• Schedule an annual tune-up for your central air conditioner, heat pump, or furnace.
• Hire a professional to seal and insulate leaky ducts and to make sure that the airflow distribution system serving your heating equipment is operating efficiently.
• Clean or replace the filters on forced-air furnaces; seal flues in the fireplaces you don’t use; install drapes or other coverings on your windows; and seal holes around your plumbing and heating pipes.
• Check caulking and weatherstripping, and repair if necessary.
• Close any foundation vents in the winter and open them in the summer (if you have a crawl space under your house).
• Install ceiling fans. They’ll cool you off in the summer and promote heating efficiency in the winter.
• Consider a “whole-house” fan. In the summer, it circulates cool air through the house and vents warm air through the attic. It works best at night and when the air outside is cooler than inside.
• Install a computerized thermostat that will automatically lower the indoor temperature at night and when you’re away from home.

Source: Federal Trade Commission