Extra Cost of Having Set Back in Winter Hvac

MYTH BUSTER

Myth Buster: Using a thermostat setback for energy savings

Myth 1

Your HVAC has to work harder to heat your home up after using a temperature setback compared to not adjusting the thermostat.

Myth 2

It costs more money to adjust your thermostat as opposed to maintaining a certain temperature.

July 24, 2018

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For those of us in cooler climates, we are always looking for ways to save money on our heating bill. But what does it really take to save money on your HVAC during the colder days? There have been a few ideas floating around that present conflicting views on the best way to reduce energy usage and heating costs. These have mainly been focused on whether using a setback on your thermostat ends up costing you more when heating the house back up.
Now, for many households, people are at work or school at least 8 hours a day during the week. Those 8 hours when the home is not occupied are prime for a temperature setback. But many decide not to use setbacks because they think it will end up costing them more.
To settle this discussion once and for all, we took a look at what the data tells us about the using a setback.

The Analysis

We compared energy usage of homes that did not set back their thermostat to those that set the thermostat back by 1° to 9° over an 8-hour period throughout the day.
We decided to look at HVAC runtime and usage for homes. Homes that used scheduled setbacks for their HVAC were compared to homes that did not use any setbacks while adjusting for local 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 32° and the desired internal temperature is a cozy 70°.

The Results

When comparing the amount of energy required to maintain the temperature of a home at 70°, as opposed to the amount of energy needed to heat a house backup after the setback, the results were clear.
The data showed that houses that reduced the temperature of their home 1° compared to those that didn't, saved 4.50% on energy. Those who had a setback of 2° over an 8-hour period saved 8.30% on energy. Houses with a 3° setback saved 10.90%. Homes with a 4° setback saved 12.90%. Individual who implemented a 5° setback saved 14.50%. Those with a 6° setback saved 15.80%. People who chose a 7° setback saved 16.90%. A house that has an 8° setback saved 17.90%. And homes with a 9° setback saved a whopping 18.80% on energy.
Why does a setback save you energy?
With a setback, your HVAC is on for less time and therefore requires less energy to maintain the lower setpoint. Even when considering the amount of energy needed to heat the home back up, it requires less energy over a single sustained period, compared to an HVAC running more often throughout the day to maintain a higher temperature without a setback.
So how do these savings translate to dollars?
Most furnaces are rated based on their British Thermal Unit (BTU) consumption. However, we get billed by the volume of natural gas we consume measured in centum cubic-feet (CCF). Let's assume we have an average furnace that consumes 100,000 BTU per hour. A 100,000 BTU furnace uses 0.96 CCF per hour. This table shows the average savings you could achieve during a workweek with each degree setback.
In the setback graph, you'll notice that as your setback increases, the growth in energy savings and dollars begins to level out. This doesn't mean that a higher setback isn't worth it. In fact, it means the opposite. While these average workweek savings might not seem like a lot, over a six-month period (October 31st to April 30) excluding weekends (approx. 124 days), that can equate to more significant average savings.
So now you know. Any temperature setback, no matter how small, will save you money in the long-run. And now, maybe you can put that money toward a better use . . . like going on a trip somewhere that isn't so cold during the winter.