Study Questions Setback Thermostats

December 15, 2000

A study from the Energy Center of Wisconsin (ECW) indicates that programmable setback thermostats may not provide the energy savings they seem to promise, and in the wrong consumers’ hands, may actually result in slightly higher energy costs.

However, improvements in thermostats and variable-speed motor technology could still result in energy savings.

“Programmable Thermostats That Go Berserk? Taking a Social Perspective on Space Heating in Wisconsin,” by Monica J. Nevius and Scott Pigg, states that “The average self-reported winter thermostat setting does not vary substantially by type of thermostat used,” whether manual or programmable.

In short, the study found that Wisconsin homeowners who learn how to work the programming on their setback thermostats, would also set back temperatures with manual stats, and usually to the same degree difference. Homeowners with little or no interest in energy conservation will resort to the “hold” function on programmable stats, bringing it back to a steady temperature with no setback.

The technology does not seem to change consumer behaviors.

The Human Element

According to the report, “Savings estimates for installing a programmable thermostat in a residential dwelling typically assume that the household members learn how to program their thermostat, choose to practice temperature setbacks, and are not already manually setting back their thermostats.

“But are these assumptions justified,” the study asks, “and if not, is the installation of programmable thermostats, especially when funded in whole or part with public money, justified?”

The 15% savings estimated by the Alliance to Save Energy has already been disproved to some degree. In 1997, researchers Cross and Judd found that “Actual energy savings from programmable thermostats were less than estimated, due to attrition from the use of programmable thermostats by homeowners and the fact that customers frequently already practiced a manual setback.”

The Wisconsin study surveyed 299 households in 1998 and 1999. The respondents, all owners-occupiers of single-family homes, were selected to accurately represent the state’s housing stock, including low-income households and new construction units.

Table 1. Thermostat distribution and its use (from the ECW study "Programmable Thermostats That Go Berzerk?" Taking a Social Perspective on Spae heating in Wisconsin," 2000).

Two-Thirds Still Use Manual Thermostats

Approximately two-thirds of the respondents reported that they still use manual thermostats to control their heating systems (see Table 1). Therefore, in Wisconsin at least, programmable setback thermostats have about a one-third market share, and it appears to be rising at a rate of about 2.5% per year.

Respondents reported setting their thermostats at a mean average of 68°F (setpoints ranged from 59° to 74°). It’s worth noting that while owners of setback thermostats reported that they set back temperatures lower than owners of manual thermostats, during non-setback times, programmable ther-mostat owners raised the temperature setting higher, essentially negating their deeper setback.

According to the report, these findings imply that “The mere presence of a programmable thermostat in a home has a minimal effect on heating energy use on average.”

To further clarify homeowner attitudes about programmable thermostats and energy conservation, the ECW interviewed 30 individual cases. Among owners of manual thermostats, 14 cases “both had a manual thermostat and were not interested in switching to the programmable variety,” the study states. “Of the seven households with manual thermostats that set their thermostats back manually during the winter, six felt that there would be no point installing a programmable thermostat for their households, and several expressed disbelief in the annual savings.”

Moreover, these homeowners stated that “The payback or the increased convenience were not worth the cost,” that “Setting the thermostat would be a hassle,” and that “They had heard of a programmable thermostat that ‘went berserk’ and overheated a house.

“Of those households that already had programmable thermostats,” the report continues, “three were positive about it and felt it saved them money, while two were unhappy with it and had stopped using the thermostat’s programmable features.”

Equipment Efficiency

According to a larger ECW study, “Energy and Housing in Wisconsin,” of which the thermostat study is a part, 82% of the 299 homes studied have a forced-air furnace; half are high-efficiency models. The remaining 18% are hot water/steam (16%) and electric baseboard (2%). (Note: Standard-efficiency units are identified here as being about 80% efficient; high-efficiency condensing units are at least 90% efficient.)

Since about half of all Wisconsin homes with a forced-air furnace have a standard-efficiency unit, it could be assumed that there is an energy-saving opportunity in replacing these units. However, the report advises that “It is not generally worthwhile to replace a standard-efficiency furnace that has many years of life left on it in order to get some heating cost savings.”

On the other hand, of those units likely to be replaced in the near future, most will probably be replaced with high-efficiency models, which “make up the majority of the furnaces that are sold in the state each year. Other ECW tracking data show that, statewide, more than three-quarters of furnaces sold in 1999 were high-efficiency models.”

And this brings us back to the programmable setback thermostats, which have come a long way, technology-wise, since they first hit the market. “Older versions were just glorified timers,” said contractor John Ambrosino, Total Temp-erature Control, Wakefield, MA.

While details were not available on the types of thermostats compared in the study (other than whether they were manual or programmable), it may be reasonably assumed that most programmable thermostats were older models.

Newer programmable thermostats with features like adaptive recovery offer more energy savings, because they can make intelligent control decisions between first- and second-stage heating. “We can gain savings for the customer between first and second stage,” Ambrosino said.

“If there is proper recovery between the setpoint desired and the temperature, the system runs at a reasonable, even rate,” even when the customer has defaulted to the hold function, which overrides the setback programming.

His company uses programmable thermostats as “complementary to the system. We choose our stats for the clientele. Pick the right product for the job.”

Publication date: 12/18/2000