Thermostats

Energy and money savings can be substantial in the winter by turning down your thermostat. In the upper Midwest, for example, setting back the temperature from 68 to 55 at night can save at least $10 to $20 a month on fuel. You will achieve such savings with any thermostat--if you remember to set and reset it daily; or you can use an automatic setback thermostat. A setback thermostat offers comfort and convenience since it can turn the heat on before you get out of bed or raise the temperature before you come home in the evening. A setback thermostat also offers dependability since it will automatically change the temperature day in and day out. There are two types of setback thermostat. Digital electronic models offer the greatest number of temperature settings and setback periods, but are complex. Electromechanical thermostats are easier to set but have fewer features and less flexibility.

These descriptions and recommendations do NOT apply to heat pumps unless a special heat pump thermostat is used. Refer to the section on Heat Pumps.

Thermostat makers routinely offer dozens of variations on a given model, to make the thermostat compatible with different central heating systems, central air-conditioners, or both. They are designed for do-it-yourself installation.

Basic Operation

The typical electronic thermostat can provide two energy-saving periods each day. For example, on Monday through Friday, the thermostat can raise the household temperature to 68 from 7 to 9 a.m.; drop it to 60 during the day; raise it to 68 from 5 to 11 p.m.; and then drop it to 58 for the rest of the night. On Saturdays and Sundays, the thermostat might be set to keep the household temperature at 68 throughout the day.

The most versatile setback thermostats allow different comfort and setback periods for each day of the week. You can override the settings at any time; for example, to keep the temperature low if you will be out of the house in the early evening.

Any thermostat, even a digital electronic model, is essentially an on/off switch. When it senses that the room temperature has dropped too much, it signals the furnace to provide heat until the temperature rises sufficiently. In use, the thermostat will let the room's temperature rise or fall around the temperature you have set, in part to avoid subjecting the furnace to rapid on-off cycles.

The electromechanical thermostats depend upon the expansion or contraction of a metal coil to physically move a small mercury switch that turns the furnace on or off. An electronic thermostat uses more elaborate sensors and microchips instead of the mechanical devices.

Temperature Swings

Location of the thermostat is crucial to the effective and efficient operation of the heating and cooling system. It is important to place the thermostat in a central location (not near supply registers or other heating or cooling sources) in order to give an average temperature reading.

Any good thermostat should keep a room's temperature fairly constant without letting the temperature vary more than a few degrees. A good thermostat should also be easy to program (or reprogram) and give plenty of options for setting time and temperature.

You can expect a thermostat to hold closely to the setting you have chosen, but not necessarily expect that reading to be absolutely accurate.

Keeping Cool

Most thermostats let you enter completely independent programs for heating and cooling. Others let you store only separate temperature settings. You must keep the same time periods for heating and cooling, or reprogram the periods at the end of the heating or cooling season.

Air-conditioners are also cycled on and off two to four times an hour by the thermostat which keeps the temperature swing to about three degrees or less. Humidity is another factor controlled by the thermostat in the conditioned space. Sometimes it is more important to keep the humidity relatively low than it is to have the energy savings from higher temperature settings.

Programming Ease

Electromechanical thermostats are the easiest to program. Under the cover of each is a clock-timer that holds moveable tabs similar to those on a household timer. The tabs are positioned to control the setback and comfort periods. As the clock-timer dial turns, the tabs trip a switch to change the setpoint. (Two tabs yield one comfort and one setback period; four tabs yield two comfort and setback periods.) Then the comfort and setback temperatures are set with levers. But that simplicity limits versatility. These thermostats allow only one comfort and setback temperature and their routine is necessarily the same every day of the week.

What You See

The display on a digital electronic thermostat can tell you the time of the day, the room temperature, the setpoint temperature, and more. But not all of the information available is useful or easy to access. You may have to refer to an instruction manual to determine how the display operates. Some thermostats may not even display the current set temperature.