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, over-sizing 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 improve the energy efficiency 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.
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Your contractor’s expertise is more important than the insulation material you choose. Properly installed fiberglass, cellulose, and most foam insulation materials can all reduce 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. According to EnergyStar.gov, replacing windows will save 7 to 24 percent of your heating and air-conditioning bills, but the larger savings would be associated with replacing single-glazed windows. However, if you are replacing windows for other reasons anyway, in many areas the additional cost of Energy Star–rated replacement 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 Furnace
If your furnace was built before 1992 and has a standing pilot, it probably wastes 35 percent of the fuel it uses, and it is probably near the end of its service life. In this case, in all but the warmest climates, 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. For houses with boilers and hot-water heat distribution (radiators, baseboard), the savings from a modern condensing boiler with outdoor reset or equivalent feedback controls can be substantially larger, since the condensing boilers allow reducing the circulating loop temperature almost all the time.
5. Replace hot water heater with efficent model
First, turn down the temperature of your water heater to the warm setting (120°F). 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, not to mention the electricity used for pumping.
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