How Thermostats Work

A thermostat is a temperature sensitive switch that turns the heating and cooling systems on and off when the temperature reaches a set limit. Thermostats can range from a simple manual unit to a sophisticated programmable unit that provides enhanced functionality and energy saving features.

There are four main types of thermostats installed with central air systems. In homes today, it's important that your thermostat is working properly. This will avoid high energy bills from a system over-exerting itself.
  • Mercury Contact (old style; no longer produced)
  • Mechanical Contact
  • Digital
  • Electronic Programmable
The most common type of thermostat sold today is the electronic programmable thermostat. Most programmable thermostats have four settings throughout the day.
  1. Wake Up
  2. Leave
  3. Return
  4. Sleep
Once the thermostat is programmed, if you change the temperature this will cause a temporary override and eventually the temperature will go back to the set temperature. By selecting the hold setting this will maintain the set temperature and will not change.


Set your thermostat conservatively to save energy and if desired only do a temporary override on the temperature.

More Saving Tips

Working Properly

A properly working thermostat will detect and maintain the set temperature. The best location for a thermostat is neat the return air filter where the air mixes and is at an average temperature.

Red Flags

  • HVAC system is un-responsive to temperature adjustments on thermostat
  • Frequent Starts & Stops (short cycling)
  • Corrosion on the battery terminals


To keep your thermostat working, follow these guidelines.

  • Replace thermostat batteries once a year or if thermostat is unresponsive
  • Clean off corroded battery terminals with sand paper or a wire brush
  • If system is short cycling adjust the thermostats heat anticipator settings