Thermostats

General Operation
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. This strategy is effective and inexpensive if you are willing to adjust the thermostat by hand and wake up in a chilly house. In the summer, you can follow the same strategy with central air conditioning, too, 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.

A common misconception associated with thermostats is that a 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. This misconception has been dispelled by years of research and numerous studies. The 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.

In the winter, significant savings can be obtained by manually or automatically reducing your thermostat’s temperature setting for as little as four hours per day. These savings can be attributed 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. The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates.

In the summer, you can achieve similar savings by keeping the indoor temperature a bit higher when you’re away than you do when you’re at home.  That is “a bit” higher.  Unlike a furnace an air conditioner will consume more energy if it is tasked with trying to quickly recover from a very warm interior space temperature, especially on a hot day.  A better strategy than turning the air conditioner off until it is unbearably hot, or using a programmable thermostat to start cooling at four or five in the afternoon, is to have a less aggressive setback temperature of perhaps 76 to 80 degrees while the space is unoccupied or to begin cooling an hour or two earlier in the afternoon.  It will also save energy to use a less demanding setpoint when the space is occupied during the hottest part of the day.  A space temperature of 76 degrees will feel very cool to most occupants on a 85 to 95 degree day.

There is a certain amount of inconvenience that results from manually controlling the temperature on your thermostat. This includes waking up in a cooler than normal house in the winter and possibly forgetting to adjust the thermostat (during any season) when you leave the house or go to bed.

Thermostats with Automatic Temperature Adjustment
To maximize your energy savings without sacrificing comfort, you can install an automatic setback or programmable thermostat. They adjust the temperature setting for you. While you might forget to turn down the heat before you leave for work in the morning, a programmable thermostat won’t! 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. The newest generation of residential thermostat technologies is based on microprocessors and thermistor sensors. 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.

Along with programmable thermostats, various types of occupancy sensing thermostats are also available that will default to more efficient settings when the space is unoccupied.  These include occupancy and light sensing stats.

Other Considerations

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.

Some modern heating and cooling systems require special controls. Heat pumps are the most common and usually require special setback thermostats. These thermostats typically use special algorithms to minimize the use of backup electric resistance heat systems. Electric resistance systems, such as electric baseboard heating, also require thermostats capable of directly controlling 120 volt or 240 volt line-voltage circuits. Only a few companies manufacture line-voltage setback thermostats.

A Simpler Way to Control Your Environment
The best thermostat for you will depend on your life style and comfort level in varying house temperatures. While automatic and programmable thermostats save energy, a manual unit can be equally effective if you diligently regulate its setting—and if you don’t mind a chilly house on winter mornings. If you decide to choose an automatic thermostat, you can set it to raise the temperature before you wake up and spare you some discomfort. It will also perform consistently and dependably to keep your house at comfortable temperatures during the summer heat, as well.