

water use was deemed to be useful. 

0

20

40

60

80

100

120

140

Dec-12 Jan-13 Feb-13 Mar-13 Apr-13 May-13 Jun-13

HW Use (gal/day)

Wash Mach/Utility

Kitchen

Bath Showers

Bath Sinks

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Dec-12 Jan-13 Feb-13 Mar-13 Apr-13 May-13 Jun-13

Bath Sinks

Bath Showers

Kitchen

Wash Mach/Utility
26 

Table 12. Summary of Results for Site 5, December 14, 2012 to June 30, 2013 (198 Days)

Site 5 Events 

per Day 

Total Hot 

Water Use 

(gpd)

Useful Hot 

Water 

(gpd)

Wasted 

Hot Water 

(gpd)

Useful 

% 

Lower Sink 1.0 1.3 1.0 0.3 79%

Lower Shower 0.4 4.0 3.7 0.4 91%

Washing Machine 0.5 3.5 3.3 0.1 97%

Laundry Sink 0.1 0.4 0.3 0.0 94%

Upper Sink 3.0 7.5 6.6 1.0 87%

Upper Shower 1.9 20.9 19.7 1.2 94%

Kitchen Sink 4.2 2.1 1.4 0.7 66%

Dishwasher 3.9 5.3 4.9 0.4 93%

Unaccounted 11.2 0.8 - 0.8 0%

All Events 26.2 45.7 41.0 4.7 90%

Classified 15.0 44.9 41.0 4.0 91%

% Classified 57% 98% 100% 84% –

No. of Events 5,191

The breakdown of hot water use over 7 months for Site 5 is shown in Figure 20. The monthly 

variation the “usefulness” of draws by end use is shown in Figure 21 for the same period. 

Neither hot water use nor the useful portion of the draws showed a significant amount of 

variation. 

DHW Site 5 12/14/12 12:56:25 to 06/30/13 20:15:40 (Total Events = 5191 )

0 20 40

HW Use (Gal)

0

1

2

3

4

5

Draw Rate (gpm)

Lower Sink 201

Lower Shower 82

Wash Machine 100

Laundry Sink 15

Upper Sink 594

Upper Shower 380

Kitchen Sink 834

DishWasher 768

Classified Events = 2974

Figure 18. Summary of classified draw events, Site 5, December 14 to June 30: 0–40 gal
27 

Figure 19. Summary of classified draw events, Site 5, December 14 to June 30: 0–5 gal 

DHW Site 5 12/14/12 12:56:25 to 06/30/13 20:15:40 (Total Events = 5191 )

0 1 2 3 4 5

HW Use (Gal)

0

1

2

3

4

5

Draw Rate (gpm)

Lower Sink 201

Lower Shower 82

Wash Machine 100

Laundry Sink 15

Upper Sink 594

Upper Shower 380

Kitchen Sink 834

DishWasher 768

0

5

10

15

20

25

30

35

40

45

50

Dec-12 Jan-13 Feb-13 Mar-13 Apr-13 May-13 Jun-13

HW Use (gal/day)

Wash Mach/Utility

Kitchen

Bath Showers

Bath Sinks

Figure 20. Monthly breakdown of hot water use (Site 5)
28 

Figure 21. Monthly variation of “usefulness” by end use (Site 5) 

4.2 Summary of Cross-Site Performance

Figure 22 and Figure 23 compare the breakdown of hot water use in the five homes. As 

expected, showers (and baths) account for the largest portion of hot water use in all the 

houses. The kitchen sink and dishwater are the next largest end uses in three of the five 

houses. 

Total daily hot water use ranged between 40 and 60 gal at three of the houses. At Site 2 the 

usage was a little more than 30 gpd. At Site 4, the two adults and three teenage children used 

more than 100 gpd. 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Dec-12 Jan-13 Feb-13 Mar-13 Apr-13 May-13 Jun-13

Portion of Draw that is "Useful"

Bath Sinks

Bath Showers

Kitchen

Wash Mach/Utility
29 

Figure 22. Breakdown of hot water use by end use

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Site 1 Site 2 Site 3 Site 4 Site 5

Portion of Water Use

Wash Mach/Utility

Kitchen

Bath Showers

Bath Sinks

-

20 

40 

60 

80 

100 

120 

Site 1 Site 2 Site 3 Site 4 Site 5

HW Use (gal/day)

Wash Mach/Utility

Kitchen

Bath Showers

Bath Sinks

Figure 23. Breakdown of daily hot water use by end use
30 

All the classified draws were also evaluated to determine the portion of the water use that 

was useful. Water at the fixture above a threshold temperature of 90°F was deemed to be 

useful. Figure 24 shows the percentage of draws associated with each major end use category 

that were deemed useful. Showers (and tubs) typically have highest percentage of useful hot 

water, with three sites exceeding 90% and two sites exceeding 80%. Washing machine draws 

also have a high useful percentage. Bathroom sinks have a lower useful draw percentage, as 

would be expected. 

Some notable exceptions to the overall trends included: 

• Site 2 has a high useful percentage for the bathroom sink since it is very close to the 

water heater.

• The Site 4 washing machine had a lower useful percentage. 

Figure 24. Portion of hot water deemed as useful from each end use

Table 13 summarizes the statistics for the portion of hot water use events that were able to be 

classified and assigned to a fixture at the five sites. Generally, about half of the events (42%) 

could be assigned, though 95% of the hot water use could be accounted for. The unclassified 

(or unassigned) draws were typically on the order of 0.1 gal. Only a small portion of 

unclassified draws were more than 1 gal.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Site 1 Site 2 Site 3 Site 4 Site 5

Portion of Draw that is "Useful"

Bath Sinks

Bath Showers

Kitchen

Wash Mach/Utility
31 

Table 13. Summary of Classification Statistics for Five Sites

Site 1 Site 2 Site 3 Site 4 Site 5

Classified Events 47% 39% 53% 17% 57%

Classified Use 94% 98% 94% 88% 98%

4.3 Assessing the Impact of Threshold Level

The threshold level of 90°F for determining the useful portion of each draw was a somewhat 

arbitrary value. While this definition of might be appropriate for sinks, some argue that a 

higher value (say 105°F) might be more appropriate for showers and other end uses. 

The plots and tables below assess the impact of using a different threshold of 80°F and 100°F 

at each site. Table 14 and Figure 25 show the results for Site 1. Generally the sinks and 

dishwasher show the most sensitivity to threshold level. Table 15 and Figure 26 show the 

results for Site 2. In this case the kitchen sink and washing machine are most sensitive to the 

threshold level. Table 16 and Figure 27 show the results for Site 3. Again bathroom sinks, the 

kitchen sink, and the dishwasher are the most sensitive. Table 17 and Figure 28 show the 

results for Site 4. The slow response of the surface-mounted sensor on PEX piping at this site 

means that the threshold has a big impact on the determination of “usefulness.” The fixtures 

in the old bathroom seem to rarely reach 100°F since that water heater has lower setting.

Finally the results for Site 5 are shown in Table 18 and Figure 29. At this site the kitchen sink 

showed the most sensitivity to threshold level.

Table 14. Impact of Threshold Temperature on Determining “Usefulness” (Site 1) 

Useful Portion Threshold Temperature

80°F 90°F 100°F

Dishwasher 98% 90% 75%

Kitchen Sink 74% 63% 48%

Half Bath Sink 31% 21% 16%

Washing Machine 93% 91% 89%

Utility Sink 57% 53% 48%

Master Sink 50% 28% 13%

Master Shower 97% 95% 78%

Bath 2 Sink 67% 49% 39%

Bath 2 Shower 93% 91% 89%

88% 82% 71%
32 

Figure 25. Impact of threshold temperature on “usefulness” at each fixture (Site 1) 

Table 15. Impact of Threshold Temperature on Determining “Usefulness” (Site 2) 

Useful Portion Threshold Temperature

80°F 90°F 100°F

Bath Sink 98% 96% 88%

Bath Shower 90% 89% 87%

Kitchen Sink 71% 62% 48%

Washing Machine 66% 56% 40%

89% 87% 84%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Portion of Draw that is "Useful"

80F

90F

100F
33 

Figure 26. Impact of threshold temperature on “usefulness” at each fixture (Site 2) 

Table 16. Impact of Threshold Temperature on Determining “Usefulness” (Site 3) 

Useful Portion Threshold Temperature

80°F 90°F 100°F

Bath 1 Sink 82% 78% 59%

Bath 1 Shower 96% 94% 89%

Bath 2 Sink 78% 69% 52%

Bath 2 Shower 99% 98% 97%

Kitchen Sink 84% 80% 72%

Dishwasher 97% 86% 67%

Washing Machine 96% 94% 93%

Laundry Sink 96% 93% 91%

93% 90% 83%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Bath Sink Bath Shower Kitchen Sink Washing Mach

Portion of Draw that is "USeful"

80F

90F

100F
34 

Figure 27. Impact of threshold temperature on “usefulness” at each fixture (Site 3) 

Table 17. Impact of Threshold Temperature on Determining “Usefulness” (Site 4) 

Useful Portion Threshold Temperature

80°F 90°F 100°F

Master Sink 57% 40% 21%

Washing Machine 38% 14% 6%

Kitchen Sink 80% 64% 39% 

Laundry Sink – – –

Master Shower 93% 89% 82%

Utility Sink 0% 0% 0%

Old Bath Sink 62% 51% 27%

Old Bath Shower 86% 79% 31%

84% 75% 51%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Portion of Draw that is "Useful"

80F

90F

100F
35 

Figure 28. Impact of threshold temperature on “usefulness” at each fixture (Site 4) 

Table 18. Impact of Threshold Temperature on Determining “Usefulness” (Site 5) 

Useful Portion Threshold Temperature

80°F 90°F 100°F

Lower Sink 81% 79% 75%

Lower Shower 93% 91% 89%

Washing Machine 98% 97% 95% 

Laundry Sink 94% 94% 94%

Upper Sink 90% 87% 85%

Upper Shower 96% 94% 90%

Kitchen Sink 77% 66% 54%

Dishwasher 96% 93% 88%

94% 91% 87%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Portion of Draw that is "Useful"

80F

90F

100F
36 

Figure 29. Impact of threshold temperature on “usefulness” at each fixture (Site 5) 

4.4 Propagation of Measurement Errors to the Determination of “Usefulness” 

The sensitivity analysis also provided the means to propagate the measurement uncertainty 

associated with the temperature sensors and flow meters and determine its impact on the 

prediction of usefulness. 

Table 19 uses the results of the sensitivity analysis to estimate the uncertainty in the 

determination of “usefulness” for each site. The measurement errors for flow and 

temperature are propagated using the estimated sensor errors. The probable error in the 

determination of “usefulness” is estimated to be ± 2% for Sites 1, 2, 3, and 5 with copper 

piping and ± 5 % at Site 4 where PEX piping was used. 

Table 19. Propagation of Measurement Errors to Error in Determination of “Usefulness” 

Estimated Error 

in Threshold 

Temperature 

(± °F)a

Slope: 

Usefulness 

% per °F

(%/ °F)b

Error From 

Temperature 

(± %)c

Error 

From 

Flow

(± %)d

Combined 

Probable 

Error

(± %)e

Site 1 2 0.6 1.2 1.6 2.0

Site 2 2 0.2 0.4 1.7 1.8

Site 3 2 0.3 0.6 1.8 1.9

Site 4 5 0.9 4.5 1.5 4.7

Site 5 2 0.3 0.6 1.8 1.9 a Estimated error in determining threshold temperature includes a static error of ± 1°F as well as an additional 

estimated transient response error of ± 1°F for copper pipes and ± 4°F for PEX piping.

b Slope is taken from difference between 80°F and 90°F thresholds in Tables 25 to 29 above. c Temperature error is product of (a) and (b) 

d Flow error is ± 2% of average usefulness e Probable error is square root of sum of squares of (c) and (d)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Portion of Draw that is "Useful"

80F

90F

100F
37 

5 Impact of Retrofits

5.1 Impact of Tankless Retrofit at Site 3 (Group 2)

At Site 3 a tankless water heater (Rinnai RL75i) was installed to replace the conventional 

gas-fired tank on March 22, 2013. The system cost $2,420 to install (see Appendix B). The 

impact of this change on this household with two people is shown in the plots below. Figure 

30 shows data for the pre-retrofit period with the conventional gas-fired tank as black, while 

data with the tankless unit (after March 22) are shown as red. Total water use changed only 

slightly; however, the number of hot water draws was reduced by more than 50% with the 

tankless unit. The minimum activation flow threshold of 0.4 gpm for the tankless unit (as 

well as the startup delay) apparently caused the occupants to change their hot water use 

behavior (i.e., they learned to stop making small draws when they wanted to get hot water). 

Figure 30. Comparing pre- and post-retrofit periods (Site 3) 

Figure 31 and Table 20 shows how the useful percentage of hot water use for each month 

changed across the monitoring period. The overall percentage of useful hot water use 

decreased from 90%–91% with the conventional tank to 84%–86% with the tankless unit. 

This reduction in useful delivered hot water is mostly due to the startup delay of the tankless 

unit (i.e., a time delay for burner activation) which results in less hot water being delivered to 

Site 3 (excluding vacations)

31 7 14 21 28 4 11 18 25 4 11 18 25 1 8 15 22 29 6 13 20 27 3 10 17 24 1

January February March April May June

0

20

40

60

80

100

120

Water Use (gal/day)

AVG = 34.5 AVG = 32.8

31 7 14 21 28 4 11 18 25 4 11 18 25 1 8 15 22 29 6 13 20 27 3 10 17 24 1

January February March April May June

0

50

100

150

Draw Events (no/day)

AVG = 52.3 AVG = 19.7

Tankless Water Heater

(post)

Gas-Fired Tank (pre)

Gas-Fired Tank (pre) Tankless Water Heater (post)
38 

the faucet. The largest drops were associated with the kitchen, bath sinks, and laundry end 

uses. The impact of the retrofit on total water use is summarized in Table 21. The sinks 

showed the expected reduction in the number of draw events. Other changes were related to 

known differences in water use between the pre- and post-retrofit periods, such as guests in 

the “bath 2 shower” in the pre-retrofit period. The homeowners also purchased a new energyefficient washing machine on May 2, 2013. This had a significant impact on the washing 

machine water use in the post-retrofit period. 

Figure 31. Plot showing variation of useful water draw percentage across period (Site 3) 

Table 20. Variation of Useful Water Draw Percentage Across Period (Site 3) 

Pre-Retrofit Post-Retrofit

Dec. Total 

2012

Jan. 

2013

Feb. 

2013

Mar. 

2013

Apr. 

2013

May

2013

June 

2013

Bath Sinks 75% 62% 71% 64% 43% 45% 61% 62%

Bath Showers 95% 95% 94% 93% 92% 92% 92% 93%

Kitchen 88% 78% 87% 74% 68% 72% 77% 77%

Washing Machine/Utility 96% 97% 95% 88% 65% 12% 31% 83%

Overall 91% 90% 91% 87% 84% 84% 86% 87%

0%

20%

40%

60%

80%

100%

120%

Portion of Draw that is "Useful"

Bath Sinks

Bath Showers

Kitchen

Wash Mach/Utility

Overall

Pre-Retrofit Post-Retrofit
39 

Table 21. Impact of Retrofit on Events and Hot Water Use 

(Pre-Retrofit = Tank; Post-Retrofit = Tankless) 

Events per Day Total Hot Water Use 

(gpd)

Portion of 

Water Use

PreRetrofitPostRetrofit Notes Portion of 

Water Use

PreRetrofitPostRetrofit Notes

Bath 1 Sink 1% 0.2 0.6 2% 0.4 0.6

Bath 1 Shower 56% 1.4 1.2 70% 18.2 20.9

Bath 2 Sink 5% 5.8 1.4 Fewer small 

events 2% 1.7 0.6 

Bath 2 Shower 5% 0.1 0.0 1% 1.7 0.2 Fewer guests

Kitchen Sink 15% 5.8 4.7 Fewer small

events 15% 4.8 4.5 

Dishwasher 6% 1.7 0.8 5% 2.0 1.5

Washing Machine 11% 0.7 0.6 5% 3.4 1.3 New washing 

machine

Laundry Sink 0% 0.0 0.0 0% 0.1 0.1

Unclassified – 14.1 6.5 Fewer small 

events – 2.0 1.5 

Total – 29.6 15.8 34.3 31.2
40 

The plots below compare typical draw events for three different scenarios before and after 

the water heater and washing machine were replaced:

• Original water heater and original washing machine (Figure 32) 

• New tankless water heater and original washing machine (Figure 33) 

• New tankless water heater and new energy efficient washing machine (Figure 34). 

Table 22 summarizes the performance under these three scenarios. 

Figure 32 shows the expected performance with the conventional water heater and the 

original washing machine (see Section 1.9 for a full description of these plots). The washing 

machine had a draw exceeding 4 gal and most of the draw (3.81 gal) was deemed useful (i.e., 

hotter than 90°F). 

Figure 33 shows what changed when the tankless water heater was installed. The water draw 

was 1–2 gpm yet the tankless burner apparently cycled on and off even though the flow rate 

was well above the 0.28 gpm cutout flow. It is interesting to note that the washing machine’s 

control valve modulated the hot water flow in an attempt to maintain a desired water 

temperature. The period of the oscillations was about 90 seconds. Overall, percentage of 

useful hot water dropped by a nearly factor of two (to 49%). 

Figure 34 shows the energy-efficient washing machine with the tankless water heater. The 

new washing machine attempts to make several small hot water draws that apparently do not 

last long enough to result in significant burner operation; therefore, no hot water is delivered 

to the appliance. The tankless burner fires only briefly after the second draw and as a result 

delivers no water hotter than 90°F to the appliance during the total 1.2-gal draw event.

Table 22. Comparing Water Draws for Different Water Heaters and Washing Machines

Water 

Heater

Washing 

Machine

Total Draw 

(gal)

Useful Draw 

(gal)

Useful 

Percentage

Old (Tank) Old 4.05 3.81 94%

Tankless High Efficiency 5.22 2.58 49%

Tankless High Efficiency 1.24 0 0%
41 

Figure 32. Typical water draw—conventional tank and old washing machine

03/02/13 14:23:25 GAL = 4.05

0. 0. 0. 0. 30.

:23 :24 :25 :26 :27

0.0

0.5

1.0

1.5

2.0

2.5

Flow Rate (gpm)

DHW Site 3 

Time Since Last Draw 5.7 minutes

0. 0. 0. 0. 30.

:23 :24 :25 :26 :27

-10

0

10

20

30

Temperature Rise (F)

 TH = Hot TC = Cold 

1 21 23457

3 

03/02/13 14:23:25 Intervals=47

0. 0. 0. 0. 30.

:23 :24 :25 :26 :27

40

60

80

100

120

140

Temperature (F)

1 

2 3 4 5 

6 

7 

1 

2 

3 

 TF7: Fixture Temp 7 - Washing Machine: Rise= 60.9

 TF8: Fixture Temp 8 - Laundry Sink: Rise= 0.3

 TT4: Trunk Temp - Laundry: Rise= 26.3

 TT3: Trunk Temp - Kitchen: Rise= 0.1

 Wash Machine

 Useful GAL = 3.81 (TF > 90. )

04/21/13 09:21:50 GAL = 5.22

30. 0. 30. 0. 30. 0. 30. 0. 30. 0.

:21:22 :23 :24 :25 :26

0.0

0.5

1.0

1.5

2.0

2.5

Flow Rate (gpm)

DHW Site 3 

Time Since Last Draw 22.8 minutes

30. 0. 30. 0. 30. 0. 30. 0. 30. 0.

:21:22 :23 :24 :25 :26

-10

0

10

20

30

Temperature Rise (F)

 TH = Hot TC = Cold 

1 21 23457

 

04/21/13 09:21:50 Intervals=50

30. 0. 30. 0. 30. 0. 30. 0. 30. 0.

:21:22 :23 :24 :25 :26

40

60

80

100

120

140

Temperature (F)

1 2 3

4 5 

6 

7 1 

2 

3 

 TF7: Fixture Temp 7 - Washing Machine: Rise= 56.3

 TF4: Fixture Temp 4 - Bathroom 2 Shower: Rise= 0.1

 TT4: Trunk Temp - Laundry: Rise= 69.7

 TT1: Trunk Temp - Bathroom 1: Rise= 0.2

 Wash Machine

 Useful GAL = 2.58 (TF > 90. )

Figure 33. Typical water draw—tankless and old washing machine
42 

Figure 34. Typical water draw—tankless and new efficient washing machine

The performance of the two water heaters during a typical kitchen draw are compared in 

Figure 35 and Figure 36. The overall impacts are summarized in Table 23. With the 

conventional water heater tank, hot water is provided immediately and the delay in hot water 

reaching the fixture is the primary reason that the useful percentage is 68%. With the tankless 

water heater unit it takes about 40 seconds for the water exiting the unit to reach full 

temperature. Then it takes another few seconds for the hot water at the sink faucet to reach 

90°F. The net effect is that the portion of the hot water draw deemed useful is much lower 

(31%), even though the draw is slightly larger. 

Table 23. Comparing Kitchen Water Draws With Different Water Heaters 

05/13/13 16:09:10 GAL = 1.24

0.15.30.45. 0.15.30.45.0.15.30.45. 0.15.

:9 :10 :11 :12

0

2

4

Flow Rate (gpm)

DHW Site 3 

Time Since Last Draw 41.2 minutes

0.15.30.45. 0.15.30.45.0.15.30.45. 0.15.

:9 :10 :11 :12

-10

0

10

20

30

Temperature Rise (F)

 TH = Hot TC = Cold 

1 2 345

6 

1 27 

3 

05/13/13 16:09:10 Intervals=36

0.15.30.45. 0.15.30.45.0.15.30.45. 0.15.

:9 :10 :11 :12

40

60

80

100

120

140

Temperature (F)

1 23 

4 5 

6 

1 7 

2 

3 

 TF7: Fixture Temp 7 - Washing Machine: Rise= 16.9

 TF8: Fixture Temp 8 - Laundry Sink: Rise= 0.6

 TT4: Trunk Temp - Laundry: Rise= 17.5

 TT3: Trunk Temp - Kitchen: Rise= 0.3

 Wash Machine

 Useful GAL = 0.00 (TF > 90. )

Water 

Heater

Total Draw 

(gal)

Useful Draw 

(gal)

Useful 

Percentage

Old (Tank) 0.96 0.65 68%

Tankless 1.34 0.42 31%
43 

Figure 35. Typical kitchen sink water draw—conventional tank 

Figure 36. Typical kitchen sink water draw—tankless

02/03/13 13:09:50 GAL = 0.96

0. 5. 55.

:9 :10

0.0

0.5

1.0

1.5

2.0

Flow Rate (gpm)

DHW Site 3 

Time Since Last Draw 68.9 minutes

0. 5. 55.

:9 :10

-10

0

10

20

30

Temperature Rise (F)

 TH = Hot TC = Cold 

1 23

5 

1 6 7

 

 

02/03/13 13:09:50 Intervals=13

0. 5. 55.

:9 :10

40

60

80

100

120

140

Temperature (F)

1 2 3 

4 

5 

6 7

1 

2 3

 TF5: Fixture Temp 5 - Kitchen Sink: Rise= 60.3

 TF6: Fixture Temp 6 - Dishwasher: Rise= 21.5

 TT3: Trunk Temp - Kitchen: Rise= 54.9

 TT4: Trunk Temp - Laundry: Rise= 51.6

 Kitchen Sink

 Useful GAL = 0.65 (TF > 90. )

05/03/13 18:41:45 GAL = 1.34

40. 50. 0. 10. 20. 30. 40. 50. 0. 10.

:41 :42 :43

0.0

0.5

1.0

1.5

2.0

2.5

Flow Rate (gpm)

DHW Site 3 

Time Since Last Draw 0.3 minutes

40. 50. 0. 10. 20. 30. 40. 50. 0. 10.

:41 :42 :43

-10

0

10

20

30

Temperature Rise (F)

 TH = Hot TC = Cold 

1 23

5 

1 6 7

 

05/03/13 18:41:45 Intervals=17

40. 50. 0. 10. 20. 30. 40. 50. 0. 10.

:41 :42 :43

40

60

80

100

120

140

Temperature (F)

1 23

4 

5 

6 71 

2 3 

 TF5: Fixture Temp 5 - Kitchen Sink: Rise= 62.5

 TF6: Fixture Temp 6 - Dishwasher: Rise= 19.1

 TT4: Trunk Temp - Laundry: Rise= 64.9

 TT3: Trunk Temp - Kitchen: Rise= 64.5

 Kitchen Sink

 Useful GAL = 0.42 (TF > 90. )
44 

5.2 Impact of Distribution Retrofit at Site 1 (Group 3)

At Site 1 an HPWH was installed in April to replace the indirect hot water tank on the oilfired boiler. The monitoring was updated to measure the power use of the unit as well as the 

status of the two electric resistance elements in the HPWH tank (see Appendix B). In 

addition, the installation of the new tank shortened the 3⁄4-in. hot water distribution line by 

177 in. (which reduced the wait time by 15 seconds for a 1.5-gpm hot water draw). 

On April 10 the distribution system was further modified to include a Bell & Gossett ecorcirc 

pump. This recirculation pump includes a built-in time clock to initiate operation as well as a 

built-in temperature sensor to stop operation once return water at the pump has warmed to 

the desired set point (the setting was 85°F). The pump was installed near the tank and pulls 

water from supply lines at two remote locations: kitchen sink and half bath sink. One-half-in. 

PEX was used for the recirculation line. All total these improvements cost $2,276 to 

implement. The recirculation pump and distribution system improvements were estimated to 

be $475 of the total costs. 

The pump was scheduled operate at times when hot water use was considered probable (6:30 

to 8:30 a.m., 11:30 a.m. to 12:30 p.m., and 4:30 p.m. to 6:30 p.m. each day). Monitored 

points were added to measure the pump runtime and the return water temperature. The 

recirculation pump is allowed to operate for up to 5 hours each day, though the actual 

runtime is typically in the range of 2–5 minutes/day (average of 3 minutes/day) because of 

the pump’s internal set point threshold. Figure 37 includes 15-minute data to show how the 

trunk temperatures (TT3 to Kitchen, TT4 to the half bath) vary with pump operation. The 

fixture line temperatures are also shown (TF1 – Dishwasher, TF2 – Kitchen Sink, TF3 – Half 

Bath Sink). On this day the pump ran for about one minute to prime the lines. Subsequent 

shorter pump cycles were required to hold the return temperature (TR) near 85°F. 

Figure 37. Trunk and fixture temperatures during recirculation pump operation (Site 1 EST) 

Installing the recirculation pump and making the other distribution improvements increased 

the portion of useful hot water delivered to the end uses. Table 24 and Figure 38 show how 

05/13/13

:20 :30 :40 :50 :0 :10 :20 :30 :40 :50 :0 :10 :20 :30 :40 :50

4: 5: 6:

60

80

100

120

Temperature (F)

TT3 

TT4 

TT5 

TF1 

TF2 

TF3 

 TH

 TR

:20 :30 :40 :50 :0 :10 :20 :30 :40 :50 :0 :10 :20 :30 :40 :50

4: 5: 6:

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Pump Runtime (min)
45 

the useful portion of hot water use varied across the monitoring period. The overall useful 

portion was 78%–84% before the changes and increased to be 90%–92% after the retrofit.

The largest improvement was in the kitchen end uses. 

Figure 38. Plot showing variation of useful water draw percentage across period (Site 1) 

Table 24. Variation of Useful Water Draw Percentage Across the Period (Site 1)

Pre-Retrofit Post-Retrofit

Dec. 

2012 

Jan. 

2013 

Feb. 

2013 

Mar. 

2013 

Apr. 

2013 

May

2013 

June 

2013 Total 

Bath Sinks 40% 33% 23% 29% 30% 50% 52% 38%

Bath Showers 95% 92% 95% 95% 96% 97% 93% 95%

Kitchen 76% 69% 59% 68% 85% 96% 97% 77%

Washing Machine/

Utility 88% 91% 79% 90% 92% 97% 90% 90% 

Overall 84% 83% 78% 82% 89% 92% 90% 86%

Table 25 compares the pre- and post-retrofit performance by specific fixture. The overall 

water use and number of events were not significantly impacted by the retrofit, with the 

exception of the kitchen sink, which did show a significant drop in hot water use. Other 

changes at the fixture level were attributable to occupancy differences in the two periods. 

Some improvement in the portion of useful hot water was noted for the kitchen sink (from 

63%–97%) with less improvement noted for the half bath sink (21%–30%), utility sink 

(53%–66%), and dishwasher (90%–98%).

Modest improvements were also noted for the master bath sink (28%–35%) and the bath 2 

sink (49%–66%), which were not enhanced by the recirculation pumps directly. However, 

the reduction in piping length (177 in.) with the new water heater location and the modest hot 

water priming of the first 30–40 in. of the piping near the tank both contributed to the 

improvement. 

0%

20%

40%

60%

80%

100%

120%

Portion of Draw that is "Useful"

Bath Sinks

Bath Showers

Kitchen

Wash Mach/Utility

Overall
46 

Table 25. Impact of Retrofit on Events and Total Hot Water Use at Site 1 

(Pre-Retrofit; Post-Retrofit) 

Events per Day Total Hot Water Use 

(gpd) Useful Portion

PreRetrofitPostRetrofit Notes PreRetrofitPostRetrofit Notes PreRetrofitPostRetrofit Notes

Dishwasher 1.5 1.3 2.7 2.4 90% 98%

Kitchen Sink 17.0 13.0 9.1 5.6 63% 97% Recirc 

pump

Half Bath Sink 2.1 3.0 0.7 1.0 21% 30% Recirc 

pump

Washing Machine 0.7 1.1 9.1 12.7 91% 94%

Utility Sink 0.3 0.4 0.9 0.4 53% 66% Recirc 

pump

Master Sink 6.8 4.2 2.2 1.2 28% 35% Shorter 

run

Master Shower 1.5 1.4 17.8 13.3 95% 97%

Bath 2 Sink 1.7 1.3 1.2 1.6 49% 66% Shorter 

run

Bath 2 Shower 0.7 0.8 8.4 9.9 91% 93%

Unclassified 36.8 44.9 3.4 7.5 – –

69.4 71.3 55.4 55.6 82% 91%
47 

5.3 Impact of Distribution Retrofit at Site 2 (Group 3)

At Site 2 a new AO Smith Vertex (GDHE-50) condensing storage tank water heater was 

installed (very close to the location of the original water heater) on May 21, 2013. At the 

same time a Taco SmartPlus recirculation pump was installed on the supply line with the 

sensor downstream of the pump. A 1⁄2-in. PEX return line was added from the supply line 

under the kitchen sink back to the cold water inlet to the water heater. The water heater and 

all improvements were installed by a city-licensed plumber for $5,170. The recirculation 

pump and return line were estimated to be $988 of the total installation.

The pump was set in the “Smart/Learn Mode,” where it runs based on the pattern established 

over the last 7 days of operation. In this Smart Mode, the pump runs in the Pulse Mode 

(running for 2.5 minutes out of every 10 minutes) for a 2-hour window centered around each 

draw observed/recorded 7 days ago. 

The measured runtime for the pump was about 200 minutes/day (about 14% of the time). The 

“Smart/Learn Mode” reduced the runtime by only a modest amount compared to the “Pulse 

Mode,” which would have run the pump 25% of the time 24 hours/day. In contrast, the timercontrolled pump at Site 1 runs the pump only about 3 minutes/day in the 5-hour window 

when operation is enabled. 

Water use at this site was highly variable across the monitoring period as shown in Figure 39, 

implying that the number of occupants in the house frequently changed. This confounded 

some of the pre- and post-retrofit comparisons below. 

0

10

20

30

40

50

60

70

80

90

Dec-12 Jan-13 Feb-13 Mar-13 Apr-13 May-13 Jun-13

HW Use (gal/day)

Wash Mach/Utility

Kitchen

Bath Showers

Bath Sinks

Figure 39. Plot showing variation of water use across monitoring period (Site 2)
48 

The substantial runtime of the recirculation pump greatly increased thermal losses from the 

system and lowered the effective daily water heating efficiency1 to 0.40–0.70, depending on 

hot water use (see Figure 40). Based on laboratory data for this same water heater unit, the 

expected daily water heating efficiency for this system is about 0.85 at 64 gpd (see 

Henderson et al. 2013). 

Figure 41 shows the measured delivered thermal output supplied by the unit versus the 

measured natural gas input. The data show some scatter since the occupants frequently used 

water late at night (and gas consumption for recovery occurs on the next day). However the 

data show that the standby losses for the system are approximately 20 MBtu/day (i.e., the 

fuel input with no water use). 

Laboratory measurements for the same unit indicated that standby losses for the tank alone 

were 6.9 MBtu/day. From this difference we can infer that operation of the recirculation 

pump increases daily gas use by about 14 MBtu/day. Assuming a marginal unit efficiency of 

0.85–0.90 for the system, the added thermal losses are about 15–16 MBtu/day. 

 

1 Daily water heating efficiency is integrated thermal energy supplied by the unit divided by the fuel energy 

input over the day. The recirculation pump operation did not affect this value (since it did not induce any 

makeup water flow).

05/21/13 to 10/31/13

0 50 100 150 200 250 300

Water Use (gal/day)

0.2

0.4

0.6

0.8

1.0

Daily Water Heating Efficiency (-)

Laboratory Efficiency is 0.85 

at 64 gal/day

Figure 40. Daily system efficiency as a function of hot water use (Site 2) 
49 

Figure 41. Plot showing thermal input versus thermal output (Site 2) 

In spite of the high thermal losses, installing the recirculation pump appeared to have very 

little impact on hot water distribution performance at this site. The portion of useful hot water 

delivered to the end uses was not noticeably different in the pre- and post-retrofit periods. 

Table 26 and Figure 42 show how the useful portion of hot water use varied across the 

monitoring period. No positive change was apparent. 

05/21/13 to 10/31/13

0 50 100 150

INPUT: Gas Use (MBtu/day)

0

20

40

60

80

100

120

OUTPUT: Supplied Heat (MBtu/day)

0%

20%

40%

60%

80%

100%

120%

Portion of Draw that is "Useful"

Bath Sink

Bath Shower

Kitchen Sink

Washing Mach

Overall

Standby Losses with 

Recirculation Pump (~20 

MBtu/day)

Standby Losses for Unit in 

Laboratory (6.9 MBtu/day)

Figure 42. Plot showing variation of useful water draw percentage across period (Site 2)
50 

Table 26. Variation of Useful Water Draw Percentage Across Period (Site 2)

Pre-Retrofit Post-Retrofit

Dec. 

2012 

Jan. 

2013 

Feb. 

2013 

Mar. 

2013 

Apr. 

2013 

May

2013 

June 

2013 Total 

Bath Sink 99% 92% 99% 97% 96% 92% 89% 93%

Bath Shower 86% 98% 100% 100% 97% 72% 100% 91%

Kitchen Sink 60% 49% 73% 51% 74% 44% 57% 59%

Washing Machine 70% 56% 63% 52% 57% 45% 48% 52%

Overall 84% 94% 95% 96% 94% 72% 96% 88%

Table 27 compares the pre- and post-retrofit performance by specific fixture. The overall 

water use and number of events were not significantly impacted by the distribution retrofit. 

Table 27. Impact of Retrofit on Events and Total Hot Water Use (Site 2) 

(Pre-Retrofit; Post-Retrofit) 

Events per Day Total HW Use (gpd) Useful Portion

PreRetrofitPostRetrofitPreRetrofitPostRetrofitPreRetrofitPostRetrofit

Bath Sink 4.0 4.0 4.8 9.9 96% 88%

Bath Shower 3.2 3.3 41.9 54.8 89% 99%

Kitchen Sink 2.3 1.6 3.0 2.6 62% 59%

Washing Machine 2.0 2.5 1.3 4.0 56% 48%

Unclassified 18.2 7.6 1.0 0.7 – –

29.6 19.0 52.0 72.0 87% 93%
51 

6 Conclusions

Surface-mounted temperature sensors were installed on trunk lines as well as branch lines to 

each hot water fixture in five existing houses to both disaggregate hot water use and assess 

the portion of each hot water draw that was deemed useful (i.e., exceeded 90°F). Data were 

collected during hot water draws at 5-second intervals in order to track temperature changes 

and understand the flow variations during the draw. In some cases wireless data loggers were 

used to reach fixture piping located in remote locations in the house. 

At two of the houses no changes were made (Group 1, Sites 4 and 5). At three of houses, 

changes were made to the hot water systems after a few months of data collection:

• Group 2. At Site 3, a tankless water heater was installed to assess the impact on 

distribution performance. 

• Group 3. At Sites 1 and 2, new water heaters were installed and recirculation pumps

were added to improve hot water distribution performance. 

6.1 Disaggregation and Useful Hot Water Delivery

Simple rules about temperature level and temperature rise were developed and automated to 

disaggregate hot water loads, or to assign each hot water draw to a given fixture based on the 

temperature measurements on the trunk and fixture piping. Using this approach we were able 

to classify only 17%–57% of the hot water draw events in each of the five homes. However, 

the process was able to classify 88%–98% of the total water use in these homes. The house 

with the lowest level of classification (Site 4) had an average of 180 draws and used 115 

gpd—most of these draws were of very short duration. The house with the highest level of 

classification (Site 5) averaged about 26 draws and used 46 gpd. 

The temperature data were also used to assess the portion of each hot water draw that was 

deemed “useful”; i.e., exceeded a certain temperature threshold at the fixture or trunk 

location. We used a threshold of 90°F at the fixture and 100°F at trunk lines leading to the 

fixture to gauge “usefulness.” We also evaluated the impact of using higher and lower 

temperature thresholds to gauge “usefulness.” 

By this method, amount of hot water that could be deemed as useful ranged from 75% ± 5% 

at Site 4 to 91% ± 2% at Site 5. The average for the five houses before retrofit was 85%. The 

probable error in the determination of “usefulness” was estimated to be ± 2% for Sites 1, 2, 3, 

and 5 with copper piping and ± 5% at Site 4 with PEX piping. The fixtures with the lowest 

fraction of useful hot water were typically kitchen and bathroom sinks. 

6.2 Retrofit Impacts

At Site 3 a tankless water heater was installed after 3 months of monitoring with a 

conventional water heater. The occupants changed their hot water use behavior after the 

tankless unit was installed. The number of hot water draw events per day was cut in half. 

Most of this change occurred at sinks, where small duration events were eliminated. 

Overall hot water use showed no perceptible change after the tankless unit was installed. The 

overall percentage of useful hot water use decreased from 90%–91% with the conventional 
52 

tank to 84%–86% with the tankless unit. This reduction in useful delivered hot water was 

mostly due to the 40-second startup delay of the tankless unit, which resulted in less hot 

water being delivered to the faucet. The largest reduction in usefulness was associated with 

the kitchen, bath sinks, and laundry end uses. 

The homeowners at Site 3 also purchased a high efficiency washing machine about 5 weeks 

after the tankless water heater was installed. When the tankless unit was working with the 

original washing machine it behaved in an unexpected way: cycling the burner on and off 

even though the hot water flow remained well above the minimum cutout flow of 0.26 gpm. 

The result was that a limited amount of hot water was delivered to the appliance. When the 

new high efficiency washer was used, the pulsed water demand profile of the appliance 

resulted in almost no hot water being delivered to the device. 

At Site 1 a new HPWH was installed in a new location that shortened the 3⁄4-in. hot water 

supply line by 177 in. In addition, a Bell & Gossett ecocirc recirculation pump with timeclock controls and an internal temperature sensor was added along with a return line pulling 

water from two remote locations (kitchen sink and half bath). The pump was enabled to 

operate for three key periods totaling 5 hours each day. On average the pump operated only 

about 3 minutes each day to prime the hot water lines. The pump installation cost about $478. 

The overall useful portion of delivered hot water was 82% before the changes. The useful 

portion increased to 91% after the retrofit. The largest improvement was in the kitchen end 

uses, where typical waits for hot water had previously been very long. Modest improvements 

were also noted at other fixtures (not served by the pump) due to the shorter hot water supply 

line (i.e., 28%–35% for the master sink and 49%–66% for the bath 2 sink). 

Site 2 had a new condensing water heater tank installed along with a Taco SmartPlus 

recirculation pump. The pump installation cost $988. The pump was set to operate in the 

smart mode, where it anticipates when to operate the pump based on the previous 7-day 

operating pattern. This pump was observed to operate about 200 minutes/day or about 14% 

of the time. This excessive runtime on the pump resulted in significant thermal losses. The 

water heater, which in the laboratory had standby gas use of 6.9 MBtu/day for the tank alone, 

operated with standby losses of 20 MBtu/day with the recirculation pump operating in the 

field. 

The recirculation pump had no perceptible impact on the useful portion of delivered hot 

water. The large variations in hot water use across the pre- and post-retrofit periods (due to 

changes in occupancy) may have partially obscured the impact of adding the recirculation 

pump. 

6.3 Addressing the Research Questions

The following answers to the research questions were determined from this field research

project: 
53 

QUESTION: What is the magnitude of hot water waste for existing homes in the 

Northeast, considering a variety of water heating systems (i.e., tankless and storage 

tank)?

Overall average hot water waste was found to be in the range of 9%–25% at the five houses. 

Houses with new additions (Sites 1 and 4) tended to result in longer piping runs that resulted 

in more hot water waste. Smaller homes with their original, compact floor plans intact had 

less hot water waste. 

What constitutes a “typical” distribution system in the Northeast? How does it compare 

to systems in other regions of the United States? 

Houses in this study were all older homes with water heaters and piping located in basements

(with some piping in crawlspaces). All homes were either two-story or raised ranch. Many 

had been substantially retrofitted or had new additions added. No piping was in the slab. In 

some cases very old steel piping was still hidden in the walls. Most exposed piping in the 

basement was converted (or was originally installed) copper or PEX. 

What improvements or remediation can be cost-effectively implemented in a DHW 

retrofit to reduce hot water waste and energy use, focusing on hot water system 

configurations commonly found in older single-family homes in the Northeast?

At one house (Site 1) placement of an indirect water heater tank near the space heating boiler 

resulted in a long hot water piping supply run. Installation of a new HPWH closer to the 

center of the hot water piping arrangement resulted in a 177-in. reduction in the 3⁄4-in. hot 

water supply trunk. At this same site, adding a 1⁄2-in. PEX recirculation line and pump to the 

remotely located kitchen fixtures had a significant impact on the portion of hot water delivery 

that was deemed useful. 

Other houses (Site 2) with centrally located plumbing did not seem benefit from a 

recirculation pump, especially when the pump controls led to excessive pump runtime. As 

with commercial installations, controls that operate the pump only a few minutes per day 

have the best impact on hot water delivery performance.

6.4 Lessons and Recommendations

Adding a recirculation pump and return line was demonstrated to increase the “usefulness” 

and reduce hot water wait times at the expected fixtures in a recently remodeled home with 

long piping runs. However, at a smaller home with a more centralized floor plan, no change 

in “usefulness” was observed. At both these homes, no detectable change in hot water use or 

energy use was observed. Clear evidence of greater system standby losses were linked to 

prolonged recirculation pump operation at the smaller home. The $478–$988 investment for 

this recirculation system improved home owner satisfaction at least in one case but did not 

provide any clear evidence of energy cost savings in the first few months of system 

operation. 
54 

Based on this study we make the following recommendations: 

• Monitoring should continue at these test sites for at least 12 months to confirm the 

initial findings, specifically to further assess if hot water use is reduced with increased 

“usefulness.” 

• Further research is required to understand the situations and house configurations 

where recirculation pumps may provide the energy savings and/or improved occupant 

satisfaction with hot water delivery. 
55 

References

Barley, C.D.; Hendron, R; Magnusson, L. (2010). “Field Test of a DHW Distribution System: 

Temperature and Flow Analyses.” Presented at ACEEE May 2010 Hot Water Forum. Golden, 

CO: National Renewable Energy Laboratory, NREL/PR-550-48385. 

Chinery, G.T. (2006). “Policy Recommendations for the HERS Community To Consider 

Regarding HERS Scoring Credit Due to Enhanced Effective Energy Factors of Water Heaters 

Resulting From Volumetric Hot Water Savings Due to Conservation Devices/Strategies.” 

Presented at meeting of EPA ENERGY STAR® for Homes, December. 

Henderson, H.; Bogucz, E.A.; Wade, J.; Straile, C. (2013). Evaluating Domestic Water Heater 

Performance for NY Homes. Albany, NY: NYSERDA. 

http://cloud.cdhenergy.com/dhw_coe/documents/reports/Laboratory_Test_ResultsReport_1_Nov2013.pdf 

Hendron, R.; Burch, J.; Hoeschele, M.; Ranier, L. (2009). “Potential for Energy Savings through 

Residential Hot Water Distribution Improvements.” Proceedings of the 3rd Annual International 

Conference on Energy Sustainability. Paper ES2009-90307. San Francisco, CA. 

Klein, G. (2005). “Hot-Water Distribution Systems – Part III.” Plumbing Systems & Design, 

May/June. 

Klein, G. (2006). “Saving Water and Energy in Residential Hot Water Distribution Systems.” 

Slides from California Energy Commission at DOE website.

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

Systems.” Berkeley, CA: Lawrence Berkeley National Laboratory, LBNL-57199. 

Magnusson, L. (2009). “Methods and Results for Measuring Hot Water Use at the Fixture.” 

Golden, CO: National Renewable Energy Laboratory. Presented at ACEEE June 2009 Hot Water 

Forum. 

RECS (2005). Residential Energy Consumption Survey. Table 13. www.eia.doe.gov/emeu/recs/. 
56 

Appendix A: Literature Review

A1 Review of the Literature

A1.1 Identification and Bounding of the Problem

Gary Klein a wrote a three-part series of articles on hot water distribution systems for Plumbing 

Systems & Design magazine from the American Society of Plumbing Engineers in 2005 (Klein 

2005a, 2005b, 2005c). This series of articles provides a very good explanation of the concept and 

problem of hot water waste. In Part I he points out that the issue of long wait times for hot water 

to arrive at your fixture is tied to newer homes (built since 1970) that have been built based on 

newer plumbing codes. He points out that in newer homes: 

• Piping increased from 1⁄2 in. to 3⁄4 in. 

• Piping layouts moved from radial arrangement to trunk-branch. 

• More fixtures in the house are farther away from the water heater. 

He makes the case that these factors have increased wait times for hot water by a factor of 18 

compared to old houses. He also lays out a thought exercise demonstrating that hot water waste 

is probably on the order of 10%–30% (or 5–20 gpd). Hot water waste is related to the actual wait 

time for hot water as well as the behavior of occupants in response to that time delay (which 

often makes the hot water waste even worse).

Part II discusses what people want and expect from their water heater and distribution system:

namely safety and convenience. The safety concerns include the water not being too hot (to 

cause scalding) or too cold (so harmful bacteria can grow). Consumers also value the 

convenience of being able to adjust temperature and flow and expect an unlimited or continuous 

supply of hot water. 

The article also describes a manifold/homerun system architecture—with 1⁄2-in. or 3⁄8-in. piping 

running from a central point to each fixture—as a partial solution to reducing water waste. He 

points out that the reduction in water waste can be about 50%, but there can be usage patterns 

that can often result in more waste.

Part III talks about the concept of recirculation loops and compares them to other less practical 

options (such as heat tracing). He describes that recirculation pumps can run continuously, can 

run based on a timer, or be based on the recirculation return water temperature. He points out 

that demand control of the pump has a much lower energy cost. He points out that demand can 

be sensed using buttons at the sink, occupancy sensors, or flow switches (but he provides no 

discussion as to which demand control option is better).

A1.2 Products on the Market to Reduce Water Waste and Distribution Losses

Hot water recirculation pumps are widely used in commercial and multifamily buildings.

However, there have historically been fewer products for single-family homes. Some residential 

products are now available where the pump sits under the sink and pumps cooled water from the 

hot water lines into the cold water line or, alternatively, back toward the water heater. 
57 

The Metlund D’MAND hot water pump from Advanced Conservation Technology, Inc.

(www.gothotwater.com ) is one of the most prominent options for residential recirculation 

pumps (Acker and Klein 2006; Acker 2009). The most common retrofit application is with the 

pump mounted under the bathroom sink at the location farthest from the water heater. The pump 

moves cooled water from the hot water piping into the cold water piping at this fixture. Pump 

operation is operator-initiated by an occupancy sensor, a remote control, or button near the sink. 

The pump turns off when the temperature at the pump increases by 6°F. 

Manufacturers such as Taco (www.taco-hvac.com) offer traditional commercial-style 

recirculation pumps that can be controlled by either a temperature sensor (aquastat) on the return 

line and/or a timer that operates the pump only at high demand times. The timer and control 

functions are integrated into the pump body. Taco also appears to have licensed the D’MAND 

pump technology from Advanced Conservation Technologies, Inc. as one of its available product 

options. 

In addition Taco has recently introduced its SmartPlus system that senses usage by measuring the 

system supply temperature and then “learns” the 7-day draw pattern and keeps applying it to 

subsequent 7-day periods. It also has the ability to detect vacations and stop operation after a few 

days. It can be installed near the water heater and does not require sensors at fixture locations. It 

does require that a return line be added to the system. 

The Grundfos Comfort System has a timer initiated pump and a thermal valve that mounts under 

the farthest sink (http://us.grundfos.com/products/find-product/comfort-pumps-up-10.html). This 

pressure boost pump is intended to mount on the outlet of the water heater. The thermal valve 

mounts under the sink between the hot and cold water lines. When the valve is cool, a bimetallic 

element opens and allows flow from the hot to cold side. The valve starts to close at 93°F and is 

fully closed at 103°F. The pump is activated to provide a pressure boost by the on-board timer. 

The pump (apparently) goes off when the pressure increases as the thermal valve closes. The 

system has the advantage of not requiring the pump to be located under a bathroom sink; instead 

the pump is installed at the water heater (where 120 VAC power is more likely to be available).

Some users report that the valve must be replaced every few months, though the price of these 

valves is relatively modest.

Similarly Bell & Gossett produces recirculation pumps (ecocirc) that use electronically 

commutated motors (ECMs) so that pumping power is very low. It includes options for timer and 

aquastat control and is designed to be installed in a dedicated return line. The autocirc model also 

includes built-in timers and thermostats to control pump operation. It is designed to mount under 

the fixture that is farthest from the water heater.

All these systems appear to be marketed to consumers based on convenience and comfort of 

instant hot water at the fixture instead of energy savings. Only the D’MAND system offers 

occupant-initiated pump operation, which is expected to have the lowest energy impact. No 

residential products appear to offer the control method of using a flow switch on the makeup 

water line – the approach that is often used in large multifamily buildings. However the Taco 

SmartPlus system does appear to use the supply temperature as a low cost surrogate for sensing 

demand (at least after the fact). Table 28 summarizes the key features of these different systems.
58 

Table 28. Summary of Residential Recirculation Products on the Market 

A1.3 Laboratory Measurements of Piping Losses and Flow Patterns

Klein (2006a) also discusses the results of Hiller (2005) that was funded by the California 

Energy Commission (CEC). Several types of hot water piping (copper, PEX, and PEXAluminum-PEX) at several sizes (1⁄2 in. and 3⁄4 in.) were tested in a laboratory setup to measure 

heat loss and temperature reductions with different flow rates. The impact of insulation was also 

evaluated. The tests revealed some expected and unexpected results. One unexpected finding was 

that slip flow – with less dense hot water slipping over the top of the cold water – occurred at 

low flow rates. The slip flow profile doubled the volume of water required before a full profile of 

hot water could reach a fixture, compared to simple plug flow.

A1.4 Field Measurements of Distribution Losses and Baseline 

Usage/Characteristics

Hiller (2005) also surveyed about 28 California homes to understand common installation 

practices for hot water distribution systems. He found that the length and volume of under slab 

piping was much greater than expected and greater than that of above ground piping. Hot water 

piping is normally run in the same trenches as the drainage pipes for each fixture which usually 

runs parallel and perpendicular to structure. This is rarely the shortest distance between fixtures.

Straight runs between fixtures under the slab would have substantially reduced the piping length.

Minimal insulation was installed in tract built homes, but in custom built homes the majority of 

the hot water piping was insulated. However, the insulation was poorly installed with elbows 

completely lacking insulation. The under slab piping environment was found to be very moist to 

wet with standing water in most cases. He also noted that the hot and cold piping were typically 

bundled together. 

The Davis Energy Group (Hoeschele and Chitwood 2006) also surveyed 60 production built 

homes in California to gather information about the hot water distribution systems. This effort 

Manufacturer/

Trade Name(s)

Pump Installation 

Location

Control Activation and

Shutoff Other

ACT, Inc.

Metlund D’MAND

Under sink or in return 

line

Occupant initiated, off 

on temperature rise

Taco

Plumb n’ Plug

Near water heater, 

return line Timer and/or aquastat

Taco

SmartPlus 

Near water heater, 

return or supply line 

Supply line sensor, 

“learns” 7-day pattern

Bell & Gossett

ecocirc

Near water heater, 

return line Timer ECM10 Watts

Bell & Gossett

autocirc Under sink Timer and thermostat ECM

14 Watts

Grundfos

Comfort System

Near water heater,

supply line Timer Thermal valve under fixture
59 

was part of a larger effort with LBNL that was funded by the CEC (Lutz 2008). The survey 

gathered extensive information including site and water heater characteristics, developed 

sketches and tabulations of piping systems, points of use and fixture type, and under slab soil and 

pipe environment characteristics. The recirculation system and control method was also noted 

when applicable. The survey revealed that new homes were growing in size and the number of 

hot water end use points was increasing. 

The American Water and Wastewater Association Research Foundation sponsored the 

Residential End Uses of Water Study (REUWS) in the late 1990s (Mayer et al. 1999). This study 

collected very detailed water end use data from 1200 single-family homes in 12 North American 

locations from 1996 to 1998. The REUWS installed a flow meter on the main water meter and 

collected data at 10 second intervals. The study used flow trace analysis software to assign the 

individual draws to the appropriate end use or fixture (hot or cold). The REUWS database 

contains the total volume of water used, duration of each draw, and the peak and mode (i.e., most 

commonly recorded) flow rates for the draw. The database includes nearly 2 million draw events. 

Lutz (2005) estimated the amount of wasted hot water in North American homes using the data 

from the REUWS database. Lutz estimated the water and energy waste for three types of water 

draw events:

• Hot water that runs down the drain before it can be used (e.g., shower)

• Hot water that cools down in the distribution system after a draw (e.g., short sink draws), 

• Hot water that cools down and must be reheated (e.g., dishwasher). 

Lutz developed methods to analyze data from the REUWS database to estimate the amount of 

waste associated with each type of loss. For instance, he analyzed nearly 49,000 shower hot 

water events and estimated that the average volume of hot water wasted at the beginning of each 

shower draw was 3.48 gal, or about 20% of the average shower. Similarly he estimated the waste 

associated with sink draw events. Short draws often do not allow useful heat to even reach the 

fixture. Losses at the dishwasher do not include water losses, but equate to additional energy that 

is required to reheat the water. All total these losses were estimated be 10.7 gpd or about 20% of 

52.6 gpd used in an average home. 

Lutz et al. (2008) gathered together and used 1-minute interval data available from multiple field 

studies to develop an hourly profile for hot water use. This effort was intended to develop an 

improved water use profile for the CEC in order to support the efforts to update the Title 24 

energy efficiency standards. They developed an end use profile that was close to the ASHRAE 

90.2 profile, with slightly less morning use. The profile is shown below in Figure 43. 
60 

Figure 43. Comparing various hot water use profiles from Lutz et al. (2008). Blue bars are the 

results from Lutz et al.; red bars are from ASHRAE 90.2; yellows bars are from Becker (1990) 

Hoeschele et al. (2009) recently worked with the Gas Technology Institute (GTI) to field test 

several higher efficiency gas water heaters at 18 single-family homes in California. Each home 

was monitored with the original system for 4 months and then retrofit with a more efficient gas 

water heater. A range of water heaters were installed, including ENERGY STAR units (EF = 

0.67–0.70), non-condensing tankless, condensing tankless, and high efficiency condensing 

storage units. The field testing gathered fuel, energy, and water use data at 15-minute intervals to 

assess efficiency and energy use. These data were used to evaluate technical and economic 

performance of the various higher efficiency options. Detailed data, down to a 4-second 

resolution, were also collected on each water draw to understand the water consumption pattern 

and draw details.

A1.5 Analysis Techniques to Indirectly Measure Hot Water Use at Fixtures 

As mentioned above, the REUWS measurements (Mayer et al. 1999) determined water use at 

each end use or fixture using direct measurements at the main meter combined with a flow trace 

analysis method. They used the Aquacraft Trace Wizard software, which is a commercially 

available software tool that uses flow trace data collected from a main meter to allocate each 

draw to a fixture or end use (www.aquacraft.com). The approach has been widely used to 

disaggregate residential water uses in hundreds of homes. A recent study of California houses is 

representative of the use of this method (DeOreo et al. 2011). 

NREL monitored several homes in detail, installing a flow meter on each end use. This field 

testing was presented by Magnusson (2009) and then Barley et al. (2010) at the ACEEE Hot 

Water Forum. The Aquacraft Flow Trace method of assigning flows to each fixture was also 

implemented and compared to the actual measurements. In addition, the method of using a 

temperature probe attached the pipe near each fixture to detect the direction of flow was also 
61 

implemented at the sites. This temperature method was first described by Weihl and Kempton 

(1985). Data at these sites were collected at 1-second intervals. 

Figure 44 compares the actual flow measurements at each fixture to the predicted values from 

the Aquacraft software. While the Aquacraft results are fairly good, some errors were apparent.

Figure 44. Plot from Magusson (2009) comparing direct measurements of hot water flow events 

(square) to Aquacraft results; Aquacraft method was good but did have some error.

Barley et al. (2010) analyzed the errors of the flow trace and temperature methods of flow 

disaggregation and demonstrated that the errors of the two methods were similar. He noted that 

the temperature method might therefore be preferable because it provides the additional 

information of temperatures at the fixture. The temperature data can be used to further determine 

time delays and water waste associated with each fixture.

Researchers at the University of Washington (Larson et al. 2010) have developed a lessobtrusive measurement technique to disaggregate water draws and assign then to specific fixtures 

using a pressure signature method. Total water use is measured at the main meter. A pressure 

transducer (usually installed on a hose barb) measures the pressure response in the frequency 

domain. A draw at each fixture produces a unique signature that can be used to assign measured 

water use to that end use. Possibilities for distinguishing simultaneous draws at multiple end uses 

also exist. 

A1.6 Field Measurements of Distribution System Improvements

One of the first studies of demand recirculation systems was a field test of five Palo Alto, 

California homes by Ally et al. (2002). These homes had new water heaters installed along with 

the D’MAND hot water pumps from Metlund (www.gothotwater.com ). The pumps were 
62 

mounted under the bathroom sink to pump cooled down water from the hot water piping to the 

cold water piping at this fixture. Pump operation is initiated by an occupancy sensor, remote 

control, or button under the sink. The pump turns off when the temperature at the pump increases 

by 6°F.

The homes had Btu meters and water flow meters installed that were manually read by the 

homeowners. The study had problems with reliable data collection but was able to estimate hot 

water savings in the range of 11%–30% in the winter months, and typically about one third of 

that amount in the summer months. Energy savings were probably less than this amount since 

this water still cools down and is ultimately consumed as cold water (their energy data were 

inconclusive). 

Barley et al. (2010) retrofitted a highly instrumented house in Boulder, Colorado with 

recirculation pumps at three fixtures that returned water back to the tank. The pumps were 

activated by occupancy sensors and shut off based on a temperature rise at the pump. This house 

had a solar hot water system with an electric auxiliary tank. Operating the recirculation pumping 

system reduced hot use by 14%, but did not result in electric energy savings. They reported that 

the unexpected results may have been caused by interactions with the solar system.

Building Science Corporation (2005) also measured hot water wait times at some of its test 

homes in California with and without a continuous recirculation pump operating. This testing 

demonstrated that continuous pump operation resulted in significant water savings in these larger 

homes, where wait times for hot water had been significant. While energy use was not measured 

in these short-term tests, Building Science Corporation acknowledged that the energy impact of 

continuous pump operation would be significant. 

A1.7 Modeling to Simulate Distribution System Performance, Losses and 

Improvements

Davis Energy Group (Springer et al. 2008; DEG 2007) developed the HWSIM software to 

simulate the performance of a hot water distribution system. The software was originally 

developed in 1990 as part of a CEC project to develop a comprehensive methodology for 

evaluating Title 24 Residential Energy Efficiency Standards. In 2004 the model was upgraded to 

consider hourly variations in environmental temperatures across a representative week in each 

month. Inlet water temperatures can be specified for each month. The model can consider 

various types of draws from any fixture or end use point. The draw can be specified several 

different ways (a specified hot water flow and duration; a hot water flow to maintain a 

temperature set point at the end use, etc.). Hundreds of draws can be defined and managed to 

build up a typical use profile. The amount of “useful” hot water delivered can be defined by 

setting a minimum acceptable delivery temperature.

The thermal model uses a finite difference method at short time intervals to predict temperatures 

within the distribution system piping. The piping system is discretized into nodes or volume 

elements that are on the order of 0.01 gal. Water-to-pipe heat transfer is assumed to be turbulent. 

Pipe-to-air heat transfer assumes still air surrounds the pipe. The software includes libraries of 

geometry property data for commonly used pipe and insulation materials. The hot water outlet 

temperature performance characteristics from the water heater can also be defined as can 
63 

recirculation loop geometry, flow, and controls. The software can simulate a larger number of 

draws across the year. 

The model calculates key performance metric on an annual and monthly basis such as delivered 

energy, distribution efficiency, wasted or unusable hot water, etc. The HWSIM has been verified 

by comparing its predictions to the measured laboratory data on piping heat loss collected by 

Hiller (2005). 

NREL (Maguire et al. 2011) has also developed models in TRNSYS to simulate the thermal 

performance of a hot water distribution system. They developed this model to provide the 

following features that are not available with the current version of HWSIM: 

• To allow for an entire year of multiple unique water draw events, entering water 

temperatures, and different environmental temperatures 

• To simulate the detailed performance of the conventional and solar water heaters using 

the component libraries in TRNSYS 

• To allow for the eventual integration of hot water distribution and building environmental 

conditions into a common model. 

The transient model is very similar to HWSIM from a thermal point of view, but constructing the 

model in the TRNSYS environment provides flexibility that is not available in the HWSIM 

software, with its well-developed user interface.

Hendron et al. (2009) used the HWSIM model to predict the annual energy savings of various 

water heating distribution improvements. They looked at various insulation and recirculation 

pump control options in two different climates (Tampa and St. Louis). 

NREL (Hendron et al. 2010) has developed a spreadsheet tool to generate a set of cold and hot 

water draws at each fixture over the course of a year. The draw events of both cold and hot water 

flow – starting at a certain time with flow and duration at each fixture – are stochastically 

generated to represent the defined characteristics of a household. The number of draw events and 

daily water use ranges can vary for each day. The number of events is on the order of 20–50/day.

The tool is intended to generate the hot draw input schedules for hot water distribution system 

simulation tools such as those described above. 

A2 Lessons for This Project

As part of the ARIES Project, we retrofitted two existing hot water systems while measuring 

performance both before and after the system change. The retrofits included distribution system 

improvements to reduce hot water waste due to distribution system losses. Based on this 

literature review we draw the following lessons relevant to this field testing effort:

• There are two recirculation systems that seem most appropriate for the retrofit sites: (1) 

the Metlund D’MAND pump that incorporates occupancy controls to activate the pump; 

and (2) the Taco SmartPlus system that senses a weekly demand pattern and then brings 

the pump on in response to that “learned” 7-day schedule. 
64 

• Lutz (2005) and Barley et al. (2010) point out that disaggregation of hot water end uses 

using temperature is the most accurate method. The ARIES project used this approach to 

disaggregate draws and assign them to the various end uses. Temperatures were used to 

determine the time delay for hot water to reach a fixture.

• Lutz (2005) demonstrated how the plot of water flow rate versus total water use for each 

draw is useful for classifying types of hot water draws. This analysis approach was used 

to evaluate the data collected in this project. 

• To make the field data collected from these sites useful to other researchers that may 

want to simulate the performance of these systems in the future, we documented each 

home and collected characteristic data in a similar format that was used by the Davis 

Energy Group for its 60 home California study (Hoeschele and Chitwood 2006). We also 

collected ambient temperature data in locations where key piping runs are located.
65 

A3 References

A3.1 Trade Press Articles

Acker, L. and G. Klein 2006. Benefits of Demand Controlled Pumping. Home Energy Magazine.

September/October. Pp. 18. 

Klein, G. 2005a. Hot-Water Distribution Systems – Part I. Plumbing Systems & Design. 

American Society of Plumbing Engineers. January/February. 

Klein, G. 2005b. Hot-Water Distribution Systems – Part II. Plumbing Systems & Design. 

American Society of Plumbing Engineers. March/April.

Klein, G. 2005c. Hot-Water Distribution Systems – Part III. Plumbing Systems & Design.

American Society of Plumbing Engineers. May/June.

Klein, G. 2006a. Hot Water Distribution Research. Plumbing Systems & Design. American 

Society of Plumbing Engineers. September/October.

A3.2 Product Literature

Bell & Gossett. http://completewatersystems.com/2011/01/new-bell-gossett-autocirc-pumpprovides-instant-hot-water-to-any-faucet/ 

D’MAND pump. www.gothotwater.com 

Grundfos Comfort System 

http://us.grundfos.com/products/find-product/comfort-pumps-up-10.html 

Taco Pump Instant Hot Water Options 

http://www.taco-hvac.com/products.html?current_category=360 

A3.3 Presentations, Papers, Reports

Ally, M.R., J.J. Tomlinson, B.T. Ward. 2002. Water and Energy Savings using Demand Hot 

Water Recirculating Systems in Residential Homes: A Case Study of Five Homes in Palo Alto, 

California. Oak Ridge National Laboratory. ORNL/TM-2002/245. September.

Acker, L. 2009. Smart Controls. Presented at ACEEE Hot Water Forum, Berkeley, CA. Session 

7A.

Becker, B.R. and K.E. Stogsdill, 1990. “Development of Hot Water Use Data Base.” ASHRAE 

Transactions, Vol. 96, Part 2, pp. 422-427. American Society of Heating, Refrigerating and Air 

Conditioning Engineers, Atlanta, GA. 

Barley, C.D., R Hendron, L. Magnusson. 2010. “Field test of a DHW distribution system: 

temperature and flow analyses.” Presented at ACEEE May 2010 Hot Water Forum. NREL/PR, 

550-48385. 

Building Science Corp. 2005. Wait and Waste Testing of D.R. Horton Beta Home
66 

Davis Energy Group. 2007. HWSIM Hot Water Distribution Model Validation Report.

Subcontract# 6803947 with LBNL. APPENDIX M of CEC-500-2005-007-APA.

DeOreo, W. et. al. 2011 CALIFORNIA SINGLE-FAMILY WATER USE EFFICIENCY 

STUDY. July. Available at http://www.aquacraft.com/sites/default/files/pub/DeOreo-

%282011%29-California-Single-Family-Water-Use-Efficiency-Study.pdf 

Hendron, R. and J. Burch. 2007. Development of Standardized Domestic Hot Water Event 

Schedules for Residential Buildings. Presented at Energy Sustainability 2007 Long Beach, 

California. Jun 27–30. Conference Paper NREL/CP-550-40874. 

Hendron, R., J. Burch, M. Hoeschele, L. Ranier. 2009. “Potential for Energy Savings through 

Residential Hot Water Distribution Improvements.” Proceedings of the 3rd Annual International 

Conference on Energy Sustainability. Paper ES2009-90307. San Francisco, CA. 

Hendron, R., J. Burch, and G. Barker. 2010. Tool for Generating Realistic Residential Hot Water 

Event Schedules. Presented at SimBuild 2010 New York, New York. August 15–19. Conference 

Paper NREL/CP-550-47685. 

Hiller, C. 2005. Hot Water Distribution System Research – Phase I Final Report, California 

Energy Commission Report No. CEC-500-2005-161, May 2005. 

Hoeschele, M. and Chitwood, R. 2006. Field Survey Report: Documentation of Hot Water 

Distribution Systems in Sixty New California Production Homes, Davis Energy Group, Inc. and 

Chitwood Energy Management, Davis. 

Hoeschele, M. , E. Weitzel, J. McNeil, and D. Kosar. 2011. California Field Performance of 

Advanced Residential Gas Water Heating Technologies. Davis Energy Group, Inc. December 2.

Krigger, J. and Dorsi, C. 2009. Residential Energy: Cost Savings and Comfort for Existing 

Buildings. 5th Edition. Helena, MT: Saturn Resource Management Inc.; pp. 220. 

Larson, E. J. Froehlich, T. Campbell, C. Haggerty, L. Atlas, J. Fogarty and S. Patel. 2010. 

Disaggregated water sensing from a single, pressure-based sensor: An extended analysis of 

HydroSense using staged experiments. Pervasive and Mobile Computing. August. 

Lutz, J. 2005. “Estimating Energy and Water Losses in Residential Hot Water Distribution 

Systems.” Lawrence Berkeley National Laboratory. Paper LBNL-57199. Also ASHRAE 

Transactions 111 (2). 

Lutz, J. 2008. WATER HEATERS AND HOT WATER DISTRIBUTION SYSTEMS. Appendix 

Prepared by Lawrence Berkeley National Laboratory for the California Energy Commission, 

CEC-500-2005-007-APA. May. [this 473 page document includes several sub-reports from a 

large CEC project]

Lutz, J., G. Ghatikar, E. Edelson, S. Meyers. 2008. Hot Water Draw Patterns: Findings from 

Field Studies, APPENDIX H of CEC-500-2005-007-APA.
67 

Magnusson, L. 2009. “Methods and results for measuring hot water use at the fixture.” National 

Renewable Energy Lab. Presented at ACEEE June 2009 Hot Water Forum. 4B.

Maguire, J. M. Krarti, and X. Fang. 2011. An Analysis Model for Domestic Hot Water 

Distribution Systems. Presented at the 5th International Conference on Energy Sustainability and 

Fuel Cells Washington, D. C. August 7-10. Preprint NREL/CP-5500-51674. 

Mayer, P.W., W.B. DeOreo, E. Opitz, J. Kiefer, W. Davis, B. Dziegiefewski and J. Nelson. 

1999. Residential End Uses of Water. Report 99-41861. American Water Works Association 

Research Foundation.

RECS 2005, Residential Energy Consumption Survey. Table 13. www.eia.doe.gov/emeu/recs/. 

Springer, D., L. Ranier, M. Hoeschele and R. Scott. 2008. HWSIM: Development and Validation 

of a Residential Hot Water Distribution System Model. ACEEE Summer Study, pp. 1-267 to 1-

277. Asilomar, CA. August. 

Weihl, J.S. and Kempton, W. (1985). “Residential Hot Water Energy Analysis: Instruments and 

Algorithms.” Energy and Buildings, Vol. 8, pp. 197-204. 

A3.4 Literature and Articles Not Directly Cited

Chinery, G.T. 2006. Policy recommendations for the HERS Community to consider regarding 

HERS scoring credit due to enhanced effective energy factors of water heaters resulting from 

volumetric hot water savings due to conservation devices/strategies. Presented at meeting of 

EPA ENERGY STAR® for Homes. December.

Klein, G. 2006b. Saving Water and Energy in Residential Hot Water Distribution Systems. Slides 

from California Energy Commission at DOE website.

Klein, G. 2006c. “Saving Water and Energy in Residential Hot Water Distribution Systems.” 

Slides from California Energy Commission at DOE website.

Klein, G. 2008a. Structured Plumbing Offers Real Benefits. World Plumbing Review. Issue 1, 

pp. 38-40. 

Klein, G. 2008b. Design “Green” Hot Water Distribution Systems. PM Engineer. July.

Klein, G. and J. McCabe. 2010. THE FUTURE OF HOT WATER AND SOLAR THERMAL.

SOLAR 2010 Conference Proceedings. American Solar Energy Society.

Klein, G. 2011. Green Code and Hot Water System. Presented at ACEEE May 2011 Hot Water 

Forum. Berkeley, CA. 8B.
68 

Appendix B: Site Descriptions

Site #1 - Cazenovia, Ballina Rd - Group 3 (New WH and Distribution System)

Site 1 is a four-bedroom 2,800-ft2 house with an oil boiler. Hot water was originally provided by 

an indirect tank and oil fired boiler. The house dates to the late 1800s but was remodeled in 2000 

with new plumbing. The household has two full-time residents and three college-age adults who 

live there periodically. The relatively wet basement has a mix of original rubble foundation, new 

basement, old crawlspace, and new crawlspace. The proposed retrofit included installation of an 

HPWH and the addition of a recirculation pump and return line. 

Below is a list of events for Site 1:

• 11/15/12 – Data logger, thermocouples, switch closure CTs, and RH installed 

• 11/27/12 – Flow meter installed

• 11/28/12 – Flow meter wired to data logger

• 03/12/13 – Install HPWH - includes 1 new status (SRP) and 1 new temperature (TR) 

• 03/13/12 – 4th heating zone added to home (SZ4 added) 

• 04/03/13 – Install Recirculation Pump and Return line 

• 04/10/13 – Switch over to HPWH and Recirculation Pump 

• 06/12/13 – Added Dehumidifier Status and “Kill-A-Watt” style power meter for DH.

The new water heater and recirculation pump were purchased by CDH. The HPWH was 

purchased on sale at Lowe’s and the recirculation pump was purchased at a local plumbing 

supply shop. The plumbing contractor billed $900 (12 hours at $75/h) for labor and $78 for 

materials for the total install. We estimated that the HPWH installation accounts for 75% and the 

recirculation pump and return piping account for 25% of the total labor (see Table 29, Figure 45, 

Table 30, and Figure 46 through Figure 56).

Table 29. Cost Breakdown of Water Heater Install and Distribution Retrofit (Site 1) 

Equipment Costs

Item Labor (hrs) Material Installation Total Cost

Heat Pump Water Heater $ 1,078.92 9 $ 46.80 $ 675.00 1,800.72$ 

Recirculation Pump / Plumbing $ 219.00 3 $ 31.20 $ 225.00 $ 475.20

$ 1,297.92 12 78.00 $ $ 900.00 2,275.92$ 

Notes: CDH purchased the equipment directly. The Contractor provided material and labor 

at $75/hr labor. We estimated the labor and material breakdown associated with each item

Contractor Costs
69 

Figure 45. Site 1 pipe layout, pipe length, and sensor location

TF6

Thermistors (CR206)

Thermocouples (CR1000)

RH

TA1

TC

TT2 TT1

TT3

TA2 (crawl space)

TT4

TF1

TF2

TF3

TT5

TF5

TF4

TH

TR

TF7 TF8

Boiler

Indirect

Tank

HPWH

Recirculation

Pump

Expansion

Tank

Flow

Meter

Boiler DHW Shutoff

Master 

Bath Sink

Bathroom 

2 Sink

Bathroom 

2 Shower

Dishwasher

Kitchen 

Sink

1⁄2 Bath 

Sink

Utility 

Sink

Washing 

Machine

2nd Floor

1st Floor

1st Floor

1st Floor

26”

29.5”

68.5”

158”

24”

60”

110”

77”

30.5”

30”

50”

14.5”

7”

37.5”

149”

37”

24”

20.5”

Current Hot Water Pipe

Current Cold Water Pipe

Recirculation Loop Return Line

Front of House
70 

Table 30. Site 1 Data Point List and Descriptions

Logger Channel Type Name Description

Eng 

Units Sensor Notes

CR1000 A01 Analog TH Hot Water Outlet Temp °F Watlow type-T 1/16"

CR1000 A02 Analog TC Inlet Water Temp °F Watlow type-T 1/16"

CR1000 A03 Analog TA1 Space Temp near Unit °F Watlow type-T 1/16"

CR1000 A04 Analog TA2 Space Temp (crawl space) °F Watlow type-T 1/16"

CR1000 A05 Analog TT1 Trunk Temp - Master Bathroom °F Watlow type-T 1/16"

CR1000 A06 Analog TT2 Trunk Temp - Bathroom 2 °F Watlow type-T 1/16"

CR1000 A07 Analog TF1 Fixture Temp 1 - Dishwasher °F Watlow type-T 1/16"

CR1000 A08 Analog TF2 Fixture Temp 2 - Kitchen Sink °F Watlow type-T 1/16"

CR1000 A09 Analog TF3 Fixture Temp 3 - Sink (half bath) °F Watlow type-T 1/16"

CR1000 A10 Analog TF4 Fixture Temp 4 - Washing Machine °F Watlow type-T 1/16"

CR1000 A11 Analog TF5 Fixture Temp 5 - Utility Sink °F Watlow type-T 1/16"

CR1000 A12 Analog TT3 Trunk Temp 3 - Kitchen Trunk °F Watlow type-T 1/16"

CR1000 A13 Analog TT4 Trunk Temp 4 - Half Bath Trunk °F Watlow type-T 1/16"

CR1000 A14 Analog TT5 Trunk Temp 5 - Laundry Room Trunk °F Watlow type-T 1/16"

CR1000 A15 Analog TR Recirc Temp °F Watlow type-T 1/16" Installed 4/3/13

CR1000 A16 Analog RH Relative Humidity % Vaisala HMD60

CR1000 C1 SDM signal to SDM-SW8A

CR1000 C2 SDM signal to SDM-SW8A

CR1000 C3 SDM signal to SDM-SW8A

CR1000 C4 Status SDH Status Dehumidifier minutes Veris 800 Installed 6/11/13

CR1000 C5 Status SRP Status Recirc Pump minutes Veris 300 Installed 4/10/13

CR1000 C6 Status SE1 Element Status 1 minutes Veris 300 Installed 4/10/13

CR1000 C7 Status SE2 Element Status 2 minutes Veris 300 Installed 4/10/13

CR1000 C8 Pulse WE DHW Total Power kWh Wattnode Pulse Installed 4/10/13

CR1000 P1 Pulse FW Hot Water Use gal Omega FTB4605 1/2"

CR1000 P2 Pulse FC Condensate Flow gal tipping bucket not installed

Logger Channel Type Name Description

Eng 

Units Sensor Notes

CR206-1 A01 Analog TF6 Fixture Temp 6 - Master Bath Sink °F Minco Thermistor

Logger Channel Type Name Description

Eng 

Units Sensor Notes

CR206-2 A01 Analog TF7 Fixture Temp 7 - Bathroom 2 Sink °F Minco Thermistor

CR206-2 A02 Analog TF8 Fixture Temp 8 - Bathroom 2 Shower °F Minco Thermistor

Logger Channel Type Name Description

Eng 

Units Sensor Notes

SDM-SW8A IN 1 Status SC DHW Pump Status minutes Veris 300

SDM-SW8A IN 2

SDM-SW8A IN 3 Status SB Boiler Status minutes Veris 300

SDM-SW8A IN 4 Status SZ1 Status Zone 1 minutes Veris 300

SDM-SW8A IN 5 Status SZ2 Status Zone 2 minutes Veris 300

SDM-SW8A IN 6

SDM-SW8A IN 7 Status SZ3 Status Zone 3 minutes Veris 300

SDM-SW8A IN 8 Status SZ4 Status Zone 4 minutes Veris 300 Installed 3/13/13

BAD

BAD

Retrofit Points
71 

Site Photos

Figure 46. GeoSprings HPWH Figure 47. Bell & Gossett ecocirc recirculation pump 

installed on the return line to the domestic cold 

water inlet

Figure 48. 1⁄2 in. PEX was used for the recirculation return line with 1⁄2-in. copper used from the 

recirculation pump to the cold water tie-in

TH

TR

1⁄2-in. PEX 

Return Line

B&G 

Recirculation

Pump
72 

Figure 49. Return line from kitchen spur and half-bath 

sink with ball valve and check valve visible. This ball 

valve is almost completely closed allowing more 

recirculation from the kitchen spur than the 

main trunk.

Figure 50. Kitchen piping in crawl space with 

return line and kitchen sink branch visible. Ball 

valve at this location is fully open allowing for 

full recirculation when the pump is on.

Figure 51. Data logger enclosure with space 

temperature and relative humidity sensors 

installed on top

Figure 52. Cold water piping with flow meter 

and separate HPWH and boiler branches 

visible

1⁄2-in. PEX 

Return 

Line

From 

Kitchen 

Spur

Flow Meter

HPWH 

Cold 

Shutoff

To Boiler

To HPWH

RH

TA1

Kitchen 

Sink

1⁄2-in. PEX Return 

Line from 3⁄4” copper 

kitchen spur
73 

Figure 53. Boiler control board showing current 

switches measuring boiler zone statuses Figure 54. Dehumidifier in newer basement 

section with status and power being 

measured.

Figure 55. HPWH power is measured inside this 

enclosure. Inside are the CTs and power transducer.

Figure 56. Typical surface mount 

thermocouple installation. Thermal paste, 

thermocouple, foam insulation tape, and cable 

ties if necessary.
74 

Site #2—Syracuse, Gifford St Group 3 (New Water Heater and Distribution System)

Site 2 is a 11⁄2-story home with 3 bedrooms, 1 bathroom, and a full basement. According to the 

Onondaga County Department of Real Property, this house was built in 1920 and has 940 ft2. 

There are three ful- time occupants. This home originally had a standard 40-gal natural gas 

storage water heater from Bradford White (Model No.: MI403S6FBN4). The majority of the hot 

water plumbing is copper with the exception of one section in the basement that feeds the kitchen 

sink and clothes washer that is steel. All cold piping was originally steel. All steel plumbing was 

replaced with copper when on site for retrofit install of new water heater and recirculation pump 

with return line. An A.O. Smith Vertex GDHE 50 high efficiency condensing gas storage water 

heater and a Taco SmartPlus recirculation pump were installed on 5/21/2013. 

Below is a list of events for Site 2:

• 12/12/12 – Data logger and thermocouples installed 

• 12/14/12 – Flow meter installed and wired to data logger

• 05/20/13 – Added QU calculation to program 

• 05/21/13 – Installed new water heater, recirculation pump, SDHW, SRP, TR, FG, and 

TAO

Table 31. Cost Breakdown of Water Heater Install and Distribution Retrofit (Site 2) 

The city-licensed plumbing contractor provided a not-to-exceed quote of $4,778 with a material 

and labor costs breakdown. CDH purchased the recirculation pump at a local plumbing supply 

shop. The contractor was observed to be on site for a total of 12 hours and we assumed the new 

water heater installation accounts for 5 hours of this time. We allocated 4 hours to the new cold 

water piping and 3 hours to installing the recirculation pump. The AO Smith GDHE-50 water 

heater was estimated to be $2,106 with sales tax (retail price). This left $1,445 for miscellaneous 

materials, which we allocated across the three items.

Equipment Costs

Retrofit Item Labor (hrs) Material Installation Total Cost

$ 2,106.00 5 $ 433.50 $ 511.25 $ 3,050.75

New Cold Water 4 $ 722.50 $ 409.00 $ 1,131.50

$ 392.00 3 $ 289.00 $ 306.75 $ 987.75

Total: $ 2,498.00 12 1,445.00$ $ 1,227.00 $ 5,170.00

Notes: Total plumber costs were $4,778. CDH purchased pump directly. Water heater cost estimated by CDH. 

Total labor hours based on observed field time. Allocation of labor and material to each item estimated by CDH

Contractor Costs

HE Gas Condensing Storage Water Heater

Recirculation Pump and Plumbing
75 

Figure 57. Site 2 floor plan

Dining Room

Bathroom

sink

tub 

shower

Kitchen

Living room

CW sink
76 

TA2

TR

Washing

Machine

Front of House

Return Line

Old 

Water 

Heater

New 

Condensing 

Storage 

Water 

Heater

TF1

TF2

TF4 TF3

TH TC

FW

FG

TT1

TT2

TA1

SDHW

Recirculation

Pump

SRP

Kitchen 

Sink Bathroom 

Sink

Bathroom 

Shower

1st Floor 1st Floor

 

Figure 58. Site 2 pipe layout and sensor location
77 

Table 32. Site 2 Data Point List and Descriptions

Logger Channel Type Name Description

Eng 

Units Sensor Notes

CR1000 A01 Analog TH Hot Water Outlet Temp °F Watlow type-T 1/16"

CR1000 A02 Analog TC Inlet Water Temp °F Watlow type-T 1/16"

CR1000 A03 Analog TFG Temp Flue Gas °F Watlow type-T 1/16" Removed during retrofit 5/21/13

CR1000 A04 Analog TA1 Space Temp near Unit °F Watlow type-T 1/16"

CR1000 A05 Analog TA2 Space Temp near Piping °F Watlow type-T 1/16"

CR1000 A06 Analog TT1 Trunk Temp - Bathroom °F Watlow type-T 1/16"

CR1000 A07 Analog TT2 Trunk Temp - Kitchen °F Watlow type-T 1/16"

CR1000 A08 Analog TF1 Fixture Temp 1 - Bathroom Sink °F Watlow type-T 1/16"

CR1000 A09 Analog TF2 Fixture Temp 2 - Bathroom Shower °F Watlow type-T 1/16"

CR1000 A10 Analog TF3 Fixture Temp 3 - Kitchen Sink °F Watlow type-T 1/16"

CR1000 A11 Analog TF4 Fixture Temp 4 - Washing Machine °F Watlow type-T 1/16"

CR1000 A12 Analog TR Recirc Temp °F Watlow type-T 1/16" Installed during retrofit 5/21/13

CR1000 C1 Status SRP Status Recirc Pump minutes Veris 300 Installed during retrofit 5/21/13

CR1000 C2 Status SDHW DHW Status minutes Veris 300 Installed during retrofit 5/21/13

CR1000 P1 Pulse FW Hot Water Use gal Omega FTB4605 1/2"

CR1000 P2 Pulse FG Unit Gas Use cf Domestic Meter Pulser Installed during retrofit 5/21/13

Retrofit Points
78 

Site Photos

Figure 59. Original standard gas storage water heater

Figure 60. New condensing gas storage water 

heater installed during retrofit.

Figure 61. IMAC gas meter with pulser to 

measure gas use.

TF1

TT2 TF2
79 

Figure 62. Taco SmartPlus recirculation pump installed on hot water supply 

with remote temperature sensor

Figure 63. Flow meter and cold water 

temperature after retrofit Figure 64. Current switch used to measure water 

heater status

Site #3 - Manlius, Brickyard Falls Rd - Group 2 (New Tankless)

Site 3 is a raised ranch with three bedrooms and two baths. This house was built in 1976 and has 

remained unchanged since built. Hot water was originally provided by a Bradford White 40-gal 

natural gas storage water heater. The kitchen and two baths are on the second level. The 

laundry/utility room is on the first level. All plumbing is copper with 3⁄4-in. to 1⁄2-in. transitions.

All but the bathroom 2 sink fixture branches are accessible. A Rinnai non-condensing tankless 

water heater was installed on March 22, 2013. Distribution changes were required to relocate the 

water heater and provide direct-vent capability. The changes can be seen in the pipe schematic 

figure below. 

Below is a list of events for Site 3: 

• 11/27/12 – Flow meter installed

Recirculation 

Pump

Remote Temp 

Sensor

Flow Meter

TC

SDHW
80 

• 12/12/12 – Data logger and Wi-Fi bridge setup and installed 

• 12/13/12 – Thermocouples installed and wired (except for bathroom 2 TCs) and flow 

• 12/18/12 – Changed program to expand range of thermocouple for flue gas temperature 

• 12/21/12 – Installed Bathroom 2 shower thermocouple around 6:00 p.m. 

• 03/22/13 – New tankless water heater installed

• 04/13/13 – QU calculation added to program

Table 33. Cost Breakdown of Water Heater Installation (Site 3) 

The tankless water heater was provided and installed by the contractor for fixed price of $2,420. 

We allocated $1,220 to the equipment and $200 to other miscellaneous materials. The hours 

were inferred based on the $75/h rate charged by this contractor at other sites. The installation 

was completed in 1 day by two plumbers.

Equipment Labor (hrs) Material Installation Total Cost

Tankless Water Heater $ 1,220 13 200 $ $ 1,000 $ 2,420

Item

Contractor Costs
81 

TT4

17” 9”

Kitchen 

Sink

Bathroom 2

Sink

Bathroom 2 

Shower

Master Bath 

Shower

Master Bath

Sink

Washing 

Machine

Laundry

Sink

Flow

Meter

TF5

TF6

TF4

TF2

TT3

TT1

TF1

TF7

TF8

TH

TC

Tankless

Water 

Heater

Old

Water 

Heater

2nd Level

2nd Level 2nd Level

Current Hot Water Pipe

Current Cold Water Pipe

Old Hot Water Pipe

17.5”

7” 52.5”

13” 24”

41.5”

8.5”

2.5”

74”

62.5”

~60”

39”

12.5”

15”

10”

~12” ~12”

~48”

9.5”

3”

12”

41.5”

9”

Dishwasher

Front of House

TA1

SDHW FG

Figure 65. Site 3 pipe layout and sensor location
82 

Bathroom

Living Room

Master Bedroom

Guest Bedroom

Master Bath

Dining Room

Garage

Utility

Family Room

Kitchen

DW KS

Shower 2

CW US

S2

S1

Shower 1

Office/Bedroom 3

WH

Figure 66. Site 3 floor plan

First Level

Second Level
83 

Table 34. Site 3 Data Point List and Descriptions

Logger Channel Type Name Description

Eng 

Units Sensor Notes

CR1000 A01 Analog TH Hot Water Outlet Temp °F Watlow type-T 1/16"

CR1000 A02 Analog TC Inlet Water Temp °F Watlow type-T 1/16"

CR1000 A03 Analog TFG Temp Flue Gas °F Watlow type-T 1/16" Removed during retrofit 3/22/13

CR1000 A04 Analog TA1 Space Temp near Unit °F Watlow type-T 1/16"

CR1000 A05 Analog TT1 Trunk Temp - Bathrooms °F Watlow type-T 1/16"

CR1000 A06 Analog

CR1000 A07 Analog TT3 Trunk Temp - Kitchen °F Watlow type-T 1/16"

CR1000 A08 Analog TT4 Trunk Temp - Laundry °F Watlow type-T 1/16"

CR1000 A09 Analog TF1 Fixture Temp 1 - Master Bath Sink °F Watlow type-T 1/16"

CR1000 A10 Analog TF2 Fixture Temp 2 - Master Bath Shower °F Watlow type-T 1/16"

CR1000 A11 Analog

CR1000 A12 Analog TF4 Fixture Temp 4 - Bathroom 2 Shower °F Watlow type-T 1/16"

CR1000 A13 Analog TF5 Fixture Temp 5 - Kitchen Sink °F Watlow type-T 1/16"

CR1000 A14 Analog TF6 Fixture Temp 6 - Dishwasher °F Watlow type-T 1/16"

CR1000 A15 Analog TF7 Fixture Temp 7 - Washing Machine °F Watlow type-T 1/16"

CR1000 A16 Analog TF8 Fixture Temp 8 - Laundry Sink °F Watlow type-T 1/16"

CR1000 C8 Status SDHW DHW Status minutes Veris 300 Installed during retrofit 3/22/13

CR1000 P1 Pulse FW Hot Water Use gal Omega FTB4605 1/2"

CR1000 P2 Pulse FG Unit Gas Use cf Domestic Meter Pulser Installed during retrofit 3/22/13

OPEN

OPEN

Retrofit Points
84 

Site Photos

Figure 67. Original storage water heater 

location

Figure 68. New tankless water heater from 

retrofit

Figure 69. IMAC gas meter with pulser Figure 70. Flow meter and laundry trunk 

Flow Meter

TT4

Cold Water 

Supply for Old 

Water Heater

TH
85 

temperature.

Figure 71. Showing direction of hot water flow 

from tankless water heater

Figure 72. Shows direction of hot water flow 

after retrofit. The old hot water supply tied into 

the pipe at the elbow circled in red and was a 

vertical drop to the old water heater.

Figure 73. Shows lengthened 

cold water supply piping

From Tankless 

Water Heater

From Tankless 

Water Heater

To Laundry 

and Kitchen 

Fixtures

To Bathroom 

Fixtures

To Water 

Heater

To Laundry 

and Kitchen 

Fixtures

Old Hot Water

Supply Tie In
86 

Site #4 – Cazenovia, Burton St - Group 1 (Baseline)

Site 4 was built in 1860 and extensively renovated in 2010. A Rinnai tankless water heater and 

manifold water distribution with PEX plumbing was installed during the renovation. The old 

standard gas water heater was kept to provide hot water to a full bathroom on the second floor 

and a half bathroom on the first floor. All piping is copper. The Rinnai tankless water heater 

provides hot water for the master bathroom on the second floor, kitchen, and laundry room. 

No changes were made to this DHW system. 

Old Water 

Heater New Water 

Heater

Figure 74. Site 4 floor plan
87 

Figure 75. Site 4 Pipe Layout 

TH TC

TA

TF5

Thermocouples 

Thermistors 

TC

TH

TF6

TT7

TF2

TF1

FW

FW2

SDH

TF

TA

1⁄2 

Bath 

Sink

Old Bath Sink

Utility 

Sink

Old Water 

Heater

Renovated Side with Rinnai 

Tankless Water Heater

Distribution 

Manifold

Front of House

Front of 

House

TF3

TF4

1st Floor

1st

2nd

Floor

Cold 

Supply

Original Basement Side and 

Old Water Heater
88 

Table 35. Site 4 Data Point List and Descriptions

Logger Channel Type Name Description

Eng 

Units Sensor Notes

CR1000 A01 Analog TH Tankless Hot Water Outlet Temp °F Watlow type-T 1/16"

CR1000 A02 Analog TC Tankless Inlet Water Temp °F Watlow type-T 1/16"

CR1000 A03 Analog TFG Tankless Flue Gas Temp °F Watlow type-T 1/16"

CR1000 A04 Analog TA Space Temp near Tankless °F Watlow type-T 1/16"

CR1000 A05 Analog TF1 Fixture Temp 1 - Master Bath Sink °F Watlow type-T 1/16"

CR1000 A06 Analog TF2 Fixture Temp 2 - Clothes Washer °F Watlow type-T 1/16"

CR1000 A07 Analog TF3 Fixture Temp 3 - Kitchen Sink °F Watlow type-T 1/16"

CR1000 A08 Analog TF4 Fixture Temp 4 - Laundry Sink °F Watlow type-T 1/16"

CR1000 A09 Analog TF5 Fixture Temp 5 - Master Bath Shower°F Watlow type-T 1/16"

CR1000 C8 Pulse SDHW Tankless Status min Veris CT

CR1000 P1 Pulse FW Tankless Hot Water Use gal Omega FTB4605 1/2" 151.4 pulse/gal mult. = 0.00660502

Logger Channel Type Name Description

Eng 

Units Sensor Notes

CR206-1 A01 Analog TH2 Old Heater Hot Water Outlet Temp °F Minco Thermistor

CR206-1 A02 Analog TC2 Old Heater Inlet Water Temp °F Minco Thermistor

CR206-1 A03 Analog TF6 Fixture Temp 6 - Utility Sink °F Minco Thermistor

CR206-1 A04 Analog TA2 Space Temp near Old Heater °F Minco Thermistor

CR206-1 A05 Analog TT7 Trunk Temp 7 - Old Bathroom °F Minco Thermistor

CR206-1 P-SW Pulse FW2 Old Heater Hot Water Use gal Omega FTB4605 1/2" 151.4 pulse/gal mult. = 0.00660502

Logger Channel Type Name Description

Eng 

Units Sensor Notes

CR206-2 A01 Analog TF7 Fixture Temp 7 - Old Bathroom Sink °F Minco Thermistor
89 

Site #5 – Syracuse, Hornady Dr - Group 1 (Baseline)

Site 5 is a split level home with three bedrooms and two baths and is occupied by two adults with 

a baby due in June 2013. According to the Onondaga County Department of Real Property this 

house was originally built in 1989 and has 1,640 ft2

. Hot water is provided by a 40 gal General 

Electric SmartWater natural gas storage water heater (Model No.: PG40S09AVJ00) with a 

manufacturing date of December 2006. There is a bathroom on the top level, a bathroom on the 

middle level and a laundry room on the lowest level. All plumbing is copper with all but the 

kitchen fixtures reachable from the lowest level.

No changes were made to this DHW system. 

Bathroom

sink

tub 

shower

Dining Rm

Living room

sink

Laundry

Kitchen

DW

CW sink shower sink

Upper Levels

Lower Levels

Figure 76. Site 5 Floor Plan
90 

Figure 77. Site 5 Pipe Layout and Sensor Location

Thermistors (CR206)

Thermocouples (CR1000)

TF8

TA

1

TH

TF

G

TC

TF3

TF4

TT1

TT4

TT2

TA TF5

1

TA

1

TA

1

TT3

TF7

Front of 

House

Upper 

Level

Lower 

Level
91 

Table 36. Site 5 Data Point List and Descriptions

Logger Channel Type Name Description

Eng 

Units Sensor Notes

CR1000 A01 Analog TH Hot Water Outlet Temp °F Watlow type-T 1/16"

CR1000 A02 Analog TC Inlet Water Temp °F Watlow type-T 1/16"

CR1000 A03 Analog TFG Temp Flue Gas °F Watlow type-T 1/16"

CR1000 A04 Analog TA1 Space Temp near Unit °F Watlow type-T 1/16"

CR1000 A05 Analog TA2 Space Temp near Piping °F Watlow type-T 1/16"

CR1000 A06 Analog TT1 Trunk Temp - Laundry °F Watlow type-T 1/16" Washing Machine

CR1000 A07 Analog TT2 Trunk Temp - Bathroom °F Watlow type-T 1/16" Bathrooms

CR1000 A08 Analog TT3 Trunk Temp - Upper Bath °F Watlow type-T 1/16" Upper Bath

CR1000 A09 Analog TT4 Trunk Temp - Kitchen °F Watlow type-T 1/16" Kitchen

CR1000 A10 Analog TF1 Fixture Temp 1 °F Watlow type-T 1/16" Lower Bathroom Sink

CR1000 A11 Analog TF2 Fixture Temp 2 °F Watlow type-T 1/16" Lower Bathroom Shower

CR1000 A12 Analog TF3 Fixture Temp 3 °F Watlow type-T 1/16" Washing Machine

CR1000 A13 Analog TF4 Fixture Temp 4 °F Watlow type-T 1/16" Laundry Sink

CR1000 A14 Analog TF5 Fixture Temp 5 °F Watlow type-T 1/16" Upper Bathroom Sink

CR1000 A15 Analog TF6 Fixture Temp 6 °F Watlow type-T 1/16" Upper Bathroom Shower

CR1000 P1 Pulse FW Hot Water Use gal Omega FTB4605 1/2" 151.4 pulse/gal mult. = 0.00660502

Logger Channel Type Name Description

Eng 

Units Sensor Notes

CR206 A01 Analog TF7 Fixture Temp 7 °F Minco Thermistor Kitchen Sink

CR206 A02 Analog TF8 Fixture Temp 8 °F Minco Thermistor Dishwasher
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