Should you heat and cool an empty house?

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By Terri Williams
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Adjust the thermostat when you're away.

Should you heat and cool an empty house?

The first day of Spring means warmer air is just around the corner.  It also potentially means higher electric bills as you reach for the thermostat to cool your house.

According to the U.S. Department of Energy, heating and cooling accounts for 48 percent of Americans’ total energy consumption, meaning associated costs comprise a significant portion of the average consumer’s energy bill.  Can those costs be lowered by turning off the heat or air when the house is empty?

Short-term

It’s certainly tempting leave the HVAC on when you’re leaving for work or another day-long excursion.  If you’re like most people, you prefer to come home to a cool house in the summer and a warm house in the winter.

But is it worth it to leave your unit running for 8 to 10 hours in your absence?  No, according to energy experts.

The DOE recommends adjusting your thermostat by 10 to 15 degrees when you’re leaving for several hours.  (Also, for maximum savings, your thermostat should be set to 78 degrees in the summer and 68 degrees in the winter when you’re at home.)

Rather than relying on your HVAC, there are other ways to keep your house as close to the desired temperature as possible during your absence. For example, completely-closed, reflective blinds on a sunny window can result in a 45 percent reduction in heat gain.

Similarly, closing your drapes during the day can also lower the daytime temperature in your home. The DOE notes that heat gains can be reduced by 33 percent with medium-colored drapes that have white, plastic backings. During the winter, you should open your blinds and drapes during the day to take advantage of the heat.

Window shades are another way to either reduce or increase heat. Dual shades that are white and reflective on one side and dark and heat absorbing on the other can be flipped around for use during the summer and winter months.

Long-term

When you’re away from the house for an extended period of time – for example, if you leave on a vacation or the property is a summer home or rental property that is vacant – there are additional factors that should be considered when deciding whether to heat or cool the unoccupied house.

“It is more economical to leave the heating and cooling system off in an unoccupied building,” said Darin Nutter, professor and department head of Mechanical Engineering and 21st Century Leadership Chair in Engineering at the University of Arkansas.

However, depending on where your house is located and the time of year, Nutter warns you may want to think twice before switching off your HVAC system.

“There is one real concern base on the building’s location and condition – moist air entering the building and the potential development of mold,” Nutter said.

Air conditioners help to combat the issue, which could arise in climates that are warm and moist, Nutter explained.  “In the summertime, running an air conditioner not only reduces the air temperature, but also removes moisture from the air – and both of these factors can help minimize the potential for mold growth,” he said.

However, according to the Lawrence Berkeley National Lab, an empty house is not likely to generate water from washing, cooking or other related activities, therefore the probability of moisture causing an issue is low.

On the opposite side of the weather spectrum, another concern is frozen plumbing in the winter. The DOE warns against letting the inside temperature of the house drop too far because the kitchen and bathroom pipes may not be insulated. A thermostat setting between 40 degrees and 45 degrees should provide a sufficient buffer.

The LBNL also notes that homeowners may be able to prevent pipes from freezing using other methods, such as properly draining water from the pipes and wrapping tape heaters to toilets, pipes and traps.

Terri Williams is a freelance journalist with bylines at The Economist, USA Today, Yahoo, the Houston Chronicle, and U.S. News & World Report. Connect with her on Twitter or LinkedIn.