The Project

Kill-a-Watt Power Meter

Ever wonder how much electricity all of those different household appliances use? The results might surprise you. For about $20 you can get the P3 Kill-A-Watt power meter and see what's using all those kilowatt-hours.

Kill-A-Watt meterA Kill-A-Watt power usage monitor plugs directly into the outlet. You then plug in any electrical appliance and find out how much power you're using. The electricity is measured as it passes though the Kill-A-Watt meter. The meter tells you how much electricity is used over a certain time by the appliance (it also calculates how many kilowatts are used per hour).

In my state, a kilowatt hour (KWH) costs about 10 cents at the time or writing. Check your own state.

So what kinds of things can you learn from using the Kill-A-Watt meter?

Refrigerator Refrigerator
Time tested: 168hrs
KWH used: 24.5
One of the biggest users of electricity in the home, especially if it's made before 1993. Check that fridge in the garage—it could be costing you $100 or $200 a year. We tested our fridge for a week in February and calculated it was using 1280 KWH a year. Our new one uses 438 KWH per year. See a graph of our monthly electricity bill before and after.
Stereo System Stereo System
Time tested: 69.55 hrs
KWH used: 2.05
When your stereo system, DVD player, and speaker are plugged in they are still using energy even when they're turned off. We tested our home entertainment system and estimated that we're spending 7.25 cents a day or 26.52 dollars a year.
Computer Computer
Time tested: 94 hrs
KWH used: 0.86
In my workroom downstairs was an old computer I used a few times a year to scan slides. By leaving it plugged in it was costing me over two cents a day or $8.25 a year.
Power Supply Power Supply
Time tested:114 hrs
KWH used:0.12kwh
An ordinary power supply uses power even if it's not plugged into the device. I tested the power supply for my Garmin GPS unit and found it uses about one cent every four days. That's only 91 cents a year but the little things do add up.
Cordless Phone Cordless phone
Time tested:72 hrs
KWH used: 0.15
Cordless phones are convenient but how much electricity do they use? Mine costs one cent every two days or $1.87 a year.
Microwave Microwave Tea
Time tested: 4.0 min
KWH used:0.06
(time averaged over five trials) Heating a cup of tea in the microwave costs a little over half a cent.

The Kill-A-Watt meter is available for under $25 and can be found by searching Google.