Q&A: Raising and Lowering the Thermostat Uses More or Less Energy?

July 29, 2008
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In response to my recent post about our renewed attempts to lower our electricy bill, I received a number of questions about the new approach I was going to try to save electricity. This involved raising the thermostat when I left the house, and lowering it when I returned. Many people had heard that if you make your home hotter (or cooler) than it needs to be, your cooling or heating system will have to work harder to get the temperature back to a comfortable place when you return–therefore using extra energy in the process. This means that whatever energy you may have saved by turning off the a/c or changing the thermostat setting, you’ve now used up in cooling off or heating up the home. In fact, here is an amalgamation of two of these questions:

Q: Is it true that you’ll save more energy if you leave your thermostat at a single point throughout the day/I’ve heard that if you raise or lower your thermostat by more than eight degrees, you’ll end up using more energy getting the temperature back to where it was.

A: From what I can tell, this raising/lowering the thermostat idea is right up there with all kinds of urban legends. (In fact, there’s a discussion on Snopes.com, the ultimate website for snooping out urban legends, on just this topic. And the folks there seem to be perpetuating the myth.)

Why am I calling it a myth? Because every reliable (i.e. government or respectable energy website) I could find said the exact opposite of what these folks asked in the question. These websites showed that if you fiddled around with your thermostat’s temperature, you would actually save money in the long run. (Check out this Energy Star website chart on programmable thermostats that shows you how you could change your thermostat throughout the day and save $180 a year in energy expenses.)

Another website I like is Mr. Electric (dude needs a haircut but his advice is spot on). He also explains why you want to raise and lower your thermostat to save money. Scroll down to the question that beginsI was reading about turning the air conditioning off during the day to save on costs” to see his take on this topic.

Steven Harris, CEO of Knowledge Publications, a company that sells books on alternative energy, had this to day on the topic: “[T]he 8 degree difference has NOTHING to do with how hard the AC works during the day. It does NOT work more to cool the home from 85F back down to 70F when you come home. It would work harder to keep it at 80F all day long and then when you got home it would work just as hard moving the house from 80F to 70F.”

Bottom line: I’ll be keeping my a/c off whenever possible and the windows open, and when it’s warm enough outside that windows open isn’t an option, I’ll for sure raise the thermostat and turn the a/c to auto or off when I leave for long periods of time. The less energy I can use–and therefore pay out to PECO–the happier I’ll be.

It will be interesting to see what our next energy bill looks like, now that we’ve got these two measures in place. In addition, because we’re taking short trips, here and there, in the next few weeks, that means that we can leave the a/c off for extended periods of time. That’s got to save money. I’ll let you know what happens when the next PECO bill shows up.

6 Responses to Q&A: Raising and Lowering the Thermostat Uses More or Less Energy?

  1. Leah Ingram on July 31, 2008 at 3:07 pm

    Lesa:

    I had a post last month that compared window units to central a/c. Did that not answer your question? If not, what specifically would you like me to research on window units? Their settings to save energy? Let me know.

    Leah

  2. a conscious life on July 31, 2008 at 2:00 pm

    Thanks for all of the information.

    Any thoughts on window units? Would your research say the same thing?

  3. rebmoti on July 30, 2008 at 3:02 pm

    We have a programmable thermostat which we set to 78 most of the time and then 83 when we’re likely to be out of the house. We also have ceiling fans in most of the rooms and if we feel warm we just turn on the one in the room we’re in. We figure it’s more efficient than cooling the whole house. The hard part is remembering to turn them off when we leave the room! Also, sometimes we’ll turn the whole thing off and open the windows, particularly on cool mornings, but there haven’t been too many of those lately!

  4. Di Hickman on July 29, 2008 at 10:48 pm

    I have a goal to keep reducing our electric bill each month. So far since this journey is going down, gradually, but its going down.
    I have the a/c set to 83 when I’m home seems to be my magic number. But I only put it on if I’m pottering around the house. If I am in one room I just use the fan in that room.

    I also wash laundry in cold water now, no difference in cleanliness of clothes and saves a ton of electricity/gas.
    Line drying since well forever, unless it’s raining which is hardly ever (we live in So Cal).

  5. Roxanne on July 29, 2008 at 7:33 pm

    I interviewed an energy dude once for a piece I wrote in Natural Home, and he told me that doing it by hand to match your daily in and out of the house saves more energy and money than a programmable thermostat. Those are for people who forget. If you’re willing to do the work, he said it will pay off. He also recommended turning down the water heater at night, then back up in the morning.

  6. Theresa in Mèrida on July 29, 2008 at 5:20 pm

    I live in an incredibly hot and humid climate so cooling is a big deal here. We don’t have ac but we do have 12 to 20 foot ceilings and 14 inch thick walls. We use ceiling fans and personal fans. You simply don’t have to cool areas you are not in. When we lived in Arizona we used the ac but kept it less than cool and also used fans. My friends here who have ac sometimes all use the de-humidifier and run fans.
    regards,
    Theresa

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