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Myth Buster: Can a Thermostat Setback Save on AC Costs?

May 21, 2019

Summer – bringing warmer days, sunny skies and a potentially high electric bill. With rising temperatures outside it is always a relief to retreat into a cool, air-conditioned home. But as electricity usage spikes during the summer months and bills become more substantial, many look for ways to save. So, what can people do to save money on air conditioning?

When it comes to what will save the most money on air conditioning, there has been some conflicting ideas. Some subscribe to the idea that a thermostat setback during the weekday will save more money by not cooling an empty house. Others believe that it takes less energy to maintain the temperature throughout the day, ultimately taking more energy for the AC to cool the house to the desired temperature after implementing a setback all day.

To discover the best way to save money on energy this summer, the Data Science team analyzed these two hypotheses to find out which delivers the most savings.

The Analysis

Many households are unoccupied during the weekday, with people at work and the kids at school. The team compared energy usage of homes that did not set back their thermostats, to those that used a setback between 1° to 10° over an 8-hour period, while controlling for outdoor temperature.

Because the outdoor temperature and the desired internal temperature are principal factors of this analysis, let’s assume for the interpretation of our results that the average outdoor temperature is 85° and the desired internal temperature is a refreshing 68°.

The Results

When comparing the amount of energy required to maintain the temperature of a home at 68° to the amount of energy needed to cool the house after the setback, there was a significant reduction in energy usage for homes that used a setback.
The analysis showed that houses that increased the temperature of their home 1° compared to those that didn’t, used 2.4% less electricity on cooling. Those who had a setback of 2° over an 8-hour period saved 4.5% on energy. The saving continued to rise with each added degree setback, all the way up to a 10° setback which saved a nice 16.6% on energy.


So why does a thermostat setback use less energy?

Whether the setback is 1°or 10°, the air conditioner will run for less time during the setback period and therefore requires less energy to maintain the higher setpoint. Even with the energy it takes to cool the house back down, the air conditioning requires less electricity over that 8-hour period.

But more importantly – how does that energy savings translate into people’s weekly electricity costs? The graph below demonstrates the average savings across households.

During the workweek, people can save between $0.57 and $4.02 with an air conditioning setback. This is calculated based on the average cost of kWh across the United States, which as of 2019 was $0.12.

Now the real question – what does that save you overall during the summer months? If we assume that most homes run their air conditioning from June to the end of September, then that would save between $16.43 to $68.34.

Actual energy savings will vary based on the physical characteristics of the home, like the size, insulation and HVAC efficiency, and also on local weather conditions.  But the data indicate that regardless of these factors, homes can expect to save money and reduce energy consumption by using a setback on their AC while they are away.

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