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How to Measure Home Power Usage

Electricity costs money. Devices can help you save, especially by killing vampire energy leaks... if you know what they do and how to understand your bills.

Terms to Know (AKA The Boring Measurement Stuff)

When you're looking at your electricity bill, you're bombarded with a lot terms and abbreviations that seem pretty meaningless. Worse, they'll vary from country to country, because the United States can't ever agree to a standard used by most other locations. For this outing, I'm talking mainly about the terms used in the US—specifically the Kilowatt Hour.

The Kilowatt Hour (kWh, sometimes styled as "kW h" or "kW-h", but NEVER "kW/h") measures energy. It is about how much fuel is in something or how much energy is used over a certain time period. It's like a calorie or joule—they're all different ways to measure energy. For example, 172 Calories (technically kilocalories) is about 0.2 kWh. It's how we know the food we eat gives us energy, just as electrical power gives lights energy. It's possible that burning up food could power a light (if done exactly right)—that's why there are a lot of ways to measure energy. But while kWh implies a time period of use, technically, it's not. It's actually the "equivalent to one kilowatt (1 kW) of power sustained for one hour," according to Wikipedia. Yeah, whatever.

The Kilowatt (kW) measures power. It looks at how fast something is being used up. The more Kilowatts used, the more energy "burned." A kilowatt is 1,000 watts; one watt is the same as one Joule per second (J/s). Which is confusing, since J/s mentions a time frame (second) but it doesn't compare to kWh (which mentions hours, but isn't about time). Isn't science great?

What you really need to know: if a device is rated to generate 1 kW of power, and if it operates for one hour at that level, it sustains 1 kWh of energy. A device using 100 watts over 10 hours would utilize 1kWh of energy (100x10=1,000=1kW). The Wikipedia example: a 40-watt bulb, used for 25 hours (40x25=1,000 watts = 1 kW) would also be using 1 kWh (even though it took 25 hours to get there).

The kWh is how most home energy costs are calculated. You typically get charged a set few cents per kWh. So if it's $0.25 per kWh, that 40-watt (0.04 kW) bulb used for 25 hours (1 kWh) costs you a quarter. If only it was that simple.

My own bill from the central New York utility NYSEG lists, under Delivery charges, a basic flat service fee, then a number of fees that went toward paying the 786 kWh listed for me from Feb. 12 to March 9. That included a delivery charge, a transition charge ("the cost of making the electricity...industry more competitive"), revenue decoupling mech ("difference between forecast and actual deliver service revenues"), reliability support services charge ("cost incurred...for third-party services to ensure local electrical reliability needs are met"), and a New York state assessment required by law since 2009. Then there's something called SBC/RPS charges, used to fund clean energy efficiency programs, which differ from February to March. Sheesh. And those are just delivery.

There are more charges for the actual electricity supply, then taxes and surcharges from the county as well. The total for me to use those 786 kWh: $84.07. These are typically lean months for my admittedly high electrical household use since our heat is natural gas-based. Electricity use here spikes in August with air conditioner season.

So it would be nice to know what to unplug and turn off more often to get the price down.

Tools You Need to Stake Vamp Energy

Measuring your household kWh use is as simple as comparing bills every month—but that won't help you isolate which devices or appliances are killing your bill. Plus, it won't really tell you anything about devices that make slow yet lengthy draws on the juice from the local electric utility.

You can make a pretty good guess using the Energy Vampire Calculator from Duke Energy; put in a guess on how may PCs, chargers, TVs, monitors, printers, etc. you have plugged in full time, and it'll spit out a guess of how much you're wasting.

To get specifics regarding your energy usage, you only need one tool, really: an electricity usage monitor that tells you exactly how many kWh a particular device or appliance is drawing. The monitor can be as simple as a $14 "plug load" monitor that plugs into an outlet; then you plug the device/appliance into the monitor. Typically, an LED screen shows you the consumption.

One of the simplest, least expensive, and best known of the plug-l

​​oad variety is the P3 Kill A Watt EZ, available at Amazon and big box stores like Home Depot. After it pulls for a while, push some buttons to have it auto-calculate how many kWh will be used in a day, week, month, or year, so you have an instant estimate. It also measures the quality of your line. It's for use on 110 to 120 volt systems—115V is nominal—not 220V and 230V like you'll find almost everywhere else on Earth, nor is it for electrical dryers and some hot tubs and other specialty appliances.

More advanced versions, like the Kill A Watt Control, not only monitor, but can be set with programs to turn on and off to save electricity on your pre-set schedule. It has backup batteries so if you disconnect it from the outlet, it'll hold all the info it's already recorded.

If you're into having a smart home, the Digi XBee Smart Meter combines consumption monitoring into a ZigBee-powered smart outlet. So you can control it—remotely turn off lights, etc.—while it also measures kWh on the outlet. It costs about $84. P3 is also in the game with a new Kill-A-Watt Wireless Monitor and Sensor, but be sure to get each—only one of them is useless. But really the top choice here is to get a product that also doubles as a home automation smart-outlet you that you control with a hub or your smartphone; the Belkin WeMo Insight Switch, our PCMag Editors' Choice, fits the bill perfectly, as it'll also monitor usage.

If you want whole-house monitoring tools, there are several systems that work with sensors on the lines that talk wirelessly to meters and gather lots of data. Many should be installed by an electrician. The Ted Energy Detective Pro Kit is an example of one you can install yourself if you're brave around main electrical lines—it goes for about $300 (and now works with Amazon's Alexa); Neurio's Home Electricity Monitor for $218 is similar, with wireless sensors installed at your home's electrical box. That's probably more advanced than you need. However, at least one, the Blue Line Innovations PowerCost Monitor(below), has a single sensor you attach right to your house's electrical meter to get a wireless measure—even on your smartphone—on what's coming in. None of them will help you pinpoint a power-sucker in the home—for that you need to use plug-load monitors and move them around from device to device to check them.

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