Take Control of Your Electric Bill: How to Measure Home Power Usage

The modern home uses a lot of juice. Decades ago, electricity-hungry devices were mainly appliances, lights, the radio, and the TV. Today, it’s all that and so much more: energy-sucking PCs, charging phones, always-on routers, pool filters, security systems, surveillance cameras, baby monitors, and smart speakers, to name a few.

There may not be much you can do about the draw from each item you’ve got plugged in at home. You can at least contemplate saving some money, though, when you measure exactly how much electricity each device is using. But it takes some work to find all the so-called “vampire energy” being sucked away by devices in standby mode.

That’s right—even when you think something is turned off, it could still be using power, especially when the device is doing updates or talking to the internet. Finding those energy vampires can be worth your while. They cost Americans $19 billion per year as of 2015, according to an NRDC report(Opens in a new window), and we can safely assume things haven’t gotten better. But how do you put a stake in the heart of vampire energy?

Terms to Know (AKA the Boring Measurement Stuff)

When you’re looking at your electricity bill, you’re bombarded with a lot of 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 story, I’ll talk mainly about the terms used in the US—specifically, the kilowatt hour.

The kilowatt hour (kWh, sometimes styled “kW h” or “kW-h” but never “kW/h”) measures energy. It is about how much fuel is contained within something or how much energy is used over a certain time period. It’s similar to a calorie or joule, which are other ways to measure energy. For example, 172 calories (technically, kilocalories) is about 0.2 kWh. It’s how we know the food we eat provides us with 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.

While kWh implies a time period of energy usage, it’s actually the “equivalent to one kilowatt (1 kW) of power sustained for one hour,” according to Wikipedia(Opens in a new window). Yeah, whatever.

The kilowatt (kW) itself measures power: specifically, 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). This is confusing, since J/s mentions a time frame (second) but doesn’t compare with 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 use 1 kW of power, and if it operates for one hour at that level, it sustains 1kWh of energy. A device using 100 watts over 10 hours would utilize 1 kWh of energy (because 100×10 = 1,000 = 1kW). The Wikipedia example: a 40-watt bulb used for 25 hours (40×25 = 1,000 watts = 1 kW) would use 1 kWh (even though it took 25 hours to get there).

The kWh is how most home energy costs are calculated. You’re typically charged a few cents per kWh. So if the cost is $0.25 per kWh, that 40-watt (0.04 kW) bulb used for 25 hours (1 kWh) costs you a quarter. Right?

If only it were that simple.

(Credit: Eric Griffith)

One of my bills, above, from the central New York utility NYSEG, lists under “Electricity Delivery Charges” a basic flat service fee, then a number of fees that went toward paying for the 786 kWh listed for me from February 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 delivery 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. There’s also something called “SBC/RPS charges,” used to fund clean energy-efficiency programs, which differ from February to March.

Those are just delivery fees. The bill lists more charges for the actual electricity supply, then taxes and surcharges from the county. The total cost for me to use 786 kWh was $84.07. These are typically lean months for my admittedly high-electrical-use household, since our heat is natural gas–based. Electricity use where I live spikes up in July and August; that’s air-conditioner season.

Anyway, that’s an expensive way of proving that it would be nice to know what to unplug and turn off more often to get the utility cost price down.

Measuring household kWh use is as simple as comparing bills every month, but that won’t help you isolate devices that make slow yet lengthy energy draws.

You can make a pretty good guess using the Energy Vampire Calculator(Opens in a new window) from Duke Energy; put in a guess on how may PCs, chargers, TVs, monitors, printers, and so on you have plugged in full-time, and it’ll spit out a guess of how much you’re wasting. Even that charger block or smartphone is probably costing you something.

Vampires!
(Credit: Duke Energy)

To get specifics regarding your energy usage, you need an electricity usage monitor that tells you exactly how many kWh a device or appliance is drawing. It can be as simple as a “plug load” monitor that plugs into an outlet. You then plug the device/appliance into the monitor. Typically, an LED screen displays the consumption.

One of the simplest, least expensive, and best-known of the plug-load variety is the P3 Kill A Watt EZ, available at Amazon(Opens in a new window) and elsewhere. After a device pulls some power for a while, the monitor can auto-calculate how many kWh the device uses in a day, week, month, or year, providing an instant estimate. It also measures the quality of your line. The Kill a Watt EZ won’t work on all appliances, especially on items such as dryers or hot tubs, because it’s for use on 110- to 120-volt systems—not 220V and 230V, as you’ll find almost everywhere else on Earth(Opens in a new window).

(Credit: P3)

For those in smart homes, you can find a number of smart plugs with built-in energy monitoring. As for whole-house electricity-monitoring tools, there are several systems. They work via sensors placed on the lines (usually at the household junction box); the sensors talk wirelessly to meters and gather lots of data, usually uploading it to the web for you to access.

Some of these tools should be installed by an electrician, but a few are sold with the promise that anyone can install them. Brands include TED Pro, Sense Energy, and Eyedro. They usually sell for $299 to $349. Eyedro also offers cheaper home versions(Opens in a new window), as low as $99, depending on whether you want to support only Ethernet or Wi-Fi for monitoring or to add more sensors.  

What’s really cool is that a system such as the Sense Energy Monitor isn’t limited to just whole-house energy usage: It can also pinpoint the electronic signature of every device drawing power and uses algorithms to ID them and point you to the vampires.

What to Do With Vamp Energy Info

So, you’ve got a list of all the products in your house that are plugged in, from electric toothbrush charger to refrigerator, and you know exactly how many kWh each utilizes, and you’ve extrapolated that number into the cost per week, month, and year. What’s next? That’s up to you.

Some items you can’t unplug: say, the garage-door opener, the fridge, or the hot tub. Not even to save cash, unless you want to be stuck outside, let your milk get warm, or take a tepid tubbie with the hubbie.

(Credit: Shutterstock)

Bear in mind that some devices use the same power when in standby as they do when powered up, and they must be shut off for power-based peace of mind. A perfect example is that ancient fax machine your husband won’t get rid of. Or any old appliances, such as the answering machine on your old landline (just get Google Voice already). Your microwave oven isn’t drawing a lot of power by sitting there, but that clock on the front of the oven costs you even when you’re not cooking. The same goes for your coffee maker, toothbrush charger, and air conditioner: All those little LED lights on the front require current.

Smart plugs and power strips are the best way to take control. You can then put your smart home hub or smart speaker to work, helping you power off the insurgent vamps. (Over the holidays, this is a great way to make sure the Christmas tree and ancillary decorations don’t stay on all night, Clark Griswold.) And don’t forget the bulbs—using smart bulbs, or at the very least making a switch to LED bulbs, will make a big difference.

The more you know, the easier it is to save.