Most thermostats have three layers.See more pictures of thermostats.

You've probably seen or used a thermostat a thousand times. This device controls the heating and air-conditioning systems in your house -- the two pieces of equipment that use the most energy. In these days of rising energy prices, you might be interested to see how your thermostat works. It is surprisingly simple and contains some pretty neat technology.

In this article, we'll take apart a household thermostat and learn how it works. We'll also learn a little about digital thermostats, talking thermostats, telephone thermostats and system zoning. Let's start by taking a look at the parts of a basic thermostat.

The top layer houses the mercury switch and the thermometer coil. The bottom layer houses the circuit card, the mode switch and the fan switch.

The mercury switch is a glass vial with a small amount of mercury in it. Mercury is a liquid metal -- it conducts electricity and flows like water. Inside the glass vial are three wires. One wire goes all the way across the bottom of the vial, so the mercury is always in contact with it. One wire ends on the left side of the vial, so when the vial tilts to the left, the mercury contacts it -- making contact between this wire and the one on the bottom of the vial. The third wire ends on the right side of the vial, so when the vial tilts to the right, the mercury makes contact between this wire and the bottom wire.

­The mercury switch

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­ ­There are two thermometers in this thermostat. The one in the cover displays the temperature. The other, in the top layer of the thermostat, controls the heating and cooling systems. These thermometers are nothing more than coiled bimetallic strips. We'll look at them in more detail next.

Going Green Adjusting your thermostat and shortening your showers aren't the only easy ways to go green. Learn lots more about how you can make a difference at Discovery Planet Green.

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