Bob Hemphill, Consultant (for Peter Mayer)

Residential Hot Water
Consumption Trends
Peter Mayer
Vice President and Project Engineer
2709 Pine St.
Boulder, CO 80302
www.aquacraft.com
1

Residential Hot Water Research
• Important area of research with limited
current data available
• Hot water is 2nd largest portion of
residential energy consumption in US
• 2 EPA studies (2000 - 2003) conducted by
Aquacraft
• Forthcoming ASHRAE Research Project
establishing “protocol” for residential hot
water demand measurements

Crosscutting Trends
• Is residential hot water use likely to change?
– YES…BUT it could go up or down
• Trends favoring decrease
– Efficient plumbing fixtures and appliances
• Trends favoring increase
– Changes in home building practices, larger bath
tubs, new devices that use hot water

EPA/Aquacraft Hot Water Research
• 2 study sites - Seattle, WA and East Bay
Municipal Utility District (Greater Oakland,
CA)
• Hot water demand research part of water
efficient product retrofit studies
• 10 homes were studies in each study site.
Overall, n=20.

Research Methodology
• Study group selection (modified random sample)
• Site audits
• Installation of water meter on in-flow to hot
water heater
• Flow data loggers installed on main meter and
hot water meter
• 2-weeks of baseline flow data (10-second
intervals) prior to retrofits
• 4-weeks of post-retrofit flow data

Meter-Master Flow Data Recorder

Data Analysis Methods
• Flow trace data were analyzed using Trace
Wizard © water use analysis software
• Water used for each specific end use was
determined
• Paired t-test analyses were used to evaluate the
demands for each end use measured at the study
homes in the pre and post-retrofit periods

Trace Wizard Water Use Analysis Tool
Main meter flow trace
Hot water meter flow trace

Residential Water Use - Baseline
Hot water
40%
(25.1 gcd)
Hot water
30%
(21.1 gcd)
Cold water
60%
(37.1 gcd)
Average Daily Per Capita Use - Baseline = 62.2 gcd
Cold water
70%
(49.8 gcd)
Average Daily Per Capita Use - Baseline = 70.9 gcd
Seattle, Washington
Oakland, California

Baseline Hot Water Use - By End Use
Seattle
Oakland
Hot (gcd) Cold (gcd) Hot (gcd) Cold (gcd)
Bath 4.2 5.3 1.7 1.9
Clothes washer 3.9 14.1 1.9 12.4
Dishwasher 0.9 0.9 1.4 1.4
Faucet 8.6 11.9 8.6 13.2
Leak 1.2 4.4 0.7 11.2
Shower 6.3 8.7 6.9 9.6
Other 0.01 0.02 0.02 0.03
TOTAL 25.1 62.2 21.1 70.9

Retrofit of Efficient Fixtures and
Appliances

Post-Retrofit Hot Water Use
Seattle
Oakland
Baseline
(gcd)
Post-Retrofit
(gcd)
Baseline
(gcd)
Post-Retrofit
(gcd)
Bath 4.2 2.5 1.7 1.5
Clothes w a sher 3.9 1.5 1.9 1
Dishw a sher 0.9 1 1.4 1
Faucet 8.6 7.7 8.6 6.2
Leak 1.2 0.8 0.7 0.7
Shower 6.3 7 6.9 6
Other 0.01 0.01 0.02 0.01
TOTAL 25.1 20.5 21.1 16.5

ASHRAE Research
• American Society of Heating, Refrigerating and Air-
Conditioning Engineers
• Metering Residential Hot Water by End-Use -
Development of Standard Protocol
• Dept. of Architecture, University of Nebraska, Lincoln
• Developed complex field protocol including temperature
and water use monitoring
• Simpler, less expensive data collection approach may be
desirable
• Limited data collection effort - researchers hope to expand
effort in near future

Trends Suggesting Increasing
HW Demand - 1
Floor Area of New Privately Owned Single Family
Dwellings by Year of Construction
Source: US Census Bureau

Trends Suggesting Increasing
HW Demand - 2
• Increasing number of stories per house
• Increasing number of bathrooms per house
• Increase floor area per house
• Jacuzzi tubs and other new fixtures

Conclusions
• Cross-cutting trends in residential hot water
use exist
• Plumbing codes and efficient fixtures likely
to decrease HW demand in older housing
stock
• Building trends in new houses suggests
potential for increased demand
• Important area for future research

For more information…..
www.aquacraft.com - download reports, demo
software, etc.
mayer@aquacraft.com
2709 Pine St.
Boulder, CO 80302
303-786-9691
303-786-8337 (fax)