Programmable Thermostats - Setback Misconceptions

[Admin]

You can save around 10% a year on your heating and cooling bills by simply turning your thermostat down. You can do this automatically without sacrificing comfort by installing an automatic setback or programmable thermostat.

A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies.  The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save.

View the Energy Star Website - Here

Electric resistance systems, such as electric baseboard heating, require thermostats capable of directly controlling 120-volt or 240-volt circuits. Only a few companies manufacture line-voltage programmable thermostats.

For steam heating and radiant floor heating systems, the problem is their slow response time: both types of systems may have a response time of several hours. This leads some people to suggest that setback is inappropriate for these systems. However, some manufacturers now offer thermostats that track the performance of your heating system to determine when to turn it on in order to achieve comfortable temperatures at your programmed time.

A Note for Heat Pump Owners

When a heat pump is in its heating mode, setting back a conventional heat pump thermostat can cause the unit to operate inefficiently, thereby canceling out any savings achieved by lowering the temperature setting. Maintaining a moderate setting is the most cost-effective practice. Recently, however, some companies have begun selling specially designed setback thermostats for heat pumps, which make setting back the thermostat cost effective. In its cooling mode, the heat pump operates like an air conditioner; therefore, manually turning up the thermostat will save you money.  Recently, however, some companies have begun selling specially designed programmable thermostats for heat pumps, which make setting back the thermostat cost effective. These thermostats typically use special algorithms to minimize the use of backup electric resistance heat systems.

Sources:
http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12720?print

[Admin]

After doing my own testing I disagree with the above article.

A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings.

In 2013 I used a 4C setback.  The house is 21C when I'm home and 17C during the day when I'm working.

In 2014 I used a 2C setback.

I used 26% less gas in November 2014 than I did in November 2013, even though November 2014 was 2% colder than November 2013.

I found using a 2C setback versus a 4C setback much more efficient.