In our modern, high tech society, we don't think much about some of the
electronic gadgets in our homes. Take, for example, the ever present
thermostat--a staple of North American households for decades. It usually takes
the shape of an unassuming box on the wall, but that modest device controls
the comfort of your family on the coldest day in January and the hottest day
in July.
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, in its simplest form, must be manually adjusted to change the
indoor air temperature.
General Thermostat 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.
Another misconception is that 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. 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.
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.
But 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 thermostat 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.
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
cancelling 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.
Types of Automatic and Programmable Thermostats
There are five basic types of automatic and programmable thermostats:
- electromechanical
- digital
- hybrid
- occupancy
- light sensing
Most range in price from $30 to $100, except for occupancy and light
sensing thermostats, which cost around $200.
Electromechanical (EM) thermostats, usually the easiest devices to
operate, typically have manual controls such as movable tabs to set a rotary
timer and sliding levers for night and day temperature settings. These
thermostats work with most conventional heating and cooling systems, except
heat pumps. EM controls have limited flexibility and can store only the same
settings for each day, although at least one manufacturer has a model with
separate settings for each day of the week. EM thermostats are best suited
for people with regular schedules.
Digital thermostats are identified by their LED or LCD digital readout
and data entry pads or buttons. They offer the widest range of features and
flexibility, and digital thermostats can be used with most heating and
cooling systems. They provide precise temperature control, and they permit
custom scheduling. Programming some models can be fairly complicated; make
sure you are comfortable with the functions and operation of the thermostat
you choose. Remember-- you won't save energy if you don't set the controls
or you set them incorrectly. 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. Then, the temperature
returns to the setback level. These units offer the ultimate in simplicity,
but lack flexibility. Occupancy thermostats are best suited for spaces that
remain 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, a photocell
inside 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 units do not require batteries or programming and
reset themselves after power failures. Light sensing thermostats are
designed primarily for stores and offices where occupancy determines
lighting requirements, and therefore heating requirements.
Choosing a Programmable Thermostat
Because programmable thermostats are a relatively new technology, you
should learn as much as you can before selecting a unit. When shopping for a
thermostat, bring information with you about your current unit, including
the brand and model number. Also, ask these questions before buying a
thermostat:
- Does the unit's clock draw its power from the heating system's
low voltage electrical control circuit instead of a battery? If so, is the
clock disrupted when the furnace cycles on and off? Battery operated
backup 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.
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.
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.
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