Think globally? Act domestically.

Energy-efficient windows can be a good investment, even at a cost of several thousand dollars, but perhaps only if current windows are drafty, Ms. Greenwald says. The federal government's Energy Star website (www.energystar.gov) helps consumers find efficient options among a range of products that meet high- efficiency standards. Example: Superwindows with three panes and low-emissivity.

Once the home is well-sealed, it's time for those in cold climates to look at the furnace. Warm climate dwellers should consider replacing their central air system.

Furnaces manufactured 20 or more years ago are usually only about 50 percent efficient, meaning that only 50 percent of the fuel they consume is converted to heat, Mr. Langholz says. Today's furnaces can be up to 96 percent efficient (96 AFUE rating, for "annualized fuel utilization efficiency"). Replacing a 15-year-old furnace with a high-efficiency model may cut heating fuel usage by 1,000 therms. Last winter in some regions of the US, natural gas rates topped $1 per therm.

Even though natural gas prices can be volatile, homeowners should switch from oil to gas, says Barrien Moore, director of the Institute for the Study of Earth, Oceans and Space at the University of New Hampshire in Durham. He concedes that the switch to cleaner-burning natural gas might be better for the environment than for one's wallet.

"Maybe you never get all of it back. All right, fine," Mr. Moore says. "That is my tax that I'm placing on my personal conduct to try and drive down my carbon emissions." Natural gas burns much more efficiently than oil, he says. It produces less carbon dioxide per Btu produced than does oil.

Other additions can also reduce heating costs.

Rebecca Flora, executive director of the Pittsburgh-based Green Building Alliance, recommends landscaping near the home with deciduous trees to provide cooling shade in summer and warming sunlight in winter. Moore and Ms. Flora both suggest adding a pellet- burning wood stove to a high-traffic area of the home to give the furnace a break. Another tip: Unlike carpet, tile floors retain a wood stove's heat and reduce the need for energy output.

In terms of cooling, a new central air system makes sense, in Langholz's view, if the current one is more than 15 years old, or if the one you have is oversized. Operational savings aren't as dramatic as with heating systems that depend on fossil fuels, since electricity costs haven't spiked in recent years. But because cooling accounts for 11 percent of home energy usage, an Energy Star-rated cooling system can help reduce electric costs by hundreds of dollars per year when combined with strategic appliance upgrades.

If your big-ticket budget isn't exhausted at this point, appliances deserve a good look – especially the older ones.

First stop: the kitchen. The refrigerator alone accounts for 7 percent of an average home's total energy usage, according to the Pew report. What's more, refrigeration efficiencies have come so far in recent years that anyone with a unit more than five years old should consider investing $900 or $1,000 for a unit that's far more efficient, Langholz says.

Just investing in this one appliance "really makes a big difference" for reducing costs and emissions alike, adds Flora.

Other appliances, from dishwashers to clothes dryers, might be worth replacing if they're more than 10 or 20 years old. Rule of thumb: Replace the biggest energy users first, look for Energy Star-rated products, and compare projected operating costs on the Energy Guide label.

Water heaters warrant special consideration, in part for their solar potential. Unlike space heating, water can derive its heat from emission-free solar panels in a way that does not require a supplemental power source. But not all homeowners can afford to wait 10 or even 20 years to recoup the thousands required in an initial capital outlay.

"Solar is definitely coming down [in price], and solar for hot water heating is starting to make sense," especially in San Jose, Calif., and other communities that offer tax credits for solar users, Flora says. But "in a home residential situation, it's still pretty tough to justify economically."

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