According to a rough rule
of thumb, energy savings are 1% of the total heating bill for each degree of
setback for an eight-hour period. For homes with central cooling, similar
savings are possible for thermostat "setups." Actual savings will
depend on your current heating bill, and the specific setback program you
select. Switching to automatic thermostats from manual thermostats can save a
great deal if you can't guarantee consistent manual operation. The benefits of
control freedom and waking or returning to a just heated home may alone be
worth the price.
Automatic
Thermostats
Automatic thermostats may be grouped by type of control system: clock or
programmable.
Clock thermostat
Appearing first on the market, this type of automatic thermostat is
now considered relatively limited compared to its programmable successors. A
clock dial is physically arranged so that heating occurs only at preset hours.
Although up to three setback periods may be available, the setback amount (in
degrees temperature) is fixed. Setback periods are often limited to multiples
of one hour. Variations of the clock thermostat include one that will
automatically setback until a button is touched reactivating the heating
system for a preselected time period of 1/2 to 12 hours. Although less
expensive than other clock thermostats this unit is not truly automatic and
will not heat the home without user input. The least expensive alternative is
a thermostat heater mounted below an existing thermostat that during the
setback mode warms and "tells" the thermostat not to deliver heat.
Costs are generally in the range of $40 to $80.
Programmable
thermostat
Modern programmable thermostats use microprocessor circuitry for increased
information storage and control functions. Up to six different timed
temperature settings are commonly available with one-minute clock settings and
one degree setback accuracy. In addition, weekdays and weekends, and in some
cases even individual days, can be programmed separately. Thus, you can
"fine tune" your heating output and benefit from increased energy
savings and convenience. Many programmables provide an override function,
allowing temporary raising or lowering of the thermostat setting without
changing the program. Most also allow locking in the setback temperature when
away from home for an extended time. Some thermostats come
"pre-programmed" with setback periods, requiring only temperature
settings to be entered. Typically, when such pre-programming cannot be altered
by typical multi-step custom programming, the thermostat offers a choice among
various pre-programs. Another feature worth considering is the ability to
program the thermostat before wall connection to ease the learning process.
Costs vary widely depending on the number of control features included but
most fall in the range of $40 to $120.
Advanced options
On more advanced programmable thermostats, additional control options
are available. These can raise thermostat costs considerably, as much as $300.
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Control monitors can
keep track of the heating system's running time on a daily and weekly
basis. This information is useful in comparing the effectiveness of
various setback programs.
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Anticipators can turn
on the heat a set number of minutes before needed and turn off the heat a
set number of degrees before temperature is reached to prevent
overheating.
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Compensating
thermostats monitor heating times as a function of house temperature and
adjust the turn on (anticipation) time accordingly. Temperature feedback
is important for thermostats controlling heat pumps since it is
advantageous to bring the house to temperature slowly without requiring
the use of expensive backup resistant heating. This is often called ramped
recovery.
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Thermostats that
control more than one heating system are referred to as multi-stage or
dual-fuel systems. In the air conditioning mode, certain thermostats are
able to minimize short on-and-off cycling, and control fans for highest
efficiency.
Installation
Thermostat installation by the homeowner is often suggested by the
manufacturer. Contractors charge about $25 to $75. The critical concern is
compatibility of the thermostat with the heating and cooling systems. Most
thermostats are designed for only a limited number of systems and typically
take power from a 24-volt AC furnace control circuit. Many will not work with
heat pumps, millivolt systems (certain gas heaters) and 120-volt AC systems.
Check for compatibility prior to purchase by examining the thermostat's
instruction manual and wiring diagrams as well as one's existing thermostat
wiring. In case of power failure battery backup is common. Several thermostats
operate on battery power alone.
Selecting a
Thermostat
Other than compatibility, the most important consideration will be finding a
thermostat with options that best satisfy your particular needs. Proper
selection and installation can dramatically influence the amount of energy
savings, comfort, and convenience you receive from your investment.
