Cost: $200 to $750
Sachs recommends getting a "Home Energy Rating System" review or other comprehensive audit of your property's fuel efficiency before even thinking about installing a solar panel or new air conditioner. "Instead of just blindly throwing money at energy efficiency, you want to invest in a consultant with the right tools and get the right 'road map' of what to do," he says. Home-energy audits typically take around a half-day and involve checking your home's heating and cooling systems, as well as using high-tech infrared heat detectors and negative-air-pressure machines to find gaps in your property's insulation. Audits typically cost a few hundred dollars, but your local utility or state energy commission will sometimes offer them for free or at a reduced cost. Fix your home's "envelope"
Cost: $4,000 to $5,500
Once you've done an energy audit, you should fix any gaps the review has uncovered in your home's "envelope" -- the insulation that separates heated or cooled living spaces from unheated attics or the outdoors.