Automatic and Programmable Thermostats
What Is a Thermostat?
It is a temperature-sensitive switch that controls a space conditioning unit or system, such as a furnace, air conditioner, or both. When the indoor temperature drops below or rises above the thermostat setting, the switch moves to the “on” position, and your furnace or air conditioner runs to warm or cool the house air to the setting you selected for your family’s comfort. A thermostat must be manually adjusted to change the indoor air temperature.
General Thermostat Operation Tips
Adjusting for Energy Savings in Winter
You can easily save energy in the winter by setting the thermostat to 68°F (20°C) when you’re at home and awake, and lowering it when you’re asleep or away.
Significant savings can also be obtained by manually or automatically reducing your thermostat’s temperature setting for as little as four hours per day. This is due to a building’s heat loss in the winter, which depends greatly on the difference between the inside and outside temperatures.
For example, if you set the temperature back on your thermostat for an entire night, your energy savings will be substantial. By turning your thermostat back 10° to 15° for 8 hours, you can save about 5% to 15% a year on your heating bill—a savings of as much as 1% for each degree if the setback period is eight hours long, depending on your climate.
Adjusting for Energy Savings in Summer
In the summer, you can save energy on central air conditioning by keeping your house warmer than normal when you are away, and lowering the thermostat setting to 78°F (26°C) only when you are at home and need cooling.
Thermostat Usage – Fact Vs. Fiction
Fiction: The furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings.
Fact: Studies show that fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save.
Fiction: The higher you raise a thermostat, the more heat the furnace will put out, or that the house will warm up faster if the thermostat is raised higher.
Fact: Furnaces put out the same amount of heat no matter how high the thermostat is set—the variable is how long it must stay on to reach the set temperature.
Tips for Thermostats with Automatic Temperature Adjustment
To maximize your energy savings without sacrificing comfort, you can install an automatic setback or programmable thermostat. By maintaining the highest or lowest required temperatures for four or five hours a day instead of 24 hours, a programmable thermostat can pay for itself in energy saved within four years.
Programmable thermostats have features with which you may be unfamiliar. Most of these programmable thermostats perform one or more of the following energy control functions:
- They store and repeat multiple daily settings, which you can manually override without affecting the rest of the daily or weekly program.
- They store six or more temperature settings a day.
- They adjust heating or air conditioning turn-on times as the outside temperature changes.
Types of Automatic and Programmable Thermostats
There are five basic types of automatic and programmable thermostats:
- light sensing
Most range in price from $30 to $250, except for occupancy and light sensing thermostats, which cost around $350.
Electromechanical (EM) thermostats, usually the easiest devices to operate and typically have manual controls. They work with most conventional heating and cooling systems, except heat pumps. EM controls have limited flexibility and store only the same settings for each day. They are best suited for people with regular schedules.
Digital thermostats feature LED or LCD digital readout and data entry pads or buttons. They offer the widest range of features—such as precise temperature control and custom scheduling—and can be used with most heating and cooling systems. Programming some models may be complicated, so make sure you choose one that’s easy for you.
Hybrid systems combine the technology of digital controls with manual slides and knobs to simplify use and maintain flexibility. Hybrid models are available for most systems, including heat pumps.
Occupancy thermostats maintain the setback temperature until someone presses a button to call for heating or cooling. They do not rely on the time of day. The ensuing preset “comfort period” lasts from 30 minutes to 12 hours, depending on how you’ve set the thermostat. These units offer simplicity, but lack flexibility. They are ideal for spaces that are unoccupied for long periods of time.
Light sensing heat thermostats rely on the lighting level preset by the owner to activate heating systems. When lighting is reduced, the thermostat senses unoccupied conditions and allows space temperatures to fall 10° below the occupied temperature setting. When lighting levels increase to normal, temperatures automatically adjust to comfort conditions. These thermostats are designed for stores and offices.
Choosing a Programmable Thermostat
It’s wise to learn as much as you can before selecting a programmable thermostat. When shopping, bring information with you about your current unit, including the brand and model number. Also, ask these questions:
- Does the unit’s clock draw its power from the heating systems’ low-voltage electrical control circuit instead of a battery? If so, is the clock disrupted when the furnace cycles on and off? Battery-operated, back-up thermostats are preferred by many homeowners.
- Is the thermostat compatible with the electrical wiring found in your current unit?
- Are you able to install it yourself, or should you hire an electrician or a heating, ventilation, and air conditioning (HVAC) contractor?
- How precise is the thermostat?
- Are the programming instructions easy to understand and remember? Some thermostats have the instructions printed on the cover or inside the housing box. Otherwise, will you have to consult the instruction booklet every time you want to change the setback times?
Most automatic and programmable thermostats completely replace existing units. These are preferred by many homeowners. However, some devices can be placed over existing thermostats and are mechanically controlled to permit automatic setbacks. These units are usually powered by batteries, which eliminates the need for electrical wiring. They tend to be easy to program, and because they run on batteries, the clocks do not lose time during power outages.
Chart Your Thermostat Usage Before You Buy
Before you buy a programmable thermostat, chart your weekly habits including wake up and departure times, return home times, and bedtimes, and the temperatures that are comfortable during those times. This will help you decide what type of thermostat will best serve your needs.
Where to Place Your Thermostat
The location of your thermostat can affect its performance and efficiency. Read the manufacturer’s installation instructions to prevent “ghost readings” or unnecessary furnace or air conditioner cycling. Place thermostats away from direct sunlight, drafts, doorways, skylights, and windows. Also make sure your thermostat is conveniently located for programming.
A Note for Heat Pump Owners: When a heat pump is in its heating mode, setting back a conventional heat pump thermostat can cause the unit to operate inefficiently, thereby canceling out any savings achieved by lowering the temperature setting. Maintaining a moderate setting is the most cost-effective practice. Recently, however, some companies have begun selling specially designed setback thermostats for heat pumps, which make setting back the thermostat cost effective. In its cooling mode, the heat pump operates like an air conditioner; therefore, manually turning up the thermostat will save you money.
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