AC temp up when out?
 

Hello, I have been turning my AC up 2º when we leave the house for a little bit. Our thermostat will automatically lower the temperature back to the original setting after 2 hours. If we are going away for more than 4 hours, I will bump up the temperature and put the ac on hold.
A friend has said I am using more electricity by bumping up the temperature because it will take more energy to bring the temperature back down. I just don't know if that is true or not. I have picked up this habit from our days up north when we would turn down the heat when we left.
Any thoughts or facts would be greatly appreciated.

I have no facts to back this up, but I’m with your friend. The AC works hard to bring the temperature back down. Plus I don’t like walking into a too-warm house. :)

I just heard this dicussed on a radio talk show last week. The person who was the subject matter expert said to leave the thermostat at a constant setting unless you are going to be gone for multiple days.

Your friend is wrong. The amount of electricity you use is determined by the total run time for the AC unit. So, increasing the temperature setting for a few hours will reduce the run time and save money on electricity. You may want to consider buying a smart thermometer, like Nest, which is supposed to monitor your activities and automatically adjust the temperture settings to save electricity. I just leave my thermostat at the same setting all the time.

Even if your second sentence is true, that doesn’t automatically make the friend wrong.

I have read articles on energy conservation that it is cheaper to leave the thermostat at the same temperature all the time.

When we lived in NJ our power company offered free audits and suggested ways to reduce your bill. Number 1 was set it and forget it. We leave the AC at 74 24 by 7.

Here is a quote from the Department of Energy (energy.gov) about saving electricity.

"In the summer, you can follow the same strategy with central air conditioning by keeping your house warmer than normal when you are away, and setting the thermostat to 78°F (26°C) only when you are at home and need cooling."

Your AC unit will basically use a constant amount of electricity when it is running. It cycles on and off to maintain the thermostat setting. So, if you increase the thermostat setting when you leave the house, the unit will not cycle on and off as much and you will reduce the run time. Yes, when you return and reduce the temperature setting, it will take a few minutes to bring the temperature back down, but the overall effect will be to reduce run time and electricity usage.

I agree, homes here are relatively leaky, including heat ducts in the attic, so you spend energy cooling outside air intrusion.

New homes use the Ecobee, you can add sensors that detect when you are away (same with Nest) and raise the temperature automatically when gone a couple of hours. You can use an app to adjust the temperature down before returning home.

Other thermostats use the GPS in your phone to automatically set and reset temperature when away.

Added advantage cooling from a higher temperatures is a longer cycle will remove more humidity.

Ah, another case where the experts don't agree! :icon_wink:

Just anecdotally, I used to fiddle with my thermostat, turning it down when I left the house and at night. I stopped doing that last spring and my electric bills have stayed pretty much the same.

Depends on how low you set it. Anything below 72 going to burn electricity. I know this cause my neighbor sets his at 69 and the A/C Is constantly on. Where mine set at 77 and runs 1/2 or more His his does. I can’t set mine below 74 due to my lungs congest.

Most of the AC units in The Villages are single stage units. They are either on or off, and when they are on, they are using a fixed amount of electricity per minute. When they are off, they use no electricity. The lower you set the temperature, the longer the unit will run, and the more electricity you will use. It is as simple as that.

73 OR 74 Degrees year-round. On a budget plan with Duke. It went down again last year to $147 a month.

Comfort #1 priority. There is no big difference with adjusting constantly.

When we go away for more than a day we put it on 80 Degrees.

How much can you save? Can't imagine it's significant since cost of the electricity here is cheap.

You are correct that the saving is not significant. I keep my thermostat set at 77 degrees all year round. My electric bill averages about 85 dollars per month. Although, a smart thermostat like Nest would save you a few dollars.

Well as the only commenter that has a whole house energy monitor for years with trillions of sampling points of electricity and not random speclation let me say this.

On average 1.6 to 1.8% of your total electricity bill is save for each degree higher the ac is set.

Is that a lot? In the world of electricity consumption it is. There is no magic solution to save ten or twenty percent, it all comes from small changes.

Try this device to find out for yourself, with most users saving 6-9% or so. That is everyday, year upon year.
Sense: Track energy use in real time to make your home more energy efficient.

Marathon Mans answer makes perfect sense. If you think about it. Initially you will save that electricity while the house climbs from at home temperature to away temperature. Once it reaches away temperature it will cycle on and off about the same amount of times to keep at that temperature. When you return it to at home temperature you will use most of the electricity you saved going up. That cycling on and off at the increased temperature setting might save, depending on how long you are away. If it gives you peace of mind and makes you feel good, DO it.

My sons have had terrific results with Nest thermostats. They “learn” your active-inactive times and set the temperature accordingly. They have many other capabilities as well. They’re more expensive obviously, but both sons say they are one of the best investments they’ve ever made.

I would just point out that, when you raise the temperature setting, the unit will cycle on and off, but it will not run as long and it will use less electricity to maintain the higher temperature. So, the longer you are away from the house, the more electricity you will save.

listen to your friend. why do you raise the temp when you leave?

I keep my house at 74° day and night in the summer and 70° in the winter. I don’t open the windows. That keeps the humidity low in the house. If I’ve been outside and I’m emitting humidity, I just turn on a ceiling fan. They help a lot. I used to turn down the thermostat to 60° in my Pennsylvania house in winter when I was gone for the weekend. But when I returned, it took about four hours to bring the house back to 70°, due to all the cold wood and drywall that had to be heated. Probably I didn’t save much. I didn’t notice the bill dropping. You can save a lot more by keeping your house several degrees warmer all the time in the summer or several degrees cooler in the winter. I know my limits. My dad prefers 76°, but that’s just too hot for me. Under 70° in the winter and I’m too cold. We vary!

I have Nest but I don't use the nest sense features. I raise the ac temp on the thermostat when I'm away and lower it from my phone when I'm on my way home. Nest allows you to monitor how many hours your AC runs each day. I've found that when I leave the temp constant, I use AC about 8 hours a day. When I'm away for several hours and I raise the AC temp and set it remotely prior to my return, the AC only runs 5 to 6 hours a day and the house is cool upon my return.

Temps
 

Please keep in mind We had mold treatment and were told NEVER have your house higher than 75 degrees

A/C bump up
 

My hubby (A/C guy 40 years) said not true with the latest thermostat & technology. It makes no sense to have it set low when your gone. We always set ours up 2 to 3 deg when we are gone because of possibility of mold, it might get too humid

I'm sure many here won't believe this but My thermostat stays @82 degrees. Perfect temp for me.

I’m certainly no expert on the subject but based on the documents we received when we purchased our house it’s best to keep the temp steady. Like you I’m used to adjusting the temp so this is a new practice for me.

We keep ours at 78, humidity stays at 56 which I understand is a good number

I lowered the humidity setting from 60 to 56% and raised the temp setting 1 degree. I don't know if it will matter on the bill but the comfort seems about the same. Just mentioning because no one mentioned humidity in the string.

Want to know for sure? Keep doing what your doing for a month or a billing cycle, then leave it at a set temp for the next month/cycle.

On a different note, we monitor different areas of our house with thermometers and it is never a constant temp everywhere in the house. Our termostat (next to the Master BR) is set to 77 all the time. The temp in our main living area where we spend most of our time is then 75, and at the far end of the house it is 73. The Master BR is 75 or 76. So nowhere is it actually 77. No, I have no real point, just an observation.

TIME, I think, is the key. If you're out for a couple of hours, raising (or lowering in the winter,) doesn't save any electricity. If you're gone for a day or more it makes more sense. I do like the "argument" that running the AC longer, to catch-up after returning from the higher setting, would reduce humidity better.

I DO LOVE THAT "EXPERTS" DISAGREE!

If you have a heat pump, leave the setting constant unless you are gone for a substantial period of time. If you have a regular air conditioner, bump it up 2 degrees while you are away for 2 or more hours. In TV our homes are well insulated. The AC will likely not run at all for quite a while. Bump it down when you get home if it is not comfortable. It may run longer, but this will also dehumidify the house while you are there. You get more comfort for your air conditioning dollar, and you might save $20 a month.

Interesting topic. When we are away for long periods of time we set the A/C at 81 and forget about it. When we are home we turn the A/C down to 73 before getting ready to go to bed and it stays there until we get up in the morning. When we get up we turn it up to 78. I have no proof to back this up, but I gotta believe that keeping the house at 78 during the hot sunny daylight hours saves money rather than keeping the house at 73 all the time? When we come into the house from being outside, 78 seems nice and cool to us.

You said...."When they are off, they use no electricity. The lower you set the temperature, the longer the unit will run, and the more electricity you will use. It is as simple as that. "

Maybe not.......There is a third condition you are ignoring.. An AC can draw 3 times as much current when it is starting then when it is running. So continuously starting and stopping your compressor will result in using significantly more power. Frequetly changing the inside temperature setting will cause the AC to start the compressor and cooling fan many more times then when you leave the AC set at one temperature.

If you are using a heat pump, it is even more important not to keep changing the control temperature. A heat pump is slow to recuperate. That is, it has to run a relatively long time to bring the inside temperature to the set temperature. In addition, the back-up aux. heater is frequently a resistive type heater, that uses a lot of electricity. Sort of like blowing air over a toaster. The aux. heater will typically come into play when the outside temperature is below 32 degrees and/or when the inside temperature is set to more then 3 degrees higher then the actual room temperature.

If you want to save money, replace your AC/heat pump with a unit that has a staged compressor. It will run as a low BTU unit when the outside temperature is mild and as a larger BTU unit when the outside temperature is extreme.

In our area of Florida, my staged heat pump runs as a 1.5 ton unit when the outside temperature is mild and as a 4 ton unit when the temperature is extreme. It typically runs as a 1.5 ton unit 84% of the time. Carrier recently introduced a heat pump that is infinetely varitable. That is, it will run on a wide variety of BTU levels to suit many different outside ambient temperatures. I've been living in Florida for 23 years. I have learned to leave my temperature controller set to 78 degrees in the summer and 72 degrees in the winter, except when I am away for more then 4 or 5 days. When I replaced my single stage heat pump with a two stage heat pump, I saved an average of $65.00 a month on my electric bill over the previous year when I was using a single stage heat pump.

You make some good points. Yes, the AC unit uses more power to start, but I don't think more startups would significantly increase your electricity usage because it only takes a few seconds to start the unit, and you pay for electricity by kilowatt hours. I believe that almost all of the AC units in The Villages are single stage units. That is because they are cheaper to buy, and the electricity is relatively cheap. You can save a little money by doing the things mentioned in this thread, but, for most people, it's probably not worth the effort.

Has anyone figured out the payback time to cover the cost of a Nest Thermostat? What does it cost?

It is not the temperature that causes a mold risk. It is the relative humidity going too high. When we were snowbirds, I had a humidistat installed so when we left for the summer months, we turned the humidistat to the recommended setting (if I recall correctly, it was 60% relative humidity) and set the thermostat to a higher temperature. If the relative humidity got too high, the air-conditioning went on until the relative humidity got down below the set level. The only problem we had was that some of our vitamins (D3 and Fish Oil) ended up sticking together. Other than that, no issues and saved a lot of energy cost.

That, unfortunately, is not sufficiently revealing (too many variables). The temperatures and humidity levels, to name two factors, will change in the subsequent month, as will other factors, e.g. oven cooking vs dining out, thus, raising the internal home temps, etc. I believe, to be useful, the test would need to be done under a more strictly controlled environment. Some of these "helpful" energy-saving devices come at a hefty price, as well (while we're on the discussion), necessitating a lengthy period to amortize the cost. Most folks are very familiar with what increases the cost of energy in the home; one of the biggest is hot water ---> raise the temp a bit and you'll save, likewise, for heating/cooling. What good does it do to spend $9.00, for example, on a sophisticated LED light fixture that illuminates an area that is being used for 30 mins total during a day/night. On the other hand, if the usage is such that the initial cost can be amortized in a short period = probably worthwhile. I don't believe it's any more complicated or requiring sophisticated monitoring devices than that, IMHO and, to be clear, I do love and appreciate technology but only for the convenience and value it supplies - not just for the sake of it.

Fred

Amazon has several types of Nest thermostats for about $200-$250. Apparently, you can even talk to some of them. I think the payback time would vary wildly, depending on your lifestyle. But, at least you'll have some one to talk to.

I love how the energy dept. says ok to raise the temp. when away and lower it to 78 when you want cooling. 78 is cooling???and comfortable! I don't care what you say after that statement. If when up"North" it is ok to lower the t'stat when your away because your heating system can recover much quicker than your cooling system mostly because the heating system has to work on what's called sensible heat while your cooling system has to work on both sensible heat as well as latent heat,which is basically water vapor or humidity. I always leave my t'stat set where I am comfortable unless I am away for several days and the raise it to about 80.
forty years designing, seling and servicing a/c systems in Miami.

Really??...what does raising the thermostat a whole 2 degrees save you on electricity..25 cents?

Some people just cant stop “saving” money.