Do Programmable Thermostats Save Energy?

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Thermostat setbacks aren't the same as programmable thermostats.

I see people misrepresenting programmable thermostat concepts all the time, so let's set the record straight here and now. Yes, when you set the thermostat back so your air conditioner or heating system doesn't run as much, you can save energy. I do it all the time.

It's simple physics . The rate of heat gain in summer and heat loss in winter depends on the temperature difference between inside and outside. When you get those two temperatures closer together, your HVAC system doesn't have to run as much.

I have a programmable thermostat. That's it in the photo above. Four years ago, before I replaced our air conditioner, we had a non-programmable thermostat. We actually saved more energy with the old one than we do now.

Wait a minute! I thought you said your programmable thermostat saved you energy?

No, that's not what I said at all.

What?!

That's right. I said I save energy by setting my thermostat back. Before I installed the new  AC, those setbacks saved me more energy because the old system was 25 years old and very inefficient. The less it ran, the more we saved.

The problem here is that people confuse programmable thermostats with thermostat setbacks. Two entirely different animals!

Many people who have programmable thermostats leave them in the 'permanent hold' position, as we do because we don't have a regular enough schedule. A lot of people with either kind of thermostat use setbacks to save energy.

Thermostat setbacks are where the energy savings come from.

Programmable thermostats may or may not be programmed or manually adjusted for setbacks.

So, the answer to the title question is:

No, programmable thermostats do not save energy. Not without some help from you anyway.

 

Related Articles

If You Think Thermostat Setbacks Don't Save Energy, You're Wrong!

Don't Set Your Air Conditioner Thermostat Like This

The Mad Hatter, Isaac Newton, and That Old Thermostat

 

Footnote

I know some of you think the term 'simple physics' is an oxymoron, but that's probably just because you didn't have a good physics teacher. Physics, though, really is simple. If the fundamental ideas weren't so simple, we never would have made so much progress. Right? Here: On which days of the week does gravity pull you downward? Which direction does heat move? See? I told you it was simple!

Comments

steve
Jul 19 2013 - 3:00am

here here Doc! I get highly annoyed when I hear the ads from the competitive electric providers touting the 'magic thermostat' that will save them money..........and is free with a 2 year commitment or whatever. 
 
Shut it off and you save money, run it and you spend money. Simple usage-based billing model. Not so much physics there. 
 
Its big business in Texas right now with famous actors touting the wonderful magical mystery thermostat that delivers like a fresh blanket of R-30 and is FREE when you sign up. 
 
There was an article recently about the cancellation penalty/charges for those that get the free magic t-stats when they sign up for long contracts for energy.....they put in full or more recapture-of-cost penalties in the contract if you cancel. Not new (or even fraudulent really unless they claim to save you x % just by installing it) just the carrot offer with the hammer binding legal wording in the paperwork. 
 
Its the cell phone model made for competitive electric. 
 
thanks for dispelling the current myth of the modern day potion for quick and easy energy usage reduction.

Charles
Jul 19 2013 - 8:05am

I thought I would save money when I installed a programmable thermostat to our existing HVAC system. I diligently MATCHED ALL THE COLORED WIRES, but there were a few wires left over and I thought they must not be required. The next month we received a $600 heating bill!!! Turned out the "emergency heat" option was simply the default mode of heating. 
 
I used to build computers from scratch so I know I'm capable of following wiring instruction. It doesn't hurt to ask for assistance in switching out a thermostat. For a few bucks extra it could save you lots of money.

Mark B
Jul 19 2013 - 10:13am

Your thermostat, if it is like mine (it looks exactly the same), has a "learning" feature. For example in the winter if I want to take the chill off in the morning by raising the temp 5 degrees and I set it to start at 6am, it will attempt to meet that setting BY 6am requiring an actual start much earlier. When delta T between inside and outside is huge I find little to no savings by setting back at night. Very frustrating indeed. My expensive programmable is a waste as I am now the daily programmer. 
 
Personally I have a secret fascination with physics dating back to grade school thanks to Mr. Roberts, my 4th grade teacher.

Bob Seaton
Jul 19 2013 - 10:30am

Using a programmable tstat, there's a summer strategy for controlling humidity in a vacant home (in Florida, to control mold/mildew). I call it the "Danny Parker Method": Operate 3-5 a.m. at very low temperature setting, as described here http://www.fsec.ucf.edu/en/publications/html/fsec-cr-1487-04/ But if you try this, you'll first need to disable the adaptive recovery mode if it's an intelligent programmable thermostat.

David Eakin
Jul 19 2013 - 1:22pm

"When combined with a power plan that varies the rate baesed on time of day programmable thermostats can be VERY efffictive tools to reduce enegy costs." 
Bob - only if the residents' schedule coincides with the setback times. If not, watch how fast the residents change their thermostats. 
 
Allison - one thing about programmable thermostats we see regularly around here (predominant heating climate) is that the electric bills increase when using the setback schedules. This is often because the thermostat sets the new (higher) temperature instantly from the lower setting and does not increase the temperature setting gradually. If using a heat pump, the system sees that it cannot meet the new temperature demand by heat pump alone so engages the auxiliary resistance heat strips - which drives up the electric usage. What is really needed (in heating-dominated climates) is an adaptive-recovery thermostat that automatically raises the room temperature gradually so as not to engage the auxiliary heat coils.

Skye Dunning
Jul 19 2013 - 1:42pm

There are some new "smart" thermostats that can actually save money. The Nest has a feature where it will actually turn on early to keep you out of the heat strips based on the weather forcast it gets from the internet. Also the auto-away and self-scheduling features should result in savings. It's early days and I haven't seen any data yet but it's going to be interesting to see how this goes.

Ted Kidd
Jul 19 2013 - 2:25pm

Does "Setback" save energy?  
 
Turns out the answer to that may be as variable and fingerprints.  
 
Does "Setback" lead to larger equipment sales? Yes, yes it does. So, maybe if you look at the big picture, setback has a significant unrecognized equipment and energy cost.  
 
My buddy Cameron Taylor is finding, with his new two stage AC, that recovering from setback (comparing weekday and weekend use) may use more energy than the setback saves: 
 
"I suppose I should prime the pump a bit regarding what I see in the charts: 
 
The peak consumption days, especially notable in the 2012 data, likely coincide with electric dryer usage. After my wife saw that and a similar one in the 2013 data, we started hanging our clothes outdoors to dry. That is reflected by a lack of sharp peaks in the 2013 data from 13 June to month's end. 
I am, in a preliminary sense, seeing little difference between the eight hour setback Monday through Friday, where the temperature setpoint goes from 75 to 78 between 0800 to 1700, and a constant setpoint of 75 maintained on weekends. Also, last year, the thermostat would set back to 76 at 2300 and back to 75 at 0600. This year it stays at 75 all night long. I would tentatively conclude, due to a combination of the building shell improvements and the two stage capabilities of the a/c system, that there isn't much benefit or penalty from our setback scheme. 
The setback scheme did seem to indicate a modest difference in consumption last year prior to reflective roof and two stage HVAC. 
On a recent 90+ degree day in June I measured the outdoor condenser's amp draw while it ran in 1st stage. It's a three ton unit with the Copeland Ultratech unloading scroll. Combined amp draw between condenser fan and compressor was six amps. When I installed the Evergreen ECM blower motor on the furnace June 14, I measured its amp draw as under an amp on low speed. While I would love to have data loggers on the electric consumption of both indoor and outdoor components (would make it much easier to break out a/c consumption over base load), if the majority of the time the system pulls on average about 7 to 8 amps TOTAL to keep us comfortable even on days approaching 100 degrees, that's pretty amazing. 
When the a/c is pulling down the house temperature in the afternoon coming out of the 78 degree setback on hot days, it runs in 2nd stage until it reaches 75, and then shifts to 1st stage. After that it alternates between 1st and 2nd until after sunset, where it then stays in 1st and finally cycles off. On weekends, when the setback never occurs, the system will run steady on 100 degree afternoons but not shift into 2nd stage. On the charts, the difference between the weekend behavior and the weekday pattern differ little. 
The highest peak in 2012 was 47 kilowatts. Highest peak in 2013 was 35. Daily average dry bulbs for both days, respectively, was 85 and 88. A warmer day on average in 2013, with electric dryer usage, yet a lower peak consumption by 17 kilowatts. 
When outdoor dry bulb averages and peaks are higher, but dew point averages and peaks are lower, consumption drops. The amount of latent load makes a difference. 
A basic observation is that we used over 30% less kilowatts in the calendar month of June this year over last year. IOW we sucked 283.66 kW less from the grid this year over last." 
 
So, keep sizing for quick recovery. Then throw in lots of dehumidifiers to manage latent... 
 
Setback, by creating impediment to aggressive downsizing equipment, may be costing us all a LOT! 
 
 

Skye Dunning
Jul 19 2013 - 4:16pm

I love that!

Pj
Jul 19 2013 - 5:29pm

Hi Allison, 
You would not believe the amount of fraudulent savings claimed by utility programs based on their assumptions that everyone with a programmable T-Stat is setting it back 6 hrs night and day. Also, I was just (today) read a 96 item report on the problems encountered with the nest t-stat from the largest res HVAC company in the US, who by the way, is owed by an electric company. If you are interested let me know. Further, it looks like there are some new things developing on the ability to see HVAC issues from the T-Stat data signatures, check out, http://www.ecofactor.com/  
I hope you are well, 
Pj  

Bob
Jul 20 2013 - 10:51am

Tedkidd, looks like you have an oversized HVAC unit if it only operates in 1st stage all the way to 100degrees. Most 14SEER+ systems pull about 4amps per ton @ 95F outdoor temp, so 7-8amps for your system on low speed isn't unusual. A single stage 15SEER 2 ton would have done the job at the same cost to run and cost 1/2 the money to install. Pull the EER @ 95F of a 14+ SEER single stage and you current system. In most cases there is less than 1EER difference, however the installed price is typically twice as much.