by Harvey Sachs, 09/04/06
Harvey M. Sachs, Ph.D., directs the Buildings Program at the American Council for an Energy-Efficient Economy (ACEEE). He works on building codes, equipment standards, and market transformation to increase the use of better products and practices. His research focuses on emerging technologies and practices. Before joining ACEEE, he was policy director of the Center for Global Change at the University of Maryland. Sachs has also served as assistant commissioner for energy in the New Jersey Department of Commerce, Energy, and Economic Development and as technical director of the Geothermal Heat Pump Consortium.
The house is a system. You save money and improve performance when you take cost-effective measures that reduce building loads, and then install systems and appliances that are the right size to meet the reduced loads. In general, oversizing worsens performance and increases costs.
The most effective strategy for improving household energy efficiency is to first target your home’s envelope—walls, attic, windows, and doors. Then reduce the energy consumption of systems, such as heating, cooling, lighting and appliances. Finally, consider clean energy generation (solar, geothermal, and so on).
1. Make sure your walls and attic are well insulated.
Effective insulation slows the rate that heat flows out of the house in winter or into the house in summer, so less energy is required to heat or cool the house. If your house has no wall insulation, and it has more-or-less continuous wall cavities (such as conventional stud walls), blown-in insulation can greatly improve your comfort and save enough energy to be very cost-effective. (It rarely pays to blow additional insulation into already insulated walls.) If your attic is unfinished, it often pays to upgrade its insulation.
Your contractor’s expertise is more important than the insulation material you choose. Properly installed fiberglass, cellulose and most foam insulation materials vary little in their R-value (a rating of a material’s resistance to heat flow) or the heat conduction of the completed wall system. The key is “properly installed.” Ideally, the contractor will use an infrared camera during or after installation to look for voids.
2. Upgrade or replace windows.
If your windows are old and leaky, it may be time to replace them with energy-efficient models or boost their efficiency with weatherstripping and storm windows. It is almost never cost-effective to replace windows just to save energy: in most houses, windows account for less than 15 percent of the heat loss, so even if you replaced all the windows with perfect insulators, you would save at most 15 percent. But if you are replacing windows for other reasons, in many areas the cost of upgrading to Energy Star–rated windows is very modest, perhaps $15 per window. This upgrade would be cost-effective—and increase your comfort to boot.
3. Plant shade trees and shrubs around your house.
If your house is older, with relatively poor insulation and windows, good landscaping (particularly deciduous trees) can save energy, especially if planted on the house’s west side. In summer, the foliage blocks infrared radiation that would warm the house, while in winter the bare branches let this radiation come through. Of course, if your house has very good insulation and Energy Star or better windows, the effect is much, much smaller because the building shell itself is already blocking almost all the heat gain.
4. Replace an older furnace with a high-efficiency system.
If your furnace was built before 1992 and has a standing pilot, it probably wastes 35 percent of the fuel it uses, and it may be near the end of its service life. In this case, in climates with at least 4,500 to 5,000 heating degree days, ACEEE recommends early replacement with a condensing furnace with annual efficiency of at least 90 percent. This type of furnace wastes no more than 10 percent of the natural gas you buy, and may save you as much as 27 percent on your heating bill.
If your furnace was installed after 1991, it probably has an annual fuel utilization efficiency (AFUE) rating of 80 percent, so the savings from replacement is smaller, but would be at least 11 percent if the unit is working perfectly. Your heating service technician or energy auditor may be able to help you determine the AFUE of your present system.
5. Improve the efficiency of your hot water system.
First, turn down the temperature of your water heater to the warm setting (120°F), particularly for fossil-fuel water heaters with their high standby losses. Second, insulate your hot water lines so they don’t cool off as quickly between uses. Third, use low-flow fixtures for showers and baths. While storage water heater standards were raised in 2001, it was probably not enough to justify throwing out an existing water heater that is working well.
Advanced contractors are now installing “on demand” hot water circulating loops that use a small pump to accelerate delivery of hot water to remote fixtures, which works great with low-flow fixtures. These are activated when users turn on a bathroom or kitchen tap, and turn off when hot water reaches the fixture. In ACEEE’s opinion, a continuous recirculating “hotel” loop wastes enormous amounts of water heating energy, and electricity for pumping.
6. Replace incandescent lights with compact fluorescent lamps (CFLs).
CFLs can save three-quarters of the electricity used by incandescents. Most people don’t think about the fact that the electricity to run a lightbulb costs much more than the bulb itself. One of the new CFLs costs about $3, but it lasts 10,000 hours and uses only about 27 watts to generate as much light as a 100-watt incandescent bulb. During its life, it uses about $22 in electricity, so the total cost is about $25. A 100-watt incandescent bulb costs 50 cents, but lasts 1,000 hours so you need 10 of them ($5 to buy) to last 10,000 hours. In those 10,000 hours you will use 1,000 kilowatts of electricity, which will cost more than $80 at a national average price. So the lighting cost of the CFL is less than one-third of the cost for the incandescent. The best targets for replacement are are 60- to 100-watt bulbs used several hours a day, because usage affects how long it takes to recover the investment.
7. If you are thinking of buying a new refrigerator, don’t leave the old one plugged in, in the basement, as a backup for party supplies and liquid refreshment.
Electricity to operate the old one isn’t free: figure an extra $50-150 per year to run it. In contrast, the new one, particularly if Energy Star rated, may cost only $30-60 per year to run because refrigerator efficiency has improved so much in the past three decades. Under these circumstances, think about how much refrigeration you really need. The best rule is to have only one refrigerator, and to size it to meet your real needs. That allows the luxury of ice-makers and similar conveniences with a clear conscience.
8. Take advantage of new tax incentives to improve your home.
The 2005 Federal Energy Bill offers tax credits for exemplary residential efficiency purchases in 2006 and 2007. For existing houses, the available credits are 10 percent of the improvement cost (the tax rebate is capped at $500 total, with smaller caps for certain improvements) for many measures, including: insulation and envelope improvements meeting International Code Council (ICC) specifications; windows meeting ICC specifications; central air conditioners or heat pumps meeting 2006 Consortium for Energy Efficiency specifications; furnaces and boilers with AFUE of 95 or better; water heaters with Energy Factor of .80 or better; heat pump water heaters with an Energy Factor of 2.0 or better; and ground source heat pumps meeting specified performance levels.
9. Schedule an energy audit for more expert advice on your home as a whole.
Energy auditors and raters use specialized tools and skills to evaluate your home and recommend the most cost-effective measures to improve its comfort and efficiency, as well as the best sequence for doing them to take advantage of interactions. The rater can also provide independent verification of contractors’ work quality. Look for raters who are
RESNET Accredited. In some regions, there are Home Performance with Energy Star programs, too. Most of these programs include low-cost home assessment and strong quality assurance practices and/or inspections.
