Seal the envelope

Small cracks and gaps in your house's shell can allow about a third of the heat and air conditioning in a 10-year-old house to escape, says Peter Scheckel, an analyst at the Vermont Energy Investment Corporation, a nonprofit energy-efficiency services company.

In the attic, look for gaps around anything that comes through the floor, such as pipes, fan ducts and electrical lines. Use an expanding-foam spray or paint-able caulk to seal cracks.

Annual savings: Up to 10% on your fuel bills

Up-front cost: About $100 if you do it yourself; $500 or more if you hire out the job.

Tax credit: 10% of the cost of storm windows (credit cannot exceed $200).