Is It Cheaper To Keep The Heat Air Condition On Or Auto?

I wanna save as much electricity as I can. Which one is cheaper, on or auto? 10 points to the best answer, thanks!

  1. Comment by D2
    February 9, 2010 @ 3:26 pm

    more power is used on start up,and people don’t understand that if you will set the thermostat to one setting and leave it alone,their cost would drop considerably,also if you leave during the day or night don’t turn the heat or air off,turn it up or down what ever the case may be,it takes a lot less power to cool/heat your home up/down a few degrees rather than having to start from scratch and cool/heat 20 to 25 degrees,and even more so with a heat pump,so the answer to your question is yes it is cheaper to leave the thermostat on auto

  2. Comment by Nick
    February 9, 2010 @ 3:55 pm

    My electric company sends me bills with bar graphs displaying my electric use. During hot months when the a/c is on alot, the bill is much higher. I am charged just as much for using the heater in the winter time.
    After experimenting with my thermostat, I found that keeping the a/c set to auto, at room temperature (75 degrees or so), keeps my electric bill as low as possible.
    There is no need to change the temperature if it remains 75. If I get warm I can turn a fan on for a minute and I will cool down quickly.
    Keeping the a/c “on” is very costly. That means even if the a/c is not blowing cold air, the fans are still on — which uses electricity.
    Keep your thermostat on “auto” at the highest temperature you are comfortable with to save the most money.

  3. Comment by kg7or
    February 9, 2010 @ 4:34 pm

    The general wisdom is that it takes less energy to keep a home moderately warm all day while you’re at work than it does to turn off the furnace, then turn it on when you return home. The furnace can run for hours to bring your entire house up to 68 deg. F from 55, for example.
    The best solution is a programmable thermostat that you can set at different temps for different periods of the day. Failing that, just turn it down a bit, instead of off, when you leave.
    Followup: on simple thermostats, “auto” sets your fan to run when the system starts your furnace or your a/c. “On” is a manual function that turns your fan on when nothing else is running. It’s useful for airing out the house, but not a lot else. Leave it on “auto” unless you want to manually run the fan.

  4. Comment by DAN THE AC MAN
    February 9, 2010 @ 9:36 pm

    i assume your question relates to the fan switch on the tstat… “auto” means the indoor blower fan will turn on and off with the heat and ac. “on ” means the fan will run continuously while the heat or ac will still cycle on and off by the temp setting….most people keep fan switch set to “auto” year round…thats probably the cheaper way to go.. the only reason to keep the fan switch set to “on” is to keep the rooms or levels of a home a more even temperature…this is normally only done in the summer when certain rooms or floors dont get cool enough compared to the room or floor where the tstat is located.. also some people like keeping the air in home circulating all the time during hot spells [ not all summer ]..air moving makes you feel cooler than when air is still such as when ac cycles off for a while…extra energy usage could be negligable if keeping fan “on” keeps you from turning tstat temp lower [ thereby running entire system ] just to get certain rooms or floors comfortable……dan

  5. Comment by Mick M
    February 10, 2010 @ 4:22 am

    If your thermostat switches from heat to air conditioning automatically, then set a temp and forget it. Even these may have separate fan control.
    If you mean a thermostat with separate heat and cool switching,
    then the auto setting is just for the blower only and I leave mine on
    auto to go on and off when the heat or ac is activated.

  6. Comment by ?Love?
    February 10, 2010 @ 4:24 am

    I do auto and keep it at 73 usually and really only turn it on at night. I have a low gas bill compared to other people. Also I live in south GA so we only need the heat at night.

  7. Comment by Recycling Education
    February 10, 2010 @ 5:31 am

    Choes “On” but set the temp. to a certain temp for energy efficiancy.

  8. Comment by sha-sha
    February 10, 2010 @ 7:56 am

    yes at least thats what I’ve been told

  9. Comment by zachary
    February 11, 2011 @ 5:18 am

    Recycling education shouldn’t be teaching anybody anything since they can’t spell choose or efficiency. just saying. Keep it on auto.

  10. Comment by Stephen, P.E.
    June 21, 2011 @ 8:53 pm

    Sorry, but most of you are wrong, as is the “prevailing wisdom” of the HVAC installers. I would suggest searching the web for a technical explanation by an engineer or physicist, not a pipe solderer. I’m a Professional Electrical Engineer with some HVAC experience and a very healthy background in both physics and thermodynamics.

    The total heat gain of a house determines the cost of running the A/C. The total heat gain is also proportional to two things – the difference in the temperature of the outside vs. the inside, and the amount of time this temperature difference exists. This is 95% of the “equation”. The other so called “variables” do not affect the final result: turning the A/C completely off during the day when not home uses less electricity than leaving it on, even at an elevated temperature setting.

    This is basic physics. If you integrate (sorry for the calculus) the product of the difference in temperature and time over a 24 hour day you will find that the the integral (which is proportional to the electrical energy used) is larger for an A/C that’s left on than one that’s turned off during the day.

    You can also think of it like this and avoid the calculus:

    Heat goes to where it’s not. The closer the temperature inside the house is to the outside, the less heat flows – if the temperature is the same there is zero heat flow. That’s why heat from outside goes into your cooler home. With the AC off, the inside of your house will quickly become hot and won’t absorb much heat from outside after that. When you come home and turn the AC on, or when a programmable thermostat turns it on before you get home, the AC removes all that heat. It may take some time, but less total time than it would take if you added up the total running time of the A/C if it were left on all day.

    But if the AC is on when you’re gone, then you’ve turned your house into a “heat magnet”. ***By keeping it artificially cool, it will absorb more heat than if it were hot***, and it will absorb heat at a high rate all day long. As the house heats up, your AC kicks in and removes some of that heat, but then the house is cooler so it sucks in more heat from outside, so your AC kicks in again and removes that heat, and so on and so on all day long. This is all wasted energy.

    This means that throughout the day, your house has absorbed way more heat than it would have with the A/C off, and you’re A/C had to remove it all. By contrast, with the AC off all day, all it has to remove is the heat in the house when you come home and turn it on.

    The actual numbers will vary, but there is zero question that running the AC all the time uses more energy than turning it on when you get home. This is not a gray area, it’s simple physics, and no person with any knowledge of this subject disputes it. Running the AC when you’re not home wastes energy, period.

    Now if you want to argue that it will shorten the life of the A/C compressor that’s a totally different subject. I’m talking strictly about electric energy usage to maintain a set temperature from evening until morning when most people are home.

  11. Comment by Henry
    July 20, 2011 @ 4:54 pm

    Glorious site with very informative information. It’s good to see that somebody on the internet in our industry is taking the time to offer this type of service. You are to be commended.

RSS feed for comments on this post. TrackBack URL

Leave a comment