High-Tech Thermostats

Programmable thermostats make it easy to preset a week's worth of temperatures -- and give you much greater control over energy bills. For instance, you could program the gadget to lower the temperature when everyone's asleep, something you might forget to do on a nightly basis.

COST: $50 to $150.

PAYBACK: About a year, assuming the thermostat controls both heating and cooling.

How'd we arrive at that figure? We turned to a calculator on the Web site for the Department of Energy's EnergyStar program. The tool shows you how much these advanced thermostats will save you. (One caveat: The estimates assume you have natural-gas heat and electric central cooling.)

Let's use the calculator to look at two cities -- Fargo, N.D., where electricity rates are low but where lots of heat is needed in the winter, and Las Vegas, which has higher rates and needs lots of cooling in the summer. And let's say you use the thermostat to make modest temperature changes at night, lowering it to 62 from 70 in cold months, and raising it to 82 from 78 when the weather's warm.

In Fargo, the thermostat would save you about $115 on heating and cooling annually -- so you'd make back the cost within a year if you spent $100. In Las Vegas, you'd save about $75 and make your money back in a little over a year.

What's more, some utilities will install the thermostats free in exchange for letting them scale back your central air-conditioning use remotely on hot summer days. Many utilities also offer rebates on these devices.

Smarter Water Heating

Drain-water heat-recovery systems warm up water for your shower by capturing the heat from waste wate going through, at a cost of abo the panels aren't generating an