Saving Electricity home As seen in Newsweek, Forbes, NPR, the Christian Science Monitor, CNET, PC Magazine, InfoWorld, and everywhere else. About  
Rebates & Tax Credits
for U.S. consumers

Incentives for installing insulation and for buying energy-efficient appliances like refrigerators, washing machines, and air conditioners are often available from local and state governments and utilities. You can see what's available at DSIRE, Energy.gov, and Energy Star.

Related sites:

Home Power Magazine. All about renewable energy for the home.

No-Impact Man. Blog about a family striving to have no net impact. (i.e., What little they use, they offset.) Inspirational.

Off-Grid. News and resources about living without being connected to a utility company.

Mr. Electricity in the news:

"Michael Bluejay runs the outstanding Saving Electricity site that I've mentioned many times before." —J.D. Roth, Get Rich Slowly

Deep Green (book) by Jenny Nazak, 2018
Small Steps, Big Strides: Building Sustainability Habits at Home (book), Lucinda F. Brown, 2016
How much money you'll save with these common energy-saving strategies, Lifehacker, Sep. 28, 2015
Radio interview about saving electricity, Newstalk 1010 (Toronto), April 21, 2015
How much does your PC cost in electricity?, PC Mech, Nov 21, 2013
How Much Electricity Do Your Gadgets Really Use?, Forbes, Sep. 7, 2013
Can my bicycle power my toaster?, Grist, June 10, 2013
Six summer debt traps and how to avoid them, Main St, June 5, 2013
To convert to gas or electric?, Marketplace Radio (NPR), July 20, 2012
8 Simple Ways to Reduce Household Waste, Living Green Magazine, June 29, 2012
Why is my electric bill so high?, New York Daily News, Mar. 27, 2012
Fight the Power, CTV (Canada's largest private broadcaster), Mar. 23, 2012
How to Cut Your Electric Bill, Business Insider, Mar. 20, 2012
Tips to save energy when using your computer, WPLG Channel 10 (Miami, FL), Feb. 23, 2012
How long will it take an energy-efficient washer/dryer to pay for itself?, Christian Science Monitor, Oct. 29, 2011
10 Easy Ways to Lower Your Electric Bill, Forbes, August 23, 2011
18 ways to save on utility bills, AARP, July 9, 2011
How to Save $500 Worth of Energy This Summer, TIME magazine, June 28, 2011
Hot over the energy bill? Turn off the A/C, just chill, Chicago Tribune, June 24, 2011
Cool Site of the Day, Kim Komando (syndicated radio host), May 29, 2011
This calculator shows how much you spend washing clothes, Lifehacker, May 6, 2011
What you pay when you're away, WCPO Channel 9 (Cincinatti), May 5, 2011
Spotting energy gluttons in your home, Chicago Tribune (CA), Apr. 7, 2011
Walnut Creek author has tips for livng a thrifty life, Contra Costa Times (CA), Jan. 24, 2011
Do space heaters save money and energy?, Mother Jones, Jan. 10, 2011
Energy steps to take for a less pricey winter, Reuters, Nov. 10, 2010
Should you shut down your computer or put it to sleep?, Mother Jones, Nov. 1, 2010
Energy saving tips for fall, Chicago Tribune & Seattle Times Nov. 7, 2010
10 ways to save money on your utility bill, Yahoo! Finance, Oct. 2, 2010
Mr. Electricity Ranks Refrigerators & Electrical Wasters, Green Building Elements, Sep. 8, 2010
The case against long-distance relationships, Slate, Sep. 3, 2010
10 household items that are bleeding you dry, Times Daily (Florence, AL), July 27, 2010
Cold, hard cash, Kansas City Star, June 22, 10
Stretch your dollar, not your budget, Globe and Mail, May 18, 2010
Auto abstinence, onearth magazine, Winter 2010
2010 Frugal Living Guide, Bankrate.com
Energy-saving schemes yield €5.8m in savings, Times of Malta, Dec. 20, 09
Four ways to reduce your PC's carbon footprint, CNET, Dec 2, 09
The day I hit the brakes, onearth magazine, Fall 2009
How Much Do You Really Save By Air-Drying Your Clothes?, The Simple Dollar, 2010
Enjoy the mild weather, low electricity bills, Detroit Free Press, Jul 18, 09
The most energy-efficient way to heat a cup of water, Christian Science Monitor, Jun 16, 09
Ten ways to save energy, Times of Malta, Jan 3, 09
Measuring your green IT baseline, InfoWorld, Sep 4, 08
Bald Brothers Breakfast (MP3), ABC Adelaide, March 27, 2007
Net Interest, Newsweek, Feb 12, 07
The Power Hungry Digital Lifestyle, PC Magazine, Sep 4, 07
Net Interest, Newsweek, Feb 12, 07
Answers to all your electricity questions, Treehugger, Jul 11, 08 Going Green, Monsters and Critics, Jan 6, 2007
A hunt for energy hogs, Wall Street Journal Online, Dec 18, 06

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Is it better to run the AC all day or turn it off when going to work?

Last update:  July 2013


There are lots of crazy myths about energy use, and one of them is that somehow it takes less energy to run the air conditioner all day while you're at work, than it does to have it off all day and then turn it on when you get home.
  The theory is that the AC has to work "harder" when the house is hotter.

So let me give it to you straight:  Turning the AC off when you leave  definitely takes less energy.  Period.  In my own test, having the AC run all day used 317% as much energy as turning it on after work and cooling it down to the same temperature.  My test was a bit crude and I won't be surprised if the penalty for having your AC run all day is actually a bit less, but the point is, there's definitely a penalty for running the AC all day.  The reason is simple:  If an AC is constantly cooling your home, the cooler house is a heat magnet, which invites more heat into the house, which the AC then has to remove, over and over.

To see why this is so we need only remember something from high school physics:  heat goes to where it's not.  If you bake a potato and then set it on the table, what happens?  Eventually it cools down to room temperature.  That's because the room was cooler than the potato, and heat goes to where it's not, so the heat from the potato transfers to the room.  Once the potato gets down to room temperature, the heat transfer stops.

Next example:  Put an ice cube on the table.  What happens?  It melts, of course.  But why?  It melts because heat goes to where it's not.  The room is warmer than the ice cube, so the heat from the room goes into the ice cube, which absorbs the heat.  That's what melts it.  The ice cube is basically a heat magnet.

Okay, so now think about your house.  You leave for work, and you shut the AC off.  It's warmer outside than inside, so heat enters your home.  You come home, turn on the AC, and the AC removes all the extra heat, once.  Now let's try it the other way:  say when you leave for work you leave the AC on.  The AC constantly removes heat from your home, making it cooler, so you've just made your house a heat magnet, just like the ice cube.  The cooler it is in the house, the more heat wants to enter the house.  By constantly cooling the house, you're inviting more heat into the house, which the air conditioner has to remove, over and over.

Now, you might wonder, "So why does my house sometimes get warmer than it is outside?"  One reason is that the energy from the sun is hitting the house, especially the roof, which makes the attic super-hot, and that heat migrates into the house.  If heat goes to where it's not, then why doesn't the heat from the house go outside where it's cooler?  The answer is that it does, but you don't get heat equilibrium instantaneously.  When you put the ice cube on the table, it doesn't instantly turn to water, and when you take the potato out of the oven, you have to wait a bit before it cools to room temperature.

But that's neither here nor there about whether to turn the AC off when you leave home.  It definitely saves energy to turn the AC off while you're gone.

Here's the test I ran:  I picked two days in which the outside temperature was projected to be similar.  On 9/18/12 with an actual high temperature of 86°F, at 7:45am with a starting inside temp of 77.7°F I set a window-unit AC to cool to 78°F and put it on the Energy Saver mode, which means that the fan turns off when it's not cooling.  By 6:30pm it had used 0.92 kWh of electricity.  The next day, with a starting inside temp of 77.5°F a high of 87°F, I turned on the AC at 5:30pm, simulating turning it on when getting home from work.  By 6:30pm it had cooled the room down to 78°F, and used only 0.29kWh to do so.

You can do the same test yourself.  Here's how:
  1. Pick two days with similar projected temperatures and cloud cover.
  2. On Day A, turn your AC off when you go to work.
  3. When you get home, write down the number on your electric meter.
  4. Turn on the AC.  Don't turn any other big energy hog on, like laundry machines, electric oven, etc.
  5. When it gets down to the desired temperature and shuts off, go check the electric meter again and see how much energy it used.
  6. Also record the time that the AC shut off (e.g., 6:30pm).
  7. On Day B, set your AC to cool all day when you leave.  Make sure everything else in the house is turned off.
  8. Write down the numbers on your electric meter, then go to work.
  9. When you come home, don't turn on any big energy hogs.
  10. At the same time as Day A, check the electric meter to see how much energy you used.
If you run such a test yourself, please let me know the results.