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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 bill.

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 is justified.


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 utility.

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 Heating

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.

Electronic Gizmos

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 off.

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, or greenhouses.

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)
Aquarium                                                     10-150
Clock                                                           2-5
Dehumidifier                                                   5-20
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
Greenhouse                                                    10-50
Gutter and pipe heater tape1
     Heat pump crankcase heater                                  20
     Inside "evening" light                                   10-30
     Night "security" light                                  80-120
Office equipment
     Computer                                                   2-5
     Fax machine                                                2-8
     Pool2                                                    5-200
     Sump                                                      1-10
     Well2                                                     0-20
     Guzzler                                                150-200
     Miser                                                    40-60
Television and video2                                          4-20
Waterbed                                                     50-200
Water heating     
     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
Water heater     
     Standby loss                                               3-8
1. Highly sensitive to house and local conditions
2. Assumes vacant home and no use
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