Energy efficiency "may be the farthest-reaching, least-polluting and fastest-growing U.S. energy success story of the last 50 years," says the American Council for an Energy-Efficient Economy.

They've been promoting it, of course, but they keep running up against common myths that confuse people. Is it possible to change the thermostat too much? Should you warm up your car or not?

Today, they've released a list of 10 mythbusters, and here they are:

MYTHBUSTING FACT #1: Turning off lights, even for short periods of time, really saves energy, with little impact on the lifespan of the bulb.  Turn off the lights even when you’re leaving a room for just a few minutes.

MYTHBUSTING FACT #2: Today's compact fluorescent lightbulbs work just as well as incandescents, and are just as safe. CFLs have come a long way in terms of quality and variety, and use a fraction of the energy of incandescent bulbs. Look for the ENERGY STAR label to ensure high quality bulbs, and try out different color varieties to find the one you like best (“soft white” most closely mimics the color of an incandescent). As for safety, even if a bulb breaks in your house authorities suggest that there is not enough mercury in the bulb to present a substantial health hazard. That being said, efforts should be taken to dispose of CFLs properly.

MYTHBUSTING FACT #3: Don't spend time warming up the car when it’s cold outside. While it is best to avoid stressing the car while the engine is cold, simply drive a bit more “gently” for the first few minutes. Also, idling a modern car always wastes more energy than turning it off (even for short periods of time).

MYTHBUSTING FACT #4: Turn down the thermostat while you’re away from the house for the day. If you are out for a good stretch of time (say 8 hours or so), this temperature "set-back" will save more energy than it will take to bring your home back to the desired temperature. (Note: If you have a heat pump, make sure you have a heat pump thermostat that has been properly programmed.)

MYTHBUSTING FACT #5: Don’t forget the simple maintenance needed to keep your heating and air-conditioning systems running efficiently. Change the air filter regularly (once a month during heating and cooling season) and get a “tune-up” by a contractor every 2 to 3 years.

MYTHBUSTING FACT #6: While heating and air-conditioning equipment is much more efficient than it used to be, there are still significant variations in energy use. The most important decision is which contractor to choose, so the equipment will be the right size and installed properly, and the ductwork will be fixed so that it doesn’t leak a quarter of the energy you buy (the US average)!  Qualified contractors will ask about comfort issues, run a real load calculation program so they won't need to sell oversized equipment, and discuss options with you. Premium equipment offers even better efficiency, and features such as quieter operation and better humidity control.

MYTHBUSTING FACT #7: Refrigerators, clothes washers, and dishwashers on the market today are much more efficient than those available ten or twenty years ago, but there are still significant differences in energy use among models.  For example, side-by-side refrigerator/freezers generally use more energy than freezer-on-top models. Features such as icemakers also use extra energy. Most front-loading clothes washers save significant amounts of energy and water compared to conventional top-loading designs. On the other hand, products like stoves vary relatively little in their inherent efficiency.

MYTHBUSTING FACT #8: The best way to save energy for your computer is to turn it off when you’re not using it. The second best way is to set it to automatically go into “sleep” or “hibernate” mode to save energy. Also, make sure the next computer you purchase has an ENERGY STAR label. Contrary to popular belief, using a screensaver saves no energy.

MYTHBUSTING FACT #9: Energy-efficient windows save energy, but a window replacement is unlikely to pay for itself in energy savings alone.  If you need to replace your windows for other reasons, the premium you’ll pay for high performance windows (ENERGY STAR or better) is generally worth the investment. And like so many other major energy efficiency projects, much of the energy savings depends on the quality of the contractor you hire to do the work. Bad installations can not only leak and cause drafts, but can also lead to major moisture damage.

MYTHBUSTING FACT #10: While energy-efficient windows are a step in the right direction, walls always outperform windows. Be careful not to choose oversized windows, and take extra steps to increase the performance of windows, such as shading for western- and southern-facing windows.