6. Replace an outdated AC system. With the summer months approaching, now is the perfect time to assess air-conditioning systems. If you are installing or replacing central air, look for an Energy Star label with a seasonal energy-efficiency ratio (SEER) of 13 or greater, which is the new standard, though older models are still being sold. New window air conditioners are nearly twice as efficient as older ones, so springing for a new unit could cut your home cooling bill in half this summer. Look for an energy-efficiency ratio (EFR) of 10 or more for window AC units.