How to Calculate Your Electric Usage Costs per Individual Fixture or Appliance

Chugach Electric charges us on a monthly basis for the kilowatt-hour consumption (also known as kWh) displayed on the electric meter attached to our house.  If you look on your monthly bill, you’ll see “Total kWh Usage” in a box near the top of the page.  The number in that box is determined by subtracting the meter’s “Previous Read” from the “Current Read”.  A simple explanation of how our meters calculate kWH is:

A 60 watt light bulb consumes 60 watt-hours in one hour (that’s watts times hours).  60 watts x 24 hours = 1440 watt-hours per day, if the bulb is left on around the clock.  1440 watt-hours = 1.44 kilowatt-hours (kWh).  Chugach Electric charges us by our monthly kWh usage.  If that bulb were left on for an entire 30 day billing cycle, it would be 1.44kWh X 30 days = 43.2, rounded to 43kWh on the bill.   Looking at your monthly bill, it can be rather confusing when you look at the “Description of Charges”, but bottom line…..Chugach Electric currently charges Anchorage residential consumers just over 13¢ per kWh (plus a monthly $8.00 customer charge for billing and accounting).  If you’re a real number cruncher and want to be even more accurate, use 13.25¢/kWh.  Therefore, if on last month’s bill your “Total kWh Usage” was 496, your “Total New Electric Charges” will be very close to $73.72 (496 X $0.1325 = $65.72 + $8.00 Customer Charge = $73.72).  The kWh charge cost can change somewhat on a quarterly basis due to changes in  Chugach’s fuel costs etc., but 13.25¢ will give you a good ballpark usage cost estimate at today’s rates.  By the way, the 60 watt light bulb in the example above cost you $5.70 (1.44kWh X $0.1325 X 30 days) for being left on around the clock for the entire 30 day billing cycle.

Note: Very few people are using 60 watt bulbs in their houses anymore since incandescents have been replaced for the most part with compact fluorescent bulbs (CFL’s).  CFL’s have lifespans five times or more longer than incandescents and use approximately 75% less energy.  Most of us have replaced our former 60 watt incandescents with 13 watt CFL’s and are using 13, 15, 18 or 23 watt CFL’s throughout the house.  You can even get dimmable CFL’s these days for use on three way lamp switches.  By the way in the example above, if it was a 13 watt CFL bulb (6o watt incandescent equivalent) that was left turned on around the clock all month long, it only cost you $1.24 (13kWh X 24hr X 30 days ÷ 1000 X $0.1325) , a 78% cost reduction from the 60 watt incandescent.  If it was a two or three bulb CFL light fixture you left on, then you have to double or triple the energy cost calculation.  However, you’re still money ahead of that single 60 watt incandescent light fixture.

The neat thing about knowing how to do the above calculations is that you can determine the hourly/daily/monthly energy cost on just about any light fixture or 120 volt plug-in appliance in your house.  Just keep in mind, that if for example you want to calculate the energy cost of lights in a particular room or fixture, you must add the total wattage of all light bulbs involved.  Example: What’s the cost of keeping my home’s exterior lights on during the winter?  You have four light fixtures with two 23 watt CFL bulbs per fixture.  The hourly cost calculation is:  4 fixtures X 2 CFL bulbs X 23 watts ÷ 1000 (to get kWh) X $0.1325 = $0.02438/hr, or about 2.5¢ per hour.  The daily cost calculation is: If you leave the lights on 16 hours per night, it’s $0.02438 X 16 hours = $0.39008, or 39¢ a night.  The monthly cost calculation is: $0.039008 X 30 days  = $11.70 per month.

Outside of lighting, to determine the energy consumption costs of other devices or appliances, you can either read the label (if it has one) or get actual kWh numbers by borrowing a small usage meter from Chugach Electric for free.  Plug the meter into a wall outlet, then plug any 120v device into it  and get the kWh energy consumption readout.  Just call Chugach at 563-7365, or e-mail and request a “Kill-A-Watt EZ” meter.  In addition, on Chugach Electric’s website (you’ll have to log in) under the Energy Efficiency/Smart Power tabs, you’ll find a link to their do-it-yourself Home Energy Analysis calculator.  It involves some of your time filling in the blanks, but you’ll get an idea of the energy cost of various electrical items in your home.  By the way, I own a “Kill-A-Watt EZ” meter myself and if you live in the area and would like to borrow it, just click on the “About the Author” tab at the top of this page in the menu bar, get my contact information at the end of that article, and call me or e-mail.

Back to lighting again, there are also Halogen, LED, and standard Fluorescent bulbs and fixtures that are commonly available for residential use.  Halogen bulbs are hot, bright and use lots of energy.  500 watt Halogen residential outside motion-detection activated lighting fixtures can be replaced with LED fixtures which reduce energy consumption by 90%.  LED Bulbs have instant brightness when turned on vs. CFL’s which may take a minute to get to full brightness.  LED bulbs are very energy efficient and long lasting, but currently very expensive to purchase.  You can easily spend $20-$30 or more per bulb, depending on what you’re getting.  It is just a matter of time before prices come down and LED’s take the place of most CFL’s, but we’re still a few years away.  Standard fluorescents are the four to eight foot tubular fixtures that many of us have in our garages.  I converted my fluorescent fixtures from T12 to T8 bulbs by replacing the ballast and bulbs.  This resulted in instant, brighter, no buzz and more energy efficient lighting in the garage.  You can go online to get tips on how to do this, or ask me in the comment section below if you’re interested.  Enjoy calculating and minimizing your electric consumption, if so inclined.

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One Response to How to Calculate Your Electric Usage Costs per Individual Fixture or Appliance

  1. Anonymous says:

    Good article Pete!

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