Hot Water Improvements Top Warm Climate Weatherization Measures
 
Hot Water Improvements Top Warm Climate Weatherization MeasuresLow-flow showerheads got the highest savings-to-investment rating in the study, but that category was given a low confidence rating. More studies are needed.Reducing hot water costs is the most cost-effective way to save money for low-income housing in warm climates. This is one conclusion that can be drawn from a new study on the cost-effectiveness of energy-saving measures for low-income housing in warm climates. The study brings together the findings of existing reports in order to estimate the cost-effectiveness of various low-income weatherization measures.

Energy conservation measures for warm climates may differ from those for cold climates because they must not only reduce conduction of heat between the outside and the inside of the house, but also reduce the effects of the sun. In cold weather, the heat from the sun helps cut energy costs, but in hot climates, it adds to the cooling bill.

The researchers from , Mike Gettings and Michaela Martin, examined eight categories of warm-climate energy-saving measures: cooling and heating equipment, hot water, insulation, ventilation and infiltration, lighting, solar load, window and door replacement, and appliances. The comprehensive chart (see ) cites the average first-year savings, installation cost, savings-to-investment ratio (SIR), and maintenance requirements for each measure. The study also examines how sensitive each measure is to customer interactions, customer education, climate, building characteristics, and number of occupants. Confidence level ratings in the report reflect the degree of certainty, quality, and variability of information used to determine the SIRs, as seen in the literature.

Measures that reduced hot water use got the highest SIR rankings, mainly because of their universal application in all climates and their relatively low cost. Hot water accounts for 20%D40% of the energy consumed by low-income homes in warm weather climates. Most of the 18 water heating measures that were examined are well established as techniques for reducing water-heating energy consumption. Installation of water tank insulation and flow restrictors in homes with electric water heaters saved the most money compared to the installation cost. Tank insulation can be installed for about $25, and it saved from $10 to $38 per year. Low-flow showerheads cost only $30 and saved $27 per year. Other high-SIR measures in the hot-water category included heat traps on electric hot water tanks, gas-fired water heater tank insulation, and temperature setbacks on electric water heaters. On electric tanks, heat traps saved $17 per year and cost about $30 to install. Insulating gas-fired tanks saved from $3 to $10 per year and cost about $25. Depending on the existing water heater temperature setting, reducing the setting cost virtually nothing yet saved from $10 to $17 for electric water heaters. The finding that water-heater efficiency improvements save the most money compared to installation costs supports what is commonly practiced in the field.

On the other end of the SIR rating scale, one of the lowest-ranking measures was forced attic ventilation using a solar powered fan. Savings were small ($2D$3 per year), while the measure cost $800 to implement. Other low-ranking measures included foundation insulation for slab-on-grade (a measure that is far more cost-effective in cold-climates), gas tankless water heaters, reflective roofing in already insulated attics, and refrigerator tune-up (unless performed by the homeowner). Several envelope measures ranked low, but they were examined for their effects on cooling only. They would be more effective in climates with significant heating requirements. These measures included adding wall insulation and increasing the attic insulation level from R-19 to R-30.

Russell Clark, who works in low-income weatherization with the Department of Commerce Energy Office in Arizona, says he will use the report's findings to compare costs of weatherization measures done in states where cooling measures are more important. "Costs are an obviously sensitive parameter and can significantly change the SIR value," says Clark.

Review of Water, Lighting, and Cooling Energy Efficiency Measures for Low-Income Homes Located in Warm Climates is available to the public from the National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Road, Springfield VA 22161.

-Deborah Rider Allen

Deborah Rider Allen is a freelance writer in Richmond, Virginia.

Publication of this article was supported by the U.S. Department of Energy's Office of State and Community Programs, Energy Efficiency and Renewable Energy.

Weatherization Measures with High Confidence Ratings

Measure
1st year savings (kWh or Mbtu)
1st year savings ($)
Installation Cost ($)
SIR (*=cooling only)

Electric Hot Water Measures

Heat traps on tank
210 kWh
$17
$30
5.7

Tank insulation
130D480 kWh
$10D$38
$25
4D15

Temperature setback
130D210 kWh
$10D$17
$0
High

Electric tankless water heater
320D790 kWh
$25D$63
$800
0.32D0.8

Small solar water heater
2,000 kWh
$170
$1,100
2.2

Large solar water heater
1,800D3,000 kWh
$140D$240
$2,500
0.79D1.3

Gas Hot Water Measures

Heat traps on tank
0.72 Mbtu
$5
$30
0.57

Tank insulation
0.43D1.6 Mbtu
$3D$10
$25
1.4D4.6

Temperature setback
0.43D0.72 Mbtu
$3D$4
$0
High

Gas tankless water heater
1.1D2.7 Mbtu
$7D$17
$1,174
0.07D0.17

Cooling and Heating Equipment Measures

Air conditioner tune-up
90D790 kWh
$7D$64
$80
0.20D1.4*

Window air conditioner replacement
100D890 kWh
$8D$71
$600
0.15D1.3*

Central air-conditioner replacement
100D890 kWh
$8D$71
$1,500
0.06D0.77*

Evaporative cooler installation
960 kWh
$77
$1,000
0.72*

Duct sealing
60D500 kWh
$4D$40
$200
0.16D1.63*

Lighting Measures

Replacement of 5 or 6 lamps
220D320 kWh
$18D$26
$90D$110
1.2D1.4

Insulation Measures

Add attic insulation (R-19 to R-30)
40D110 kWh
$3D$9
$400
0.12D0.33*

Foundation insulation (basement)
190 kWh
$15
$640
0.38*

Foundation insulation (crawl space)
200 kWh
$16
$600
0.45

Foundation insulation (slab-on-grade)
70D240 kWh
$5D$20
$1,700
0.05D0.19

Wall insulation in wood frame walls with attic insulation
35D360 kWh
$3D$29
$1,200
0.04D0.40*

Wall insulation of masonry walls with attic insulation
35D360 kWh
$3D$29
$4,900
0D0.09*

Ventilation Measures

Passive attic ventilation
10D85 kWh
$1D$6
$50
0.22D1.4

Mechanical solar-powered attic ventilation
2D170 kWh
$2D$13
$800
0.02D0.13

Skirting of mobile homes heated by gas or heat pumps
24D480 kWh
$1D$39
$300
0.03D0.77

Skirting mobile homes heated by electric resistance heat
45D920 kWh
$4D$73
$300
0.07D1.47

Whole-house fan installation
50D330 kWh
$4D$26
$200
0.17D1.1

Solar Load Reduction Measures

Full-year solar screens and films

$0D$10 per unit
$37 per unit
0D2.0

Summer-only solar screens and films

$4D$10 per unit
$37 per unit
0.6D2.2

Radiant barriers with R-11 attic insulation
not available
not available
$360
0.51D0.86

Radiant barriers with R-30 attic insulation
not available
not available
$360
0.15D0.31

Awnings

$2D$37
$90 per unit
0D0.7

The U.S. Department of Energy recently collected extensive information on the cost-effectiveness of various efficiency measures for low-income homes in warm climates. This table shows some of the findings that were given high confidence ratings. The most reliable savings arise from measures that reduce water-heating energy use.