page_title: Programmable thermostat
section_title: Clock thermostats
hierarchical_section_title: Programmable thermostat / Construction and features / Clock thermostats
caption_attribution_description: English: Thermostat for controlling the temperature in an office building. It is made by en:Honeywell and uses a en:bimetallic strip. Photo by Dante Alighieri
context_page_description: A programmable thermostat is a thermostat which is designed to adjust the temperature according to a series of programmed settings that take effect at different times of the day. Programmable thermostats are also known as setback thermostats or clock thermostats.
context_section_description: The most basic clock thermostats may only implement one program with two periods (a hotter period and a colder period), and the same program is run day after day. More sophisticated clock thermostats may allow four or more hot and cold periods to be set per day. Usually, only two distinct temperatures (a hotter temperature and a colder temperature) can be set, even if multiple periods are permitted. The hotter and colder temperatures are usually established simply by sliding two levers along an analogue temperature scale, much the same as in a conventional (non-clock) thermostat.
  This design, while simple to manufacture and relatively easy to program, sacrifices comfort on weekends since the program is repeated each of the seven days of the week with no variation. To overcome this deficit, a push-button is sometimes provided to allow the user to explicitly switch (once) the current period from  hot period to a cold period or vice versa; the usual use of this button is to over-ride a "set back" that takes place during the workday when the home is normally unoccupied.
  The clock mechanism is electrical. Two methods have commonly been used to operate it:
  [1] A separate, continuous source of 24 volts alternating current (24 VAC) is provided to the thermostat.
  [2] A rechargeable battery in the thermostat operates the clock. This battery charges when the thermostat is not calling for heat and 24 VAC is available to it. It discharges to operate the clock when the thermostat is set for heating or cooling.
caption: Honeywell office thermostat
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