Question

Does a programmable thermostat really save 20% on my utility bills?

Asked by Brenda Nabors
Brooklyn, NY

Answer

Steve Saunders

Answered by Steve Saunders

Irving, TX

TexEnergy Solutions, Inc

March 15, 2010

You are in 100% control of what the thermostat can do with regard to savings and how much or how little you benefit from an investment in a programmable thermostat. It is distinctly possible for a programmable thermostat to save you 20% on your utility bill. It is equally possible for it to save nothing.

If you think about it, you already have the “analog version” of the programmable stat. The analog version is your personal action toward an energy efficient home.

  • When you leave for the day, you adjust the thermostat before you leave.
  • When you return, you adjust the thermostat for more comfort.
  • Before going to bed, you adjust the thermostat, and you adjust it again when you awake.
  • The programmable thermostat just allows you to tell the thermostat what you want it to do and forget about the manual implementation.

Therefore, the savings are really effected by what thermostat settings you choose and what you are comparing the savings against.  The truth or hype of the programmable thermostat energy savings come from whoever is in control of the thermostat -- and that can change daily.

Significant energy savings are possible

It is important to point out that significant energy savings are possible! I am from the South, where it is really hot in the summer. So, summertime examples tend to work for me.

Let’s just take a typical hot summer in Dallas / Fort Worth where the temperature is near 100 degrees every day for the month of July. Your monthly bill has a base utility usage that is not particularly dependent on the outside temperature. That base billing amount is for lights, appliances, television usage, etc. … everything but the air conditioning system.

The AC unit runs a lot as the temperature outside increases. The AC system, if properly designed, will run almost constantly on hot summer days. It is designed to run without shutting off for hours and even days. 

Many people are surprised at the difference in cost based on the setting of the thermostat. The difference in power usage is about 10% for every degree of desired cooling.

Let’s try to put some scope on the relative difference in temperature and the energy savings. In a hypothetical example

  • Imagine that your utility bill for AC (not including base load) is $250 for a really hot month when you set your thermostat at 78 degrees for comfort and do not change it.
  • Then, the next really hot month, someone else in the home says I want to be cold in the home and sets the thermostat for 68 degrees.
  • The rough amount your utility bill would change is double.

So, in the 68 degree temperature month, given roughly the same outdoor weather – you would experience a utility bill for AC of about $500. These are pretty well-researched numbers -- approximately correct given similar inputs. And, there are lots of Texas homeowners with the AC portion of their utility bill running at $500 or more in the summer months.

Save 20% of the heating and air conditioning portion of your bill

The purpose of the example above is to show that there are big impacts on utility bill based on temperature setting and on usage rates. It seems like programmable thermostats fit the lifestyle of the average American family.

  • The adults work, the children go to school and the home is mostly empty during the day (except for pets). This is an ideal time to put your thermostat on a timer and to set the desired temperature higher while no human occupies the home.
  • They reset the temperature to a desired level when they return from work and school.
  • At night, when this same family is in bed and asleep, there may be no real difference to the sleeping family with regard to the temperature and it is another possible time to set the thermostat to call for less cooling and therefore less overall energy use.

For those who take the time to really think about their lifestyle patterns and usage … and program the thermostat to how they live, can easily save 20% of the heating and air conditioning portion of their annual utility bill. They might save more or less depending on the variety of factors that influence the run time of the HVAC system.

But it does not work for everyone

At our place, someone is home almost all the time and when they are not, the changes to their leave and stay patterns are not generally predictable. We have a programmable thermostat and do not utilize the programmable part.

  • Our family, like a great many others, turns the thermostat to “hold temp” and dial in a figure.
  • My wife is a person who likes to be warm. In the summer, that means thermostat setting of 78 to 80 degrees. To compensate, I have ceiling fans located wherever I sit or sleep. That air movement is what keeps me comfortable and it cost less to power a ceiling fan for one person than it does to run the AC for our home at a lower temperature.
  • I do not capture the benefits of lower utility bills from set back thermostats – but, I still win most neighborhood brag fests about who has the lowest utility bill. (No one thinks to ask about our heating bill! Shush … don’t tell them.)

Purchasing a programmable thermostat

If you are in the market for purchasing programmable thermostats, there is a wide range of product options at most any price point you want.

  • You can buy a programmable thermostat at your local hardware store for as little at $22 and as much as $225 depending on the features, display unit, quality of program, brand name, warranty, reliability, product durability and ease of program management.
  • My personal advice is to not pay less than $100. That is an arbitrary number. But, it basically says that I think the low cost stats do not deliver value and paying a bit more will be worth the price.
  • One feature that is essential (and comes with more expensive stats) is a smart recovery feature.

The smart recovery feature

The smart recovery feature is marketed under different names (adaptive recovery, program intellisense, etc…).  Smart recovery is what tells the thermostat to start running the AC unit in time to cool your home to the temperature you desire when you get back after a long and trying day.

  • If it is 95 degrees one day and you want your home to be 78 degrees when you return from the office, your system may start cooling at 3:30 PM.
  • But, the next day, it may be 105 degrees and the home may still be at 82 degrees if it starts to cool at 3:30.
  • Adaptive recovery captures the run time and the start time on a daily basis. So, as weather heats up, the system comes on earlier to ensure that the home is the temperature you desire when you return.

This is a little known and little understood feature that adds greatly to comfort. It is imperative to have this type of feature in a heating mode where there is a heat pump.

Professional installation

As an adjunct to the question, I would personally recommend professional installation.

There are many reasons for professional installation but the best is just to get it done right the first time. Have your HVAC contractor bring one for your spring inspection and install it then.

The installation costs are less (they are already doing maintenance) and it is smart to get the wiring right and the right stat for the number and type of wires in your wall. Installed right and programmed effectively, you will find that you are much more likely to reap the savings as promised by the manufacturer.

Tagged In: heating cooling

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