Electricity Myths Revealed (Updated)

By Brooke Drake, October 10, 2011, Energy Efficiency

There are a lot of websites that offer ways to save energy. As it turns out, some of the ways that some sites provide can actually by wrong. According to the michaelbluejay.com, the site exposes some of these electricity “myths”, which I thought were interesting enough to share:

  • Myth #1. Does it take more energy to turn on a light than to leave it on? No. There’s no power surge when you turn on a light. Turning the light off ALWAYS saves electricity, even if it’s for just a second.

From Bounce Energy: There is always some sort of power spike when turning on lights regardless if the bulb has a ballast, rectifier, etc. However, for most cases, the spike is so small and quick, it uses as much energy as keeping the light on for about 10 seconds thus cancelling out. In addition to surges, turning lights on and off can add wear and tear which can lessen any bulbs life span. As stated in a comment below, the U.S. Department of Energy recommends that if a light is turned off for 5 minutes or less it should be kept on due to potential and significant bulb degradation.

  • Myth #2. Does it take more energy to turn on a computer than to leave it on? No. There’s no meaningful power surge when you turn on a computer. Turning the computer off ALWAYS saves electricity. Of course, you can also use the power saver feature.

Bounce Energy: The power saver feature does reduce the energy used; however, it doesn’t reduce it to zero. It still takes energy, although minimal, to keep your computer on even in sleep mode. Although it doesn’t seem like a lot, the energy used for sleep mode will add up over time.

  • Myth #3. Does it take more energy to cool a house in which the A/C has been off all day, than to keep the A/C running at, say, 85 degrees during the day? No. Cooling a hot house down at the end of the day always takes less energy than leaving the A/C running all day, even if it’s running on a high setting.

From Bounce Energy: There’s no sense cooling or heating your home during the day when no one is there. Rather than turning it off completely, raise the temperature to 80 degrees or higher when you leave your home for the day and reduce to 75 when home. If you use a programmable thermostat, program it for 75 degrees one hour before you come home, which will make it more comfortable when you walk in. During the cooler months, lower temperatures to 64 degrees and you’ll not only use less energy but save some money too.   According to EnergySavers.gov, by adjusting your thermostat up/down (depending on the season) 10-15 degrees for 8 hours can result in saving 5-15% a year on your heating/cooling bill.

  • Myth #4. Does a 240V device use more electricity than the same device designed to run off 120V? No. The electric company charges you for watt-hours, not volts, and the wattage is the same. To figure volts you use the formula V x Amps = Watts. A device that uses twice as many volts will use half as many amps, so the wattage will be the same — and so will the cost.

From Bounce Energy: Yes and No. Initially, a 240 volt device does run at a higher wattage (which uses more energy) compared to the same device if it ran on a single 120 volt line for the same amount of time. However, depending on the device’s design or inefficiency, the 120 volt appliance will probably take longer to complete the same job thus potentially using more watts. And since energy companies do charge based on kilowatts used per hour, using a 120 volt line would cost you more too. So in fact, the cost would not be the same. The reason behind this is a 240 volt device is actually being powered by two separate 120 volt lines each powering a specific device within. Whereas a 120 volt appliance is only running off of one 120 volt line.

I’d like to thank all of you who commented on this blog. We enjoyed hearing from you and appreciate your comments and feedback.

Here’s a few related posts you might enjoy:

Protect Your Home from the Energy Scrooges!

10 Ways to Keep Your Texas Electricity Bill Low Through the Summer Months

Get Your Home Ready for Spring: Make Every Room Energy Efficient


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Comments (6)


  1. Bret Zeller says:

    This has one false item. # 1 is incorrect. It states that it is always better to turn off a light, but for full size fluorescents, this is false unless they have a new-style electronic ballast. Older ones use more because they do require a surge.

  2. Bret Zeller says:

    I should emphasize that my argument includes the wear and tear issue. Although the guy on that site argues that wear and tear is negligible, the U.S. Department of Energy states that 5 minutes should be the cutoff for flourescents, because of the significant bulb degredation that occurs. It is widely known that CFL’s that are frequently turned on and off lose significant hour life (and for those of us who run CFL’s 24/7, it is easy to see how much longer they last, frequently years, and comparable to those that are off half the day, so perhaps double the hours)

  3. Greg says:

    It does take longer (more electricity) to cool a hot home if the thermostat has been turned off until you come home if you live in a hot climate. If your home temperature is 90 degrees and you come home and turn on you air conditioning set to 77 degrees, it could take hours to get the humidity and heat built up in the furniture, carpeting and walls down to a comfortable temperature. Your a/c will not shut off and could ice up causing compressor damage. get an Energy Star thermostat and set it to no higher than 85 degrees during the day and set to 77 about 1 hour before you get home. i have been an air conditioning contractor for 40 years.

  4. Davej says:

    #1 as stated is not always correct as traditional (hot-cathode) fluorescent tube lamps have heaters which must be heated upon start-up. This energy overhead traditionally has been identified as equivalent to 15min of lamp operation and any off time less than 15minutes between lamp usage is an energy loser. This style of lamp is prevalent in office settings.

    CFL (Cold-cathode Fluorescent Lamps) don’t have this heating issue issue

  5. John says:

    Myth #4 is poorly worded. And it is overly simplified. So there are two problems with it.

    First problem, of poor wording, implies an appliance owner might be encouraged to misuse an appliance (“the same device”) by trying to operate it at an inappropriate voltage. Be careful. A given AC device will be designed to operate at one nominal voltage, say 120VAC. (Rarely there is a switch that allows for operating voltage choices.) NEVER power any appliance by an inappropriate voltage… you could be injured… not to mention that the device could be destroyed.

    Myth #4 might be reworded:
    Does a 1500 Watt device designed to operate at 240 VAC (such as a built in electric stove) cost less to operate than a 1500 Watt device designed to operate at 120 VAC? Simple answer: NO. You pay for watt-hours. The device rating establishes the operating wattage. You control the hours of operation.

    Second problem, of oversimplification. 240V, built-in appliances are usually better-built than 120V counter-top gadgets that are portable. To wit: Better built, more expensive ovens are better INSULATED, than cheap appliances. Better insulation translates into savings at your kilowatt-hour meter. So mere wattage ratings don’t tell the whole story.

  6. JG says:

    “To figure volts you use the formula V x Amps = Watts.”

    A.) It should read “To figure POWER you use the formula”
    B.) That is the power for DC circuitry, calculating power factors for AC power involves vector math.