Building your Energy Savings Toolbox – Kill-a-Watt meter

The Kill-a-Watt meter, made by P3 International, will tell you how much electricity (power in Watts) a given device is using at that moment and how much energy (kWh) it consumes over time.
The Kill-a-Watt measures the electricity used by devices that plug into the wall, often referred to as the plug-load.  Items like your refrigerator, toaster, and cell phone chargers are all plug-loads.  Room lighting that you control from the switch on the wall is hard wired (that is not a plug-load) so you cannot measure these with a Kill-a-Watt.  Fancier meters are available that will tell you the same things in more detail, but they are more expensive and the added accuracy does not help for general understandings.

The basic P4400 is my favorite one because it is inexpensive (under $20) and simple to use.
How to Use a Kill-A-Watt
Depending on how the device you are testing works, there are two ways to measure its energy usage.

1. Calculate It – If the device is either on or off, like a toaster, then you cansimply measure the power it uses by pressing the Watt/VA button.  Make sure it is showing you W, if not press the button again.  You can then estimate how many hours it will be on for a given period of time and calculate the energy usage (kWh) by multiplying times the power (W) and dividing by 1,000.
2. Track It – If the device cycles (turns on and off over time) or is variable, like a refrigerator, you will need to plug the Kill-a-Watt in for a day or two and measure the energy used over time.  Push the KWH/Hour button to see how many kWh of energy was used since it was plugged in to the wall.  Press the KWH/Hour button again to see how many hours it was monitoring the device.  You can then estimate how many kWh that device will use in a given period of time.

Now answer the questions above.  If the device uses a lot of power when off or not in use, consider unplugging it or putting it on a powerstrip with other such devices and switching off the powerstrip when you don’t need it.  If the device uses a lot of electricity when on, consider turning it off (or to a low power mode) whenever you are not using it.  This is especially true for computers, check out our article Sleep your PC to Save Energy for more advice on managing computers.  If you find that the device is an energy hog, uses a lot of energy (kWh), for example, that old second refrigerator, then consider upgrading that appliance with an Energy Star model or figuring out if you really need it.

Keep a list of the devices you measure and compare them with your overall monthly energy bill.  You may be surprised to learn what your biggest energy hogs are.  The unexpected device for me was our cable box which uses about 40W even when “turned off.”  We’ve put it on a powerstrip and leave it off most of the time.

Ask to borrow before buying a Kill-a-Watt
Unless you want to own one to loan to friends and family, try borrowing one first.  Check with your local library as some of them actually check out kill-a-watts like books.  Ask your friends, you’d be surprised at how many folks have a Kill-a-Watt, and it could start a great conversation about saving energy and living greener.

I have not seen them in a brick and mortar store yet, and have been looking for years now.  I recommend ordering online through EFI or Amazon.com (affiliate link) .  The one complaint I have about the P4400 is that when you plug it into an outlet, it covers up all of the outlets.  A $0.99 6″ cord extension, available from most computer stores, easily solves that problem.

P3 International makes several versions of the Kill-a-Watt built into powerstrips and the newer P4460 (EZ) has a battery so that it can store some things even through a power outage.  I don’t think it is worth the extra $20.  The P4400 does lose the data when it is unplugged, so be sure to record your measurements before testing the next device.

Happy Greening!
Jon