The thermostat is one of most commonly utilized devices today, but often goes unnoticed. Regulating the temperature in homes, offices, and commercial buildings all over the world, this small apparatus has a very big responsibility. Thermostats come in a variety of shapes and sizes with a multitude of functions ranging from basic to “smart.” For now, we will take a look at the basic thermostat and how it works to regulate air temperature.


Definition of basic thermostat

A basic thermostat is a device that functions to establish and regulate a desired temperature. It does this by turning off the air conditioning or heating system when the desired temperature is reached. When the temperature falls below or rises above the desired level, sensors in the thermostat detect this change and will turn the system on until the desired temperature is achieved. The primary function of a thermostat is to maintain the temperature, unlike a thermometer, which measures the temperature.

Your comfort and quality of life often go hand in hand with the ability to heat and cool your home to your desired temperature. But, heating and cooling your home uses a large amount of energy resulting in significant expenses month to month; and it’s the small, unassuming thermostat that regulates and controls one of the most important pieces of equipment in your home. This is why it’s important you not only understand how to properly operate your thermostat, but also how to utilize in a manner that is the most energy efficient.


Brief history of the thermostat

In the 1830s, Andrew Ure invented the bi-metallic thermostat, which employs metal strips that expand when the temperature would increase and cut off the energy supply. In 1885, Albert Butz invented the “damper flapper,” an early prototype of the modern thermostat. His device used a spring motor and crank arm to automatically control the lifting and closing of the damper, which usually needed to numerous times a day by homeowners in an effort to regulate the heat. Butz patented his invention and formed a business which was eventually purchased by, a young engineer named Mark Honeywell. In 1953, the Honeywell company unveiled their iconic, round thermostat, one of the most recognizable thermostat designs in the world and which is still in production today.


Understanding your basic thermostat

A basic thermostat, also known as a “manual” or “non-programmable” thermostat, operates as its name implies: you have to manually turn the dial or move a lever to your desired temperature. There are some basic thermostats that are digitized, where you can just push a button to adjust the temperature to a specific number, but you still have to manually walk up to it to perform this task.

Basic thermostats operate a simple mechanical principle whereby two strips of different metals, usually brass and steel, are welded together and formed into a coil. When exposed to high temperatures, the bimetal strip will expand and uncoil. When the temperature cools down, the bimetallic strip will contract and the coil will tighten. The expansion and contraction of the coil activates contacts on either side of the metal turning the HVAC system on.


How does mercury in a thermostat work?

Mercury is a heavy, silvery-colored liquid metal that moves like water. Within a thermostat, mercury is contained in a vial that tips either to the right or the left based on the expansion or contraction of the bimetallic coil, depending on whether you’ve adjusted the lever on the thermostat to raise or lower the temperature. Wires within the vial allow a current of energy to run through the mercury activating a relay switch that starts your system’s heater or air conditioner. When the temperature or your home starts to heat up (or cool down), a coiled wire gradually unwinds tilting the vial of mercury so that the current is broken and the HVAC system is turned off.

Not sure if your thermostat has mercury or not? Take off the cover of your thermostat and look inside. If you see a glass vial or ampoule containing a silvery-white liquid, then your thermostat has mercury. You can also check the packaging of any new thermostats you buy for “Hg,” which is the symbol for mercury. If you see this, then mercury is in the thermostat.

It is illegal in many cities to dispose of mercury thermostats in the trash. Therefore, it’s important to locate heating and cooling suppliers, or household waste facilities, which will properly dispose of the mercury for you.


Adjusting the basic thermostat

Changing the temperature on a basic thermostat is as easy as pushing a button, moving a lever, or turning a dial. Once you’ve set the thermostat to your desired temperature, your air conditioning system will respond accordingly.


How frequently should my heating and cooling cycle on/off?

A properly working heating and air conditioning system will automatically cycle on and off when the thermostat senses the air is too cold or too warm. Cycling off gives the temperature in your home a chance to regulate as well as saves energy and utility costs. There is no predetermined number of times a system will cycle on and off each hour, nor how long each cycle will run for. Rather, a cooling cycle will last until the air is cooled (or warmed) to the temperature you set on your thermostat. Once the thermostat senses the desired temperature has been reached, it will shut off the system. If the weather is mild outside, your air conditioner will likely run for only a few minutes at a time. During hotter temperatures, it will likely need to run longer to cool the air in your home to your desired setting.

There are other factors which affect how often your system will cycle on and off, such as the size, or tonnage, of your unit, the amount of moisture in the air that needs to be removed, and the temperature outside.


Diagnosing problems – why is the basic thermostat not working? Troubleshooting.

If you suspect your thermostat is not working properly, there are a few things you check before calling a professional for repairs.

  • Remove the thermostat cover and make sure the inside is clean and free of dust, dirt, and residue
  • Check to see if the thermostat box is centered and level, as being askew can affect its internal components.
  • Make sure your thermostat is not exposed to external heat sources or is located in an area that gets direct sunlight.
  • If you have a digital thermostat, check the batteries to see if they need to be replaced.


How do you calibrate a basic thermostat?

If you suspect the setting on your thermostat does not match the temperature of your home, a simple calibration can determine if your thermostat is working properly or not. To calibrate your thermostat, do the following:

  1. Tape a regular glass thermometer to the wall a few inches away from where the thermostat is located. Place some folded paper towels behind it’s not directly touching the wall.
  2. Wait for 15-20 minutes for the mercury to stabilize.
  3. Compare the reading on the thermometer with that on the dial of the thermostat.
  4. If it’s off by more than one degree, remove the thermostat cover and make sure the inside is clean. Gently remove any dust or debris from coils and/or contact points.
  5. If there is a vial of mercury within the thermostat, use a level to make sure it’s not askew. If it is, loosen the screws and adjust the thermostat until it is level.
  6. After cleaning the thermostat and checking that it’s level, repeat steps 1-5. If still not calibrated properly, then the thermostat should be replaced.

It’s important to make sure your thermostat is calibrated properly, otherwise the result could be a utility increase of up to 10%.


What is CPH?

The cycle rate, or “cycle per hour” (CPH) rate, refers to the number of times per hour your HVAC system will turn on and off. Though there are several variables which affect the CPH, it’s typical for a system to cycle on and off 3-6 times an hour. If your system’s CPH is significantly higher or lower, then you should call an HVAC technician right away.


Clear list of steps to operate the basic t-stat

With a basic thermostat, either the ubiquitous round model or the rectangular version, there will be “System” switch with the options setting the system to Heat, Cool, or Off. There may also be a “Fan” switch with the options of Auto or On available. If set to “Auto,” the fan operates when the HVAC system is running. If set to “On,” the fan will run continuously.

To set the thermostat to a desired temperature, just turn the dial or move the lever to a numbered setting listed. For a basic digital thermostat, just punch in a number or hit the up or down arrow buttons to increase or lower the temperature.


Digital and non-digital basic t-stats

Digital thermostats allow for more precise temperature control that moving a lever or dial on a manual thermostat. Just punch in the exact temperature desired, the thermostat will work to maintain it.


The cost of a basic thermostat

Basic, manual thermostats are fairly inexpensive and easy to fix or replace if they stop working. However, if you forget to adjust your thermostat at night or when you’re away from home for long periods of time, then that wasted energy will certainly affect your wallet.


Where a basic thermostat should be located in the home

The thermostat should be located in a place that’s not only convenient for you to easily access it for programming, but also in the part of the home where you and your family spend most of their time. Ideally placed about five feet off the ground, the thermostat should not be located near an outside wall or exposed to any heat sources, such as direct sunlight, heater vents, skylights, windows, or hot-water pipes.

Basic thermostats are inexpensive and easy to use. Many homeowners prefer them to the more complicated programmable or smart thermostats. However, as newer thermostats allow for more precise temperature control and efficiency options saving you money on your utility bill, it may be time to upgrade your basic one.