Hand holding up a Kill-A-Watt device.

Me and My Kill-A-Watt

Therese Peffer

Nearly thirty years ago, I bought my first solar panel—it provided 60 watts of power to the trailer I lived in while I was working and living off the grid for Home Power magazine (my first job out of college). The single panel cost over $400! At the time, solar was pretty expensive, but if you lived more than a quarter mile from the utility grid, it was cheaper than paying the utility to extend the power line. So before anyone even considered installing a solar photovoltaic (PV) system, you made a list of your electric appliances and tried to make your home as energy-efficient as possible.

Using the Kill-A-Watt

How does the Kill-A-Watt work? You can unplug any electronic device from a typical 120VAC outlet, plug in the Kill-A-Watt meter, then plug in the device to see how much power it consumes. You can leave the meter on for a day or so to track average energy consumption, but I thought I would try it out—just looking at instantaneous power—to see what I could learn about my own appliances.

I found the meter to be a little confusing: it has a lot of features, and I really wish it had a backlight to see the numbers on the screen (which was too dark and the text was too small to read). You can see real-time voltage (V), frequency (Hz), and if you leave a device plugged in for a while, energy consumption over time (hence the Reset button to reset the recorded data). You can also add your utility cost per kilowatt-hour (kWh) to see how much the energy needed to run the appliance costs over time.

Monitoring Power

First, I plugged in an air filter/fan/heater device. I pushed the up/down buttons on the Kill-A-Watt meter to toggle through the various choices and see the power reading in watts (W). I set the fan to level 10 and saw the meter recorded 24.7 W; lowering the fan to level 4 gave a reading of 7.4 W. I briefly turned on the heat and saw the reading soar to over 1400 W. Turning off the fan with the switch (but leaving it plugged in) showed 1.4 W.

This surprised me since the fan doesn’t have a light or display “on” when it is turned off. The energy consumption when a device is turned off but still plugged in is called standby power (or a phantom or vampire load). A professor here at UC Berkeley says our goal should be “doing nothing well”: we want to make sure we don’t consume energy when electrical services aren’t available. Now, 1.4 W doesn’t sound like much, but when a device is on for 24 hours a day, 365 days per year, it will cost about $4/year. I plugged in a few more devices and recorded the power consumption (see table below):

  • Office equipment: I was surprised by the modem and Wi-Fi router: 20 W! My son left his laptop and phone plugged in even though he is away for a week: 11-12 W.
  • Kitchen: A few years ago, my family’s microwave oven died, and my brother-in-law gave us his older microwave, which has a turn dial (no push buttons and no clock display—I love it!) I didn’t expect the microwave to have any standby power; our electric kettle is also pretty simple. Sure enough, there wasn’t any energy consumption when these devices are turned off.
  • Refrigerator: This Kill-A-Watt exercise gave me incentive to finally pull out the refrigerator. I’m embarrassed to admit I haven’t vacuumed the back vent of the refrigerator for a couple years, so I decided to measure the energy consumption before and after cleaning. The refrigerator consumed about 123-124 W before vacuuming the dust and 120 W afterward! That will save about $3/year.
DevicePower consumption (W)Standby (W)
Dyson air filter/fan/heater7.4-24.7 (level 4, level 10 speed); 1300-1400 W for heat)1.4 W
Modem/Wi-Fi router/Flume Wi-Fi bridge20 WN/A
Printer11.5 W when printing5.5 W
Laptop40-53 W20 W with a fully charged battery
Desktop computer & 19” monitor80-100 W4.4 W
Instant Pot1,000 W0.4-0.5 W
Microwave (no clock)1,000 W0 W
Electric kettle8000 W
Refrigerator123-124 W; 120 W after vacuuming!N/A
Fully charged laptops & phoneN/A11-12 W
The power consumption of several household electronics. Credit: Therese Peffer

Lessons Learned

What do I do with this information? I should definitely unplug devices when I’m not using them, such as the fan and Instant Pot. Some devices are harder to unplug and plug back in because the outlet is behind a desk or couch. For example, we don’t use the printer very often, so a 5.5 W standby load is pretty obnoxious (costing about $16/year.). I located a switched plug strip next to the printer so we can easily turn it on when needed. We can also unplug the laptops.

For loads such as the modem and computers, I can get a smart power strip or outlet that can be scheduled to turn off at night (say from 11 pm to 6 am) to reduce the standby load. That should save about $40/year—enough to pay for the smart plug strips!

If you have any questions about using the Kill-A-Watt meter, please let me know at tpeffer@berkeley.edu. I guarantee you’ll learn more about energy!

Cover image: Flinn Scientific

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