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How does a Manual Thermostat Work?

B. Turner
B. Turner

A thermostat is a device used for temperature control within a home or commercial building. While newer programmable models offer advanced features and increased levels of efficiency, a standard manual thermostat is operated by hand using a built-in dial or switch. Homeowners can set the thermostat at the desired temperature so the heat or air conditioning switches on and off automatically, or simply turn heating and cooling or or off at the flip of a switch.

Different types of manual thermostat models operate using a variety of different systems. These include mercury indicators, metal contacts or digital systems. While any of these systems can be used to manually control heating and cooling units, each operates slightly differently, and offers its own unique advantages and disadvantages.

Man holding computer
Man holding computer

A mercury-based manual thermostat contains a sealed tube filled with mercury gas. As the temperature in the home changes, the mercury heats up or cools down. After the mercury reaches a specific temperature, the thermostat sends a signal to the heating or cooling unit to switch on or off. Because of the dangers associated with mercury, many of these thermostats are being phased out for newer and safer models.

One of the most operating systems used in the manual thermostat is the bi-metal conductor. These units contain a strip or metal, which can be made from aluminum, tin, steel or some other material depending on the unit. As the room heats up or cools down, the metal reacts to the change in temperature. Once it reaches a specific set point, it sends an electric signal to the furnace or air conditioner to switch on or off. These units tend to be the most affordable, but are also slow to react to temperature changes. While they are effective in the long term, they offer fairly imprecise levels of temperature control.

A manual thermostat may also contain a digital control system, which tends to be the most accurate and reliable of the three systems. With a digital thermostat, an electric temperature gauge senses temperature changes in the room. When the temperature in the room falls above or below the set temperature, the thermostat sends an electric signal to the heating or cooling unit to bring the room's temperature to the desired range. While these units offer the highest level of control for users, they are also the most expensive.

While a manual thermostat is less efficient all around than a programmable unit, there are steps homeowners can take to operate these thermostats more efficiently. By setting the temperature a few degrees less than the desired level in the winter, or a few degrees higher in the summer, homeowners and building managers can significantly improve the efficiency of these thermostats while still maintaining a comfortable temperature range.

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