Does leaving things plugged in waste electricity?

My daughter tells me I waste electricity by leaving things plugged in. She’s been doing an energy audit of her high school (for her science class) and seems to think she’s an expert in energy efficiency all of a sudden. I tried to tell her that it won’t make much difference to unplug everything in our house, but she insists that it’s wasteful to leave things plugged in, and she wanders around unplugging everything in sight that isn’t in use. Is she right or is she taking this too far?

Answer from Green Energy Efficient Homes

Electricity is a form of energy and in a sense all electricity does ‘work’. When you say an appliance might waste electricity what you really mean is that the work the appliance did with the electricity is wasteful. If the appliance doesn’t use any electricity, then there is no waste.

As I explain on my About me page, a number of years ago an engineer sold me a handy Kill A Watt to measure the power usage of plug-in devices, and I discovered that many of my household appliances were using small amounts of electricity continuously, while doing absolutely nothing of value for me. I consider ‘work’ to be something that is useful to me; having five digital time displays in one room isn’t really useful work!

What kinds of work typically waste electricity with plug-in appliances? Some obvious ones are appliances that produce light or heat without any benefit – for example, you might have an LED display on your DVD player or game console that stays lit up even when you aren’t using the device. That is needless work. Or you might feel heat from the AC to DC converter that powers an electronic device or charges the rechargeable dust buster. That heat is a byproduct of the energy conversion, and in and of itself it is wasteful because that heat is not helping power the device or charge the dust buster. If the converter stays warm even when the device it is supposed to charge is not plugged into it, then you’re wasting energy on the converter whenever it is plugged in, regardless of whether it’s charging or not.

So you do waste electricity keeping devices plugged in that consume electricity without doing any useful work. But if the plugged in device shows no sign of doing any work (useful or otherwise) there probably isn’t any savings to be had from unplugging it. For example, most modern USB-based cell phone chargers consume no electricity when no cell phone is plugged into them.

In some situations it’s obvious whether leaving something plugged in is wasteful. A simple table lamp that is left plugged in doesn’t waste electricity when the switch is turned off. An electronic device with an LED or other lit-up display is indeed using a tiny bit of electricity to power that display, and sometimes that also means it’s using a larger amount of energy for other purposes (for example, some TV screens have an instant-power-on feature that means the screen stays bright whenever you click the remote, and these instant-on screens can use up to 50 watts even when turned off, waiting for the on signal).

You probably won’t save the planet from climate change or slash your energy bill in half by unplugging appliances that aren’t using any (or much) electricity, but there are situations where you will waste less electricity by turning things off or pulling out the plug. For example, a television set with instant-on capabilities is using a small trickle of electricity continuously, waiting to receive your signal. If you can stand to wait 15 or 30 seconds each time you want to turn on the TV, then unplugging it when you’re done will save a little energy. Not enough to make a big dent in your electricity bill, but if each of us did things like this the cumulative effect on reducing energy use could be significant.

Another way to determine whether something left plugged in wastes electricity is to think what ‘plugged in’ means. For electricity to do work there has to be a closed circuit – a continuous two way connection between the power source (your local power plant, hydro dam, solar panel etc.) and the device doing the work. The table lamp that is plugged in allows electricity to reach the light bulb, but only if the light bulb switch is also turned on. The washing machine won’t work if unplugged, but it also doesn’t do any work if you haven’t turned the switch to the start position, which closes the circuit and starts the washing machine doing a load of laundry. So there’s no energy gain to be had from unplugging a washing machine. The same is true with most larger appliances such as dishwashers, dryers, toasters, toaster ovens etc., except that any of these that has a built-in digital clock or other display does use a small amount of power to run the display.

Again, you need to think in terms of ‘work’ being done. If no work is being done, there is no electricity being wasted. If work is being done, then there may be wasted electricity if the work being done is not of benefit.

Examples of work being done that isn’t useful include leaving a light on in an empty room (you should always turn off lights when you leave a room); leaving a cellphone or laptop plugged in when it’s fully charged; running the dishwasher when it’s not full; leaving that flashing 12:00 on the DVD player instead of unplugging it; and so on. In our own house we were able to significantly cut our electricity bill by measuring our energy consumption and disconnecting devices such as the chargers and routers and DVD player when not in use, but that was over a decade ago, and since then many of the devices that wasted electricity have been replaced, thanks to new regulations, by ones that draw no phantom power.

You may have heard elsewhere that you should unplug all AC to DC converters, and while I mention it here and have certainly benefited from this in my own house, you won’t necessarily save energy by unplugging every one of them. It’s true that any converter that feels warm or hot to the touch is wasting electricity – the converter may be using electricity even if the device it’s connected to is fully charged, or if there’s no device connected at the time. But most chargers can detect when there is no draw on the DC current portion of the circuit, and they will cut energy consumption of the converter to near zero, and I’ve certainly seen this on laptop chargers, which ten years ago would draw a steady 30-40 watt current even with no laptop plugged in; my current laptop charger doesn’t even register on my Kill A Watt meter when the laptop itself isn’t connected. Any device that has a charger or AC to DC converter and that is ENERGY STAR certified draws little or no power when the charger or converter is not plugged in.

I commend your daughter for trying to find ways to cut your home energy use, but you might want to remind her to use the same technique at home as she used at school: use the power meter she probably used for the school energy audit to measure the electricity consumption of home appliances, lights and the like, when they are turned off. She will quickly discover that at least some of the things she is telling you need to be unplugged, are not drawing any power at all, while others may only be drawing a watt or two – not really enough to make a differences to your electricity bill.