A typical family spends about a third of its annual heating and cooling budget-roughly $350-on air that leaks into or out of the house through unintended gaps and cracks. With the money you waste in just one year, you can plug many of those leaks yourself. It's among the most cost-effective things you can do to conserve energy and increase comfort, according to Energy Star. Start in the attic, since that's where you'll find some of the biggest energy drains. Then tackle the basement, to prevent cold air that enters there from being sucked into upstairs rooms. Finally, seal leaks in the rest of the house. Here are eight places to start.

1. Insulate around recessed lights

Most recessed lights have vents that open into the attic, a direct route for heated or cooled air to escape. When you consider that many homes have 30 or 40 of these fixtures, it's easy to see why researchers at the Pennsylvania Housing Research/Resource Center pinpointed them as a leading cause of household air leaks. Lights labeled ICAT, for "insulation contact and air tight," are already sealed; look for the label next to the bulb. If you don't see it, assume yours leaks. An airtight baffle ($8-$30 at the home center) is a quick fix. Remove the bulb, push the baffle up into the housing, then replace the bulb.

2. Plug open stud cavities

Most of your house probably has an inner skin of drywall or plaster between living space and unheated areas. But builders in the past often skipped this cover behind knee walls (partial-height walls where the roof angles down into the top floor), above dropped ceilings or soffits, and above angled ceilings over stairs.

Up in the attic, you may need to push insulation away to see if the stud cavities are open. If they are, seal them with unfaced fiberglass insulation ($1.30 a square foot) stuffed into plastic garbage bags; the bag is key to blocking air flow. Close large gaps with scraps of drywall or pieces of reflective foil insulation ($2 a square foot). Once you've covered the openings, smooth the insulation back into place. To see these repairs in action, consult Energy Star's DIY guide to air sealing (http://www.energystar.gov/ia/partners/publications/pubdocs/DIY_Guide_May_2008.pdf).

3. Close gaps around flues and chimneys

Building codes require that wood framing be kept at least one inch from metal flues and two inches from brick chimneys. But that creates gaps where air can flow through. Cover the gaps with aluminum flashing ($12) cut to fit and sealed into place with high-temperature silicone caulk ($20). To keep insulation away from the hot flue pipe, form a barrier by wrapping a cylinder of flashing around the flue, leaving a one-inch space in between. To maintain the spacing, cut and bend a series of inch-deep tabs in the cylinder's top and bottom edges.

4. Weatherstrip the attic access door

A quarter-inch gap around pull-down attic stairs or an attic hatch lets through the same amount of air as a bedroom heating duct. Seal it by caulking between the stair frame and the rough opening, or by installing foam weatherstripping around the perimeter of the hatch opening. Or you can buy a pre-insulated hatch cover kit, such as the Energy Guardian from ESS Energy Products ($150).

5. Squirt foam in the medium-size gaps

Once the biggest attic gaps are plugged, move on to the medium-size ones. Low-expansion polyurethane foam in a can is great for plugging openings 1/4-inch to three inches wide, such as those around plumbing pipes and vents. A standard 12-ounce can ($5) is good for 250 feet of bead about half an inch thick. The plastic straw applicator seals shut within two hours of the first use, so to get the most mileage out of a can, squirt a lubricant such as WD-40 onto a pipe cleaner and stuff that into the applicator tube between uses.

6. Caulk the skinny gaps

Caulk makes the best gap-filler for openings less than 1/4-inch wide, such as those cut around electrical boxes. Silicone costs the most ($8 a tube) but works better next to nonporous materials, such as metal flashing, or where there are temperature extremes, as in attics. Acrylic latex caulk ($2 a tube) is less messy to work with and cleans up with water.

7. Plug gaps in the basement

Gaps low on a foundation wall matter if you're trying to fix a wet basement, but only those above the outside soil level let air in. Seal those with the same materials you'd use in an attic: caulk for gaps up to 1/4-inch wide and spray foam for wider ones. Use high-temperature caulk around vent pipes that get hot, such as those for the furnace or water heater. Shoot foam around wider holes for wires, pipes, and ducts that pass through basement walls to the outside.

In most older houses with basements, air seeps in where the house framing sits on the foundation. Spread a bead of caulk between the foundation and the sill plate (the wood immediately above the foundation), and along the top and bottom edges of the rim joist (the piece that sits atop the sill plate).

8. Tighten up around windows and doors

In the main living areas of your home, the most significant drafts tend to occur around windows and doors. If you have old windows, caulking and adding new weatherstripping goes a long way toward tightening them up. Bronze weatherstripping ($12 for 17 feet) lasts for decades but is time-consuming to install, while some self-stick plastic types are easy to put on but don't last very long. Adhesive-backed EPDM rubber ($8 for 10 feet) is a good compromise, rated to last at least 10 years. Nifty gadgets called pulley seals ($9 a pair) block air from streaming though the holes where cords disappear into the frames.

Weatherstripping also works wonders on doors. If a draft comes in at the bottom, install a new door sweep ($9).

Before working in the attic, take some precautions

Try to do attic work on a cool day. Wear protective gear: disposable clothes, gloves, and a double-elastic mask or half-face respirator. Bring along a droplight with a fluorescent bulb, plus at least two pieces of plywood big enough to span two or three joists to support you as you work. To save trips up and down a ladder, try to move up all of the materials you need before you get started. One warning: If you find vermiculite insulation, hold off until you've had it checked for asbestos; your health department or air-quality agency can recommend a lab.

Jeanne Huber writes a home-repair column for the Washington Post and has commissioned three new roofs on various houses over the years