DOE/GO-10097-375 FS 215 ENERGY March 1997 EFFICIENCY Automatic and AND

RCLEARINGHOUSEENEWABLE Programmable ENERGY In our modern, high-tech society, we don’t no savings. This misconception has been think much about some of the electronic dispelled by years of research and numer- gadgets in our homes. Take, for example, ous studies. The fuel required to reheat a the ever-present —a staple of building to a comfortable temperature is American households for decades. It usu- roughly equal to the fuel saved as the ally takes the shape of an unassuming box building drops to the lower temperature. on the wall, but that modest device controls You save fuel between the time that the the comfort of your family on the coldest temperature stabilizes at the lower level day in January and the hottest day in July. and the next time heat is needed. So, the longer your house remains at the lower What Is a Thermostat? temperature, the more energy you save. It is a temperature-sensitive switch that Another misconception is that the higher controls a space conditioning unit or sys- you raise a thermostat, the more heat the tem, such as a , air conditioner, or furnace will put out, or that the house will both. When the indoor temperature drops warm up faster if the thermostat is raised below or rises above the thermostat set- higher. put out the same amount ting, the switch moves to the “on” posi- of heat no matter how high the thermostat tion, and your furnace or air conditioner is set—the variable is how long it must runs to warm or cool the house air to the stay on to reach the set temperature. setting you selected for your family’s com- fort. A thermostat, in its simplest form, In the winter, significant savings can be must be manually adjusted to change the obtained by manually or automatically indoor air temperature. reducing your thermostat’s temperature General Thermostat Operation setting for as little as four hours per day. These savings can be attributed to a build- You can easily save energy in the winter ing’s heat loss in the winter, which by setting the thermostat to 68°F (20°C) depends greatly on the difference between when you’re at home and awake, and low- the inside and outside temperatures. For ering it when you’re asleep or away. This example, if you set the temperature back strategy is effective and inexpensive if you on your thermostat for an entire night, are willing to adjust the thermostat by your energy savings will be substantial. hand and wake up in a chilly house. In the By turning your thermostat back 10° to 15° summer, you can follow the same strategy for 8 hours, you can save about 5% to 15% with central , too, by keep- a year on your heating bill—a savings of ing your house warmer than normal when as much as 1% for each degree if the set- you are away, and lowering the thermo- back period is eight hours long. The per- stat setting to 78°F (26°C) only when you centage of savings from setback is greater are at home and need cooling. for buildings in milder climates than for those in more severe climates. In the sum- A common misconception associated with mer, you can achieve similar savings by thermostats is that a furnace works harder keeping the indoor temperature a bit than normal to warm the space back to a higher when you’re away than you do comfortable temperature after the thermo- when you’re at home. stat has been set back, resulting in little or

NT O ME F E T N R E A R This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. P G

E Y D The document was produced by the Information Services Program, under the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiency

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A N and Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based on C I I T R E information known to EREC and NREL at the time of printing. No recommendation or endorsement of any product or service is implied if mentioned by EREC. D E M S A TAT ES OF Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste

But there is a certain amount of inconve- without affecting the rest of the daily or A Note for Heat nience that results from manually control- weekly program. Pump Owners ling the temperature on your thermostat. • They store six or more temperature set- When a is in its This includes waking up in a cooler than tings a day. heating mode, setting back normal house in the winter and possibly • They adjust heating or air conditioning a conventional heat pump forgetting to adjust the thermostat (during turn-on times as the outside tempera- thermostat can cause the any season) when you leave the house or ture changes. unit to operate ineffi- go to bed. ciently, thereby canceling out any savings achieved Most programmable thermostats have liq- by lowering the tempera- Thermostats with Automatic uid crystal temperature displays. Some ture setting. Maintaining a Temperature Adjustment have back-up battery packs that eliminate moderate setting is the the need to reprogram the time or clock in most cost-effective prac- To maximize your energy savings without case of a power failure. New programma- tice. Recently, however, sacrificing comfort, you can install an auto- ble thermostats can be programmed to some companies have matic setback or programmable thermo- begun selling specially accommodate life style and control heat- designed setback ther- stat. They adjust the temperature setting ing and cooling systems as needed. mostats for heat pumps, for you. While you might forget to turn which make setting back down the heat before you leave for work the thermostat cost effec- Types of Automatic and in the morning, a programmable thermo- Programmable Thermostats tive. In its cooling mode, stat won’t! By maintaining the highest or the heat pump operates like an air conditioner; lowest required temperatures for four or There are five basic types of automatic and therefore, manually turn- five hours a day instead of 24 hours, a pro- programmable thermostats: ing up the thermostat will grammable thermostat can pay for itself in save you money. energy saved within four years. • electromechanical, • digital, Programmable thermostats have features • hybrid, with which you may be unfamiliar. The • occupancy, and newest generation of residential thermo- • light sensing. stat technologies is based on microproces- sors and thermistor sensors. Most of these Most range in price from $30 to $100, programmable thermostats perform one except for occupancy and light sensing or more of the following energy control thermostats, which cost around $200. functions: Electromechanical (EM) thermostats, usu- • They store and repeat multiple daily set- ally the easiest devices to operate, typi- tings, which you can manually override cally have manual controls such as movable tabs to set a rotary timer and sliding levers for night and day tempera- Electromechanical Thermostat ture settings. These thermostats work with most conventional heating and cooling 50 60 70 80 systems, except heat pumps. EM controls have limited flexibility and can store only

the same settings for each day, although at

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4 least one manufacturer has a model with

12 50 60 70 80 M

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G EM thermostats are best suited for people 7

12 with regular schedules. 8 12 9 Digital thermostats are identified by their 12 10

12 LED or LCD digital readout and data 11 12 entry pads or buttons. They offer the N 12 O O 1 12 N 12 12 widest range of features and flexibility, and digital thermostats can be used with most heating and cooling systems. They provide precise temperature control, and Electromechanical thermostats have internal programming wheels that track the they permit custom scheduling. Program- time of day and night. Pins or tabs in the wheel trigger the heating or cooling ming some models can be fairly compli- system to start or shut off.

2 selves after power failures. Light sensing Digital Thermostat thermostats are designed primarily for stores and offices where occupancy deter- mines lighting requirements, and there- fore heating requirements.

Choosing a Programmable Thermostat Set Current Day/Time Day Setting Because programmable thermostats are a relatively new technology, you should Hold Temp Morning Daytime Temp learn as much as you can before selecting a unit. When shopping for a thermostat, Run Program Night Evening Time bring information with you about your

ON AUTO HEATOFF COOL current unit, including the brand and model number. Also, ask these questions before buying a thermostat:

Digital thermostats are programmed with electronic keys or buttons, and many • Does the unit’s clock draw its power can be programmed with different schedules for weekdays and weekends. from the heating systems’s low-voltage electrical control circuit instead of a bat- cated; make sure you are comfortable with tery? If so, is the clock disrupted when the functions and operation of the thermo- the furnace cycles on and off? Battery- stat you choose. Remember— you won’t operated back-up thermostats are pre- save energy if you don’t set the controls or ferred by many homeowners. you set them incorrectly. • Is the thermostat compatible with the By turning your electrical wiring found in your current Hybrid systems combine the technology unit? thermostat back 10° to of digital controls with manual slides and • Are you able to install it yourself, or knobs to simplify use and maintain flexi- should you hire an electrician or a heat- 15° for 8 hours, you bility. Hybrid models are available for ing, ventilation, and air conditioning most systems, including heat pumps. (HVAC) contractor? can save about 5% to • How precise is the thermostat? Occupancy thermostats maintain the set- • Are the programming instructions easy 15% a year on your back temperature until someone presses a to understand and remember? Some button to call for heating or cooling. They thermostats have the instructions printed heating bill—a do not rely on the time of day. The ensu- on the cover or inside the housing box. ing preset “comfort period” lasts from 30 Otherwise, will you have to consult the savings of as much as minutes to 12 hours, depending on how instruction booklet every time you want you’ve set the thermostat. Then, the tem- to change the setback times? 1% for each degree if perature returns to the setback level. These units offer the ultimate in simplicity, Most automatic and programmable ther- the setback period is but lack flexibility. Occupancy thermostats mostats completely replace existing units. are best suited for spaces that remain These are preferred by many homeown- eight hours long. unoccupied for long periods of time. ers. However, some devices can be placed over existing thermostats and are mechan- Light sensing heat thermostats rely on the ically controlled to permit automatic set- lighting level preset by the owner to acti- backs. These units are usually powered by vate heating systems. When lighting is batteries, which eliminates the need for reduced, a photocell inside the thermostat electrical wiring. They tend to be easy to senses unoccupied conditions and allows program, and because they run on batter- space temperatures to fall 10° below the ies, the clocks do not lose time during occupied temperature setting. When light- power outages. ing levels increase to normal, tempera- tures automatically adjust to comfort conditions. These units do not require bat- teries or programming and reset them-

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minimize the use of backup electric resis- Mon. Tue. Wed. Thu. Fri. Sat. Sun. tance heat systems. Electric resistance sys- 6:00am 6:00am 6:00am 6:00am 6:00am 8:00am 8:00am tems, such as electric baseboard heating, 68°F 68°F 68°F 68°F 68°F 68°F 68°F also require thermostats capable of directly controlling 120 volt or 240 volt line-voltage 7:30am 7:30am 7:30am 7:30am 7:30am —— circuits. Only a few companies manufac- 60°F 60°F 60°F 60°F 60°F —— ture line-voltage setback thermostats. 5:00pm 5:00pm 5:00pm 5:00pm 5:00pm —— A Simpler Way to Control 68°F 68°F 68°F 68°F 68°F — — Your Environment 10:00pm 10:00pm 10:00pm 10:00pm 10:00pm 10:30pm 10:30pm The best thermostat for you will depend 62°F 62°F 62°F 62°F 62°F 62°F 62°F on your life style and comfort level in varying house temperatures. While auto- Before you buy a programmable thermostat, chart your weekly habits including matic and programmable thermostats save wake up and departure times, return home times, and bedtimes, and the temperatures that are comfortable during those times. This will help you decide energy, a manual unit can be equally effec- what type of thermostat will best serve your needs. tive if you diligently regulate its setting— and if you don’t mind a chilly house on winter mornings. If you decide to choose Other Considerations an automatic thermostat, you can set it to The location of your thermostat can affect raise the temperature before you wake up A programmable its performance and efficiency. Read the and spare you some discomfort. It will manufacturer’s installation instructions to also perform consistently and dependably thermostat can prevent “ghost readings” or unnecessary to keep your house at comfortable temper- furnace or air conditioner cycling. Place atures during the summer heat, as well. pay for itself in thermostats away from direct sunlight, drafts, doorways, skylights, and windows. energy saved within Also make sure your thermostat is conve- niently located for programming. four years. Some modern heating and cooling sys- tems require special controls. Heat pumps are the most common and usually require special setback thermostats. These ther- mostats typically use special algorithms to

Source List The Energy Efficiency and Renewable Energy “Good News on the ‘Setback’ Front,” T. Wilson, Home Clearinghouse (EREC) Energy, Jan-Feb 1991. 2124 Kittredge Street, No. 95, P.O. Box 3048 Berkeley, CA 94704, (510) 524-5405. Merrifield, VA 22116 (800) 363-3732 “Home Environment,” Home Mechanix, February 1992. Fax: (703) 893-0400 “Home Q&A,” Home Mechanix, November 1995. E-mail: [email protected] EREC provides free general and technical information to the “The Latest in Home Thermostats,” Consumers’ Research public on the many topics and technologies pretaining to Magazine, February 1990. energy efficiency and renewable energy. “New Electronic Thermostats Save Money,” Consumers Digest, January 1989. Reading List “Programmable Thermostats: How to Buy and Install “Electronic Thermostats,” Radio-Electronics, June 1992. One in Your Home,” Family Handyman, January 1989. “Energy Saving Thermostats,” Consumer Reports, “Smart Thermostats for Comfort and Conservation,” October 1993. March 1994, EPRI Journal.

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