Programmable thermostats are a type of heating and cooling control that allows different temperature settings during different times of the day or week. They save energy because they call for heating or cooling according to a personalized schedule, turning systems on when people are likely to be home in the morning and evening, and automatically setting back the temperature at night.
The primary environmental benefit of using or switching to programmable thermostats is energy savings. This reduction in energy use saves the user money and reduces the negative environmental impacts of energy production.
Notes on Use
For new construction, a programmable thermostat is installed in the same manner as any other thermostat. For replacing older thermostats with a newer model, it is important to ensure the compatibility of the system. Most new thermostats are designed to be compatible with existing wiring and can be easily installed. In homes with multiple furnaces and zones (separately controlled areas of the home) one thermostat is necessary for each heating and cooling zone, with separate programs for each, corresponding to the use of that zone. Thermostats should be placed in an easily accessible central location away from sunlight, heating and cooling vents, and doorways and windows.
Heat Pump Systems
Special care should be taken in pairing a thermostat with a heat pump system.1 Heat pumps used in their heating mode operate less efficiently when they do not run continually, as they rely on electric coil resistance heat for quick response time. There are some thermostats available that are designed specifically for heat pumps. These can save energy during the heating mode. When using a programmable thermostat with a heat pump, it is advisable to purchase a programmable thermostat designed specifically for a heat pump or operate a standard programmable thermostat only for cooling (when the heat pump works like an air conditioner).
Electric Resistance Heating Systems
Programmable thermostats specifically designed for high-voltage switching are necessary for electric resistance heating systems like electric baseboard heating.2
Steam and Radiant Floor Systems
Because of the slow response time of steam and radiant floor heating3 systems, steam and radiant floor heating require more advanced thermostats with adaptive or smart recovery features that track the performance and the temperatures of the home and continually adjust schedules to maximize efficiency and comfort.
Options and Analysis
Programmable Thermostat Types
7-day: These thermostats have programmable settings for each day of the week and are best for those whose schedules change during the week. These are the most flexible, but may require the most effort to set.
5+2 day: These thermostats have one setting for the days of the week and another setting for the weekend.
5-1-1 day: These thermostats have one setting for weekdays and a setting for each of the weekend days. This allows for different schedules between weekend days.
Some programmable thermostats have only a one day setting, requiring reprogramming or overriding each weekend. For most people's schedules, this is less convenient than the other types because they require user input on a regular basis to see full benefit. As the cost of these units is not significantly less than models with more features, single-day thermostats are often less effective than other types.
Higher-end units adjust to the house's heating and cooling system, timing heating and cooling to achieve set temperature points at specific times. These features are known as adaptive or smart recovery systems.4 Smart recovery units are particularly desired for use with steam and radiant floor heating systems that have slow response times to temperature adjustments. Some thermostats have a hold/vacation feature, which allows for the programmed settings to be overridden for a short or long period of time. Habitual overriding of the efficiency settings, however, can lead to reduced energy savings. Low battery and air filter replacement indicators can also add to ease of use.
The United States' Federal Government ENERGY STAR program qualifies programmable thermostats that meet minimum performance criteria, including four temperature settings per day and an accuracy of 2 degrees.5 The ENERGY STAR program qualifies thermostats of all types listed above.
Programmable thermostats come in a range of features and price points. Prices range from under $25 to premium models as high as $150. A January 2001 Consumer Reports rating of available models gave high ratings to products at all price points. Programmable thermostats have a payback period from a few months to a year, depending on house size, insulation levels, and occupant schedules. Programmable thermostats have a simple payback of less then a year.
Thermostat Type Cost* Cost Premium Payback** non-programmable $20 --- --- basic programmable $25 $5 < 2 months 5-2 day programmable $50 $30 2 months 5-1-1 day programmable $80 $60 4 months 7 day programmable $100 $80 5 months
* Average cost of thermostats based on a survey of thermostats available at Home Depot, July 2008.
** ENERGY STAR estimates an average savings of $180/yr with a properly programmed thermostat
"EERE's Consumer Guide: Thermostats and Control Systems." U.S. DOE - Office of Energy Efficiency and Renewable Energy web site. 11 May 2008. U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy. 7 Jul. 2008. www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12720.
4 "Proper Use Guidelines for Programmable Thermostats." ENERGY STAR Web site. U.S. Environmental Protection Agency and U.S. Department of Energy. 7 Jul. 2008. www.energystar.gov/index.cfm?c=thermostats.pr_thermostats_guidelines.
5 "Which Programmable Thermostat is Best for Me?" ENERGY STAR Web site. U.S. Environmental Protection Agency and U.S. Department of Energy. 7 Jul. 2008. www.energystar.gov/index.cfm?c=thermostats.pr_thermostats_features.