To calculate energy savings with increased insulation Fuel Comparison To compare heating costs using various fuels. To size a room air conditioner. Thermostats, aquastats, relays, timers or sequencers, are basically on and off switches.
Thermostats can be mechanical or electronic.
Mechanical thermostats make use of the expansion rate of different metals. By welding two flat pieces of dissimilar metals together to make a bar, movement will occur favoring one side or the other as the bar is heated or cooled. Using the bar as a lever, with one end fixed in place, movement of the other end from temperature changes can be used to switch the heating or cooling on. Some manufactures attach glass bulbs with a bead of liquid mercury and electrical contacts inside to the lever for more accurate temperature sensing and switching. Correct mounting of a mercury bulb thermostat is critical to it's accuracy.