Knock $4,000 Off Your Utility Bill

Invest $1,500 in insulation and maintenance and get over twice that in energy savings the first year.

Insulate Your Attic

Cost: $500 to $1,000

Payback: $500 to $1,000 a year

"The attic floor is the house's most important barrier to heat loss because heat rises," says Charley Cormany, project manager at Renu, a home energy performance contractor in San Anselmo, Calif.

The thickness of the insulation between joists in the unfinished floor should be at least 10 to 12 inches. If it isn't, lay on additional rolls, or "batts."

You should also insulate a pull-down door or hatch with an attic tent. Made of fabric-covered insulating material, it keeps out drafts but allows you access through a zippered flap ($200 from attictent.com).

Cover the Ducts

Cost: $50 to $250

Payback: $500 to $1,500 a year

Inspect heating and cooling ducts in the attic, basement and closets. If you find exposed metal ducts, cover the seams with foil tape (such as Scotch Duct Sealing Foil Tape, $6 at acehardwaresuperstore.com) to plug any leaks.

Then cover the entire duct with insulation (such as Thermwell Self- Adhesive Foil/Foam Duct Insulation, $18 for 15 feet at homedepot.com) and you can save as much as 50% on heating and cooling costs.

Use Time Settings for Heat

Cost: $40

Payback: $500 a year

Install a programmable thermostat (such as Honeywell's 5-2 Programmable Thermostat, $40; available at lowes.com).

You can set it to lower the heat automatically just after you've gone to bed and to warm up the house before the alarm clock rings so that you won't have to put on an overcoat when you wake up.

If you lower the thermostat by 7° from the normal daytime temperature, you'll knock 10% off your heating costs. Connecting the unit is a (warm) breeze; you merely unscrew the low-voltage wires and attach them to the new thermostat.

Seal Those Cracks

Cost: $15

Payback: $500 a year

If your attic or basement is unfinished, use a can of expanding foam insulation (such as Great Stuff Insulating Foam, $5 at deerso.com) to seal holes in the attic floorboards and basement ceilings.

That could reduce heating and cooling costs by about 10%. "Electricians and plumbers turn ceilings and floors into Swiss cheese when they run their pipes and wires," says Cormany.

You may also see gaps around the chimney or around recessed lighting. Ask at the home center for heat-resistant insulation for those spots.

Wrap Your Water Heater

Cost: $40

Payback: $100 a year

Drape a water-heater blanket - really nothing more than an overcoat - around your tank to keep heat from leaking away.

Also, wrap pipe insulation around the first five feet of both the hot-water outlet pipe and the cold-water pipe leading into the tank. You can find the stuff at any hardware or plumbing-supply store.

Taking these measures will knock as much as 15% off the unit's operating costs.

Call for Service

Cost: $100 to $200 per unit a year

Payback: $300 to $500 a year

Cleaning your furnace's oil burners or removing scale from gas units, changing filters and checking refrigerant levels in the air-conditioning system are not exactly do-it-yourself jobs. You'll need some help from the professionals.

For every year that you fail to schedule service for your furnace (gas or oil), you'll wind up using 5% more heating fuel because of all the gunky buildup, and you'll pay 10% to 30% extra for neglecting your central air conditioning.