Program your thermostat to turn heat down or air-conditioning up when you’re out. If your furnace is more than 10 to 15 years old, or your boiler is more than 20 years old, replace it with a model approved by the federal government’s Energy Star program (marked by rating stickers in stores). It will pay for itself in energy savings in 5 to 10 years.

Seal your house: Close the fireplace damper; install a timer (available at hardware stores) on the bathroom exhaust fan; seal ductwork.

Cool your home naturally: Open windows on cool summer nights. Use energy-saving compact fluorescent bulbs (they emit less heat). Hang washing out to dry, and grill food outside. Install window awnings. Plant deciduous trees on the east and west to shade your house and cool it by as much as 20 degrees.

Install an Energy Star–certified ceiling fan (50 percent more efficient than others) and comfortably keep your home four degrees warmer in the summer.

Consider switching to a natural-gas water heater (which uses less than half the energy of an electric one), and turn the setting down to 120 degrees.

Potential Savings: About $500 a year.

Green Point: If one household in 10 bought Energy Star–rated heating and cooling equipment, the change in greenhouse-gas emissions would be equivalent to taking 1.5 million cars off the road.