Think globally? Act domestically.

Consumers eager to slow global warming increasingly have a financial incentive to think close to home when making choices about where to invest.

Efficiency-enhancing systems, from triple-paned windows to water-saving washers offer more than a boost to a home's long-term value, experts say. They also immediately slash onerous energy bills and shrink a household's "carbon footprint" – the emissions that contribute to global warming.

"The good thing about the recent run-up in energy prices, which is overall tough on a lot of people," says Judi Greenwald, director of innovative solutions at the Pew Center on Global Climate Change in Arlington, Va., "is that it makes the payback for investing in efficiency much quicker,"

Example: Natural gas prices were 50 percent higher this past winter than five years ago. At these new prices, homeowners who pony up an extra $500 to get a high-efficiency feature on a new furnace are likely to see their investment recouped in savings in just two or three years, rather than four or five.

Such demonstrable synergies in the home between what's good both for the planet and the bankbook come at a time when critics are lamenting trade-offs associated with other ethically minded investments. Socially responsible mutual funds, for instance, have in recent years underperformed their unscreened rivals who have invested without hesitation in highly profitable oil companies and weaponsmakers.

What's more, buildings are a major contributor to global warming. According to a June 2005 report from the Pew Center, buildings contribute a larger share of America's carbon dioxide emissions than transportation does. About half of all emissions from buildings, 21 percent of the nation's total output, stem from home-energy consumption. (Think oil-fired furnaces and electrically powered air conditioning.)

But investing profitably in the home isn't as easy as simply buying all the latest technologies. Experts recommend a targeted approach to big-ticket items in order to derive the most bang for the buck. The game plan: Diagnose the biggest inefficiencies, then invest where necessary to collect big rewards. To avoid foolish mistakes, they say, start with an energy audit.

Energy audits pinpoint the physical locations where energy is being wasted. Public utilities routinely offer such services, often through an online analysis of energy bills, free of charge. For a few hundred dollars, a qualified contractor will conduct an on-site analysis and furnish a written report highlighting the opportunity spots.

The greatest potential gains often lurk in the areas of heating and cooling, which together account for 41 percent of energy usage in a typical home. That adds up to more than $600 per year in an average household which, according to the US Department of Energy, spends about $1,500 per year on energy bills.

But before buying new machinery, experts say, invest – if necessary – in making the living environment airtight. Otherwise, the benefits of efficient systems slip through the cracks along with the climate-controlled air.

"If you have any extra bucks, I would say, 'insulate your house,' " says Susanne Moser, a research scientist and public educator at the Institute for the Study of Society and Environment in Boulder, Colo. "We pump so much energy out into the universe by having ... badly insulated homes. That would be a huge difference you could make."

Insulation can cost a few hundred to a few thousand dollars to install, depending on the need. But the return is quick when homeowners spring for high "R" value ratings, says Jeffrey Langholz, an environmental policy expert at the Monterey (Calif.) Institute of International Studies and co-author of "You Can Prevent Global Warming (and Save Money!)." Someone who installs R-38 insulation in a typical 600-square-foot attic, for instance, will save about $225 annually in heating costs. The ecoconscious can use insulation made of recycled denim.

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."