What Stays On When You Go Out
The lights are out, nobody is home, but the electric
meter is running.
"We were away for a whole month and our utility bill
barely dropped." This comment (or some variant) is heard at
the end of the summer in millions of households. For reasons
which often remain mysterious, utility bills scarcely change
even when the house is empty for most of the billing period.
Here are some explanations of why the utility bill stubbornly
clings to occupied levels during vacant periods. And, of course,
Home Energy suggests ways to reduce the vacation utility
The Modern House
The modern house is increasingly equipped with appliances
that consume energy without any active intervention by the
occupants. Most of the time, these appliances are considered
the benefits of civilization. We get hot water with the
turn of a faucet, ice cream from the refrigerator, and so
on. The trouble is, many of these benefits continue to be
available even when the occupants are not around to enjoy
them. And that wastes a lot of energy. The list of appliances
in the "set and forget" category is surprisingly long. Table
1 lists some of them. Keep in mind that energy use differs
in summer and winter.
Saving Energy During Vacations: The Dilemma
Simply pulling the plug on the guzzling appliances is not
always a reasonable solution. For many, there is an inconvenience
in disconnecting or reconnecting appliances (Oh Golly! How
do I reprogram the VCR?). Water beds, for example, take
days to regain their operating temperature. Many weary travelers
look forward to a hot bath the moment they return home;
a two-hour wait for the water heater to recover may be unendurable.
There are also potential health and safety hazards, like
spoiled food or burst water pipes. These factors need to
be balanced against the savings in reduced bills. The longer
the vacation, the more disconnect-reconnect inconvenience
Much of the consternation about vacations and utility bills
can be traced to the refrigerator--the largest user of electricity
(in both vacant and occupied homes). Less than 20% of a
refrigerator's energy use is due to door opening, food loading,
and other occupant-caused effects. Refrigerators are also
very sensitive to the temperature of the kitchen. A buttoned-up
house will raise the kitchen temperature and can increase
the refrigerator's energy use 50% during the summer. It's
worse if there's a second refrigerator or freezer purring
in the basement or garage. Depending on the refrigerator's
efficiency, assume 40-150 kWh per month.
It is tempting to simply unplug the refrigerator. This
is unwise, especially in humid climates. Even in an empty
refrigerator, tenacious and smelly mildew and mold will
form within days. If food remains in the refrigerator, there
are few options to leaving it at the normal settings.
If it is possible to completely empty the refrigerator,
the thermostat should be set to the lowest possible temperature.
With luck, the refrigerator will use 40% less electricity.
Heating and Cooling
Millions of households have discovered the ease of saving
energy (and increasing comfort) with automatic thermostats.
However, these wonderful devices are often a nuisance to
reprogram--or are simply forgotten in the rush to leave--so
they obediently heat or cool empty homes. Their contribution
to a utility bill is impossible to estimate because it depends
on the climate, the house, and the extent of the setback
(or set-up for air conditioning). If the vacation is in
the midst of a summer heat wave or a January cold spell,
the automatic thermostat can generate a nasty surprise on
the next utility bill.
The solution is unpleasant: learning to reprogram the thermostat.
This is a task that should be done long before the departure
hour and checked carefully. An incorrectly programmed thermostat
can be a disaster. Some thermostats have special vacation
settings that (once programmed) simply require a flick of
the switch. Others take more effort ... a lot more effort.
It's best to chose temperatures that maintain a safe environment
in the house. In areas with extreme cold, this means avoiding
frozen pipes. In hot climates, high indoor temperatures
may create other hazards particular to the climate and contents
of the house. Think first, and perhaps consult the local
Central thermostats don't control all space conditioning;
many homes have extra heaters or coolers that serve a remote
corner of the home. It is an easy matter to overlook gutter
heaters, strip heaters, and other little heaters.
On the cooling side, the dehumidifier (which is present
in a large fraction of houses in the Midwest) operates almost
independently from the air conditioning system. A dehumidifier
can consume up to 20 kWh per month during the summer, and
can therefore be a contributor to the vacation utility bill.
The dehumidifier should be turned off during vacations if
it doesn't have a permanent water drain. If the home has
a serious humidity problem, it may be necessary to operate
it while the occupants are away.
Heat pumps have a particularly insidious vacation consumption.
Even when the thermostat turns off the heat pump, a "crankcase
heater" continues to heat the refrigerant and lubricant.
New units have thermostatic controls on the heater but many
still draw a steady 30 W or 20 kWh per month. The crankcase
heater can only be turned off by switching off the heat
pump at the circuit breaker or disconnect switch. At restart,
a couple hours must be allowed for the crankcase heater
to reheat the refrigerant-lubricant mixture before operating
the heat pump or the compressor may be damaged.
There are also lots of furnace pilot lights still burning.
Switch them off for a summer vacation and the savings will
probably continue until the heating season begins. Save
4-6 therms per month, possibly for a few months.
Water heaters are a simple target for vacation shut-down.
They use a lot of energy (3-8 therms per month or 50-150
kWh per month) just keeping the water in the tank hot. For
gas water heaters, the simplest option is to switch the
unit to "pilot." By leaving the pilot switched on, less
energy is saved, but it's much easier procedure to switch
back to "burner" and restore normal service. (The pilot
will keep the water plenty warm anyway if the tank is well-insulated.)
This measure can easily save several therms per month.
Electric water heaters are trickier to switch off. It may
be necessary to do it from the circuit breaker box. Just
rotating the dial to the lowest possible temperature setting
(some units even have a "vacation" setting) can save more
than 25 kWh per month.
Some newer kitchens have "instant" hot water taps at the
sinks. These devices include a small hot water reservoir
under the sink and usually draw a constant 20 Watts. Unpluging
those water heaters before departure saves an easy 8-20
kWh per month.
Pumps appear in several residential appliances: pool pumps,
well pumps, and sump pumps. Most have some sort of control
to decide when it is necessary for them to operate. This
may be a float, clock, pressure switch, or other sensor.
It's not wise to interfere with these controls unless their
functions are completely understood. However, it is possible
to limit the demand for the service and therefore reduce
operation. A swimming pool pump can be put on reduced hours
when the pool is not being used. (Even greater reductions
are justified if the pool is covered.) This can easily translate
into savings of almost 100 kWh per month. Well pumps should
probably stay switched on, but eliminating water leaks will
prevent unnecessary cycling. This means fixing leaky faucets,
toilet valves, and so forth.
Lights rate relatively low on the scale of vacation guzzlers
for two reasons. First, lights are visible, so people generally
remember to switch them off. Second, lights don't use as
much electricity as other appliances. An exception is large
collections of clock or photocell-controlled exterior flood
lights; their consumption can be significant, up to 30 kWh
per month for each flood lamp. Instead of leaving any lights
on all the time, connecting them to a timer, photocell,
or motion sensor (or a combination) saves energy. Such clever
controls can deliver an 80% reduction in lighting energy
use. If internal lights must be kept on while the occupants
are absent, a compact fluorescent lamp is a worthy choice.
It can reduce lighting energy use by 60%.
The Gas Stove
Old gas stoves can have up to four small pilots heating
up an empty kitchen. They are easy to turn off, but often
a nuisance to relight. Some have valves near the flames,
but many require depressing an override button (which is
always inconveniently located) for 60 seconds. A compromise
is shutting off the range pilots but leaving the oven-broiler
on. New gas stoves don't have any pilots, so they are one
less appliance to worry about.
Many electronic devices draw a small, constant amount of
power. One device alone is almost undetectable; however,
when multiplied by ten or more, the load becomes noticeable
and even a little annoying. There is no single villain that
stands out; instead there are little things scattered around
the house. For some, it's definitely worth pulling the plug
while gone; others are a nuisance to reprogram. One nearly
invisible draw is the instant-on feature on the television
(5-40 W). If the TV is unplugged, it's really off. Cable
TV converter boxes shouldn't be left plugged in either;
some draw as much as 30 W.
Most houses are now littered with little black transformer
cubes attached to the outlets that convert 115 V alternating
current to direct current for various electronic equipment,
from cordless phones and "dustbusters" to battery chargers.
Modern middle-class homes can easily have ten of these transformers.
Each of these draws 1-5 W, even when the appliance is switched
Then there are the clocks and miscellaneous devices. Each
draws a few watts (more if illuminated). Again, they are
individually small but noticeable in a house equipped with
a dozen clocks. At the very bottom of the list are the ground-fault
interrupter (GFI) outlets. These outlets draw a trickle,
less than a watt. New homes may have GFIs in the kitchen,
the bathrooms, outdoors, and garage, together drawing 10
W or less than a kWh per month--peanuts--but enough to keep
the meter turning.
Don't Forget the Fish
Pets and plants are major energy guzzlers. At least 8%
of U.S. homes have aquariums and most of those lights and
heaters. A reasonably equipped aquarium can easily consume
10-150 kWh per month. Unless the fish go on vacation, too,
this consumption won't disappear when the people do. Other
pets get special treatment, from heated water dishes to
bed warmers. If the pet goes to a pet sitter, make sure
that these get unplugged.
Exotic plants and flowers grow under special lights that
usually operate even when the "farmers" are absent. A small
horticultural installation can draw 10-50 kWh per month
in lighting alone. If the contents are valuable, don't even
consider pulling the plug on these herbariums, terrariums,
Avoid a Surprise Bill
It is easy to see how a vacant home can operate on "automatic
pilot" and consume nearly as much as when occupied. All
together, the refrigerator and a few other appliances can
consume a couple hundred kilowatt-hours, and produce an
unpleasantly high vacation utility bill. Many of the conservation
measures described above save at most a few dollars each.
But when combined, they make a significant dent in the bill.
Even greater savings might be achieved through a total
shutdown, but this can be accomplished only if the person
shutting down the house thoroughly understands the house
and the implications of suspending each energy use. Nevertheless,
spending 30 minutes shutting down a home may be worthwhile,
especially if attacked methodically and intelligently. Compromises
are also possible. If somebody is mowing the grass or collecting
the mail, she can also be hired to switch on the crucial
items on the day before return. The most important thing
to realize is that energy consumption doesn't stop just
because the occupants are away. n
The `Set and Forget' List
ELECTRICITY Typical monthly consumption
Appliance or user (kWh/month)
Electronic gadgets with transformers
Battery charger 2-4
Cable TV box 5-20
Computer modem 2-4
Cordless phone 2-4
Cordless vacuum 2-4
Telephone answering machine 2-4
Auto Engine block heater1
Automatic defrost 120-140
Manual defrost 60-80
Garage door opener 1-4
Ground fault interupter outlets (5) 4
Gutter and pipe heater tape1
Heat pump crankcase heater 20
Inside "evening" light 10-30
Night "security" light 80-120
Fax machine 2-8
Television and video2 4-20
Standby loss 50-150
In-sink heater 8-20
GAS Typical monthly consumption
Appliance or user (therms/month)
Furnace pilot 4-6
Stove pilots 2-6
Standby loss 3-8
1. Highly sensitive to house and local conditions
2. Assumes vacant home and no use