What's the difference in setting the AC to 68F or 78F when it's 97F outside?

Question

This sounds like it would have an easy answer, but I'm not sure. I've thought and thought and thought about this. Some of us have grown up thinking that turning on the AC (air conditioner) is a bad thing. This of course, comes from the financial impact our electric bill will have on our wallet. My wife loves to run the AC. She also likes it around 68F. I pay the bill; what does she care? She's comfortable. While 68F seems just a bit chilly for me and the kids, we can always 'cover up'. It's also a constant battle. Every time I walk past the thermostat, I bump the temperature up a couple of degrees to 70F. When she passes by again, she notices the 70F and promptly turns it back down to 68F. (At least she's gotten out of the habit of setting it to 65F!!) It's 97F outside. Nice and cool inside. One day I was bumping the thermostat back up to 70F when I realized something... Within a few minutes, the inside temperature will rise to 70F and the AC unit will have to kick on again anyway!! Am I really saving any money with this game we play? Why not just leave it set to 68F and be done with it? As long as I don't allow the inside temperature rise above what the thermostat is set to (by leaving doors open), I don't see what difference it makes. The AC unit is running one way or another. I could see how turning the AC OFF while making a trip to the store could actually cost more than just allowing it to maintain a steady temperature while you were gone for a couple of hours. If you had turned it OFF, the inside temperature would be allowed to climb while you were out. When you return from the store, you'd have to turn the AC on. At this point, the AC would run constantly for a very long time to get the temperature back down to the desired comfort level. People tell me that they have their thermostats set to 78F or 80F at their houses. I can't imagine that. When I tell people that my house stays at 68F the first thing they mention is that they wouldn't want to have to pay my electric bill. When I tell them how much my bill is, they can't believe it. They're paying the same amount. Am I just talking non-sense here or is there something to this? This had perplexed me for quite some time now and I would really like to hear from somebody who knows. Thanks.

Answer 1

If your house is well-insulated, windows & doors stay closed,

& you don't have sun shining in the windows for part of the day,

a couple of degrees will not make much difference to the bill.

But your friends may not be telling the whole story to you.

Answer 2

Your electric bill depends on a lot of factors.....how well your house is insulated, how efficient your ac is and it can also depend on how often your ac starts and stops.  The difference between 68 and 70 degrees isn't all that much.  Maybe you two should just compromise on 69 degrees?  When I leave for work, I turn the ac down to 80 degrees and it usually doesn't get hot enough in my apartment until just before I get home.  You could get a programmable thermistat and set it so that it turns off during the day when no one is home and start up 30 minutes before you get back from work.  That way it will be cool when you walk in the door and it won't be unnecessarily running while your gone.  

Answer 3

If the system is sized right and in good working order at 75 she will cycle as designed.That's what I leave mine on.Yall are only tricking yourselves thinking going from 68 to 70 is doing anything besides just looking at the number.

It will run continuously no matter if she is on 68 or 70.

Don't you see?Normal comfort level is 74 or 75 and it will cycle at the stat as designed unless it is extremely hot outside.The a/c is not designed to keep a home 68 in the heat of summer.It will run and run and run.

Just be very careful about short cycling the compressor at the stat.Short cycling is the single most damaging thing you can do to the compressor as a home owner.

I have replaced hundreds of compressors that the cause of failure was customers,who just couldn't resist the urge to tamper with the stat every time they were near it and kept short cycling the compresor.

Answer 4

wow, i've never heard of a system being able to pull the temp down 29 deg. diff from outside air...u must have a h**l of a system!  the norm is 15-17 deg diff from outside temp to inside temp......

only savings for u would be that once the temp outside cools down at night, if u had it a 70+, the unit would cut off sooner......

lic. gen. contractor

Answer 5

this is not a a/c problem it is a marriage problem!

Answer 6

in setting your thermostat at 70 and leaving it your ac unit wont have to kick on on off all the time from changing the temp.  We have ours set a 78 degrees and our house is well insulated it keeps the temp comfortable without the outside unit having to kick on and off all the time.  The outside unit at our house runs about 20 minutes on avg during a one hour period at 100 degrees outside and believe me 78 feels very comfortable after being outside for awhile.  Dont keep bumping it back and forth all the time because all it does is keep cycling the outdoor unit which in the long run will be very costly as you are shortening the life of the unit.  Find a comfortable setting (preferrably above 72 to save you energy and keep the outside unit from icing up) and leave it there.

And I agree with dawg.  I have never heard of a system pulling the temp down that far.  d**n good system dont wear it out.