A thermostat is a device that is used to control a heating or cooling system so that it maintains a certain temperature or keeps the temperature within a certain range. In a home, for example, this device can automatically turn on the heating system when the temperature in the home drops or turn on the air conditioning when it gets too hot. As the warm or cool air fills the room and the desired temperature is achieved, the device then turns off the system. There are two main types of thermostats: mechanical and digital. Many digital thermostats also are programmable, which allows a user to set different preferred temperatures for different times of the day or days of the week.
Mechanical Thermostats
A mechanical thermostat uses physical means to gauge the air temperature and activate a switch that turns on a heating or cooling system on turns it off. There are several types of sensor technology that can be used in mechanical thermostats, such as bimetallic strips, wax pellets, bulbs filled with gas or tubes filled with air. Each of these types of sensors will react to changes in temperature, such as by expanding or contracting, and will trigger the proper switch to raise or lower the temperature. Bulbs filled with mercury were once commonly used in thermostats, but its use has been discontinued or outlawed in many places because of the dangers of mercury.
The most common of these technologies in home thermostats is the bimetallic strip. This technology uses two thin strips of different metals — such as copper and iron, copper and steel and brass and steel — bonded together and rolled into a coil. As the temperature changes, the different metals expand or contract at different rates, causing the strip to bend. When the strip bends enough to touch an electrical contact and complete an electrical circuit, it turns on the heating or cooling system. If the temperature changes enough to unbend the strip, contact is lost, and the system turns off.
Digital Thermostats
Many homes now have digital thermostats, which use electronic sensors instead of physical means to monitor changes in temperature. Based on the temperatures read by the electronic sensors, these devices turn on or off the cooling or heating systems as needed. A digital thermostat usually requires one or more batteries for power. Buttons and switches allow the user to control the settings, and a display screen shows the settings as well as the current temperature.
Setting a Thermostat
To set a mechanical thermostat, the user typically must turn a dial or move a lever. One common type of mechanical thermostat has a dial that has a range of temperatures printed on it, and the user simply turns the dial until a small arrow or line is on the preferred temperature. Another type is rectangular and has two levers that allow the user to set a minimum temperature and a maximum temperature. These thermostats often also have switches that allow the user to turn on or off the heating or cooling system as well as any ventilation fans that might be part of the system.
When setting digital thermostats, in most cases, the users simply look at the display screens and push buttons to input the desired settings. Some newer models feature touch screens instead of separate buttons and display screens. For a programmable model, the user could choose to have different setting for certain times, such as when the home's residents are sleeping, when they are first waking up or when they are away at work or school. Programmable settings not only can make a home more comfortable, they also can conserve energy by keeping the heating or cooling system from turning on or off unnecessarily, such as when nobody is home. Depending on the model, these programmed times might be when the device begins adjusting the temperature, or the device might begin working earlier so that the desired temperature is achieved at the programmed time.
Ideal Home Settings
Most people set their thermostats to the temperatures or ranges at which they are the most comfortable. Some people, however, prefer to conserve energy and save money by adjusting their settings by a few degrees. Many people consider the most comfortable room temperatures to be about 70° Fahrenheit (21.1° Celsius) to 72° Fahrenheit (22.2° Celsius). Most people don't notice the difference between 72° Fahrenheit (22.2° Celsius) and 74° Fahrenheit (23.3° Celsius), for example, so setting a thermostat to turn on the air conditioning at the slightly higher temperature can save energy and money without significantly affecting the comfort level in the home.
Some experts recommend setting a home's thermostat so that the heat turns on at 67° Fahrenheit (19.4° Celsius) and the cooling system turns on at 77° Fahrenheit (25.6° Celsius). These settings can be adjusted for different seasons of the year, partly because people generally wear more clothes during colder months and less clothes during warmer months, no matter whether they are inside or outside. People often are more comfortable sleeping at lower temperatures, so programmable thermostats could be set to allow the temperature to drop to about 62° Fahrenheit (16.7° Celsius) during normal sleeping hours.