When to Turn Your Heat Down

Programmable thermostat
Programmable thermostat

By Lori Bongiorno

Does turning your heat down when you go to sleep or leave the house for extended periods of time actually cost you money?

The answer is a resounding "no," according to experts at the Department of Energy (DOE), Lawrence Berkeley National Laboratory, Ecos Consulting, and the Natural Resources Defense Council.

However, there's still a common misconception that if you set the temperature of your thermostat back, then your furnace will have to work harder (and therefore cost you more money) to warm the space back up.

The truth is you aren't going to spend more in terms of energy or money by setting your thermostat back, says Ed Pollock, at the DOE. In fact, you'll always save money by setting back.

The real question is how much savings you'll get. The answer is very much dependent on several factors including where you live (how cold it gets outside), how efficient your furnace is (how long it takes to heat your house back up), and what kind of house you live in (how much insulation you have).

The amount of energy you put into a house to keep it warm partly depends on the temperature difference between inside and outside. The bigger the difference, the more energy you use. Setting your thermostat back cuts the temperature difference between the inside and the outside so you'll use less energy.

It does take more energy to bring the temperature back up, according to Jim Lutz, a researcher at Lawrence Berkeley National Labs. But, you'll still save money.

Let's say you turn your heat down for 8 hours and it takes an hour to bring your furnace back up to a comfortable temperature, you'll still get around 7 hours of savings, says Lutz. "I wouldn't turn it down for half an hour, but if it's for several hours I would," he says. At what point does it make sense for you to turn your heat down? There is no definitive answer, but Lutz says around 4 hours is a good rule of thumb. The longer the time period, the greater the savings.

How much money you save mostly depends on how long it takes your furnace to heat your home and how well insulated it is. If you live in a leaky house with an inefficient furnace, you'll save more by setting your thermostat back than if you live in a tightly sealed house with an efficient furnace. (One caveat: If you have an electric heat pump, then it may not make sense for you to turn your heat back at all, but Pollock recommends that you call in a professional to help you get systems in place to make it worthwhile.)

You can set the thermostat back manually or you can have a programmable thermostat do the work for you. If you decide to go with a programmable thermostat, it is essential that you program it. If you don't, then you will not save energy and money.

You won't see the Energy Star stamp of approval on programmable thermostats made after December 31, 2009, because many consumers don't actually program the thermostats. Energy Star can't guarantee energy savings unless consumers use the devices properly. Here are guidelines for choosing the right programmable thermostat to meet your needs.

The U.S. Department of Energy recommends setting your thermostat to 68 degrees while you're at home and awake. Here's the DOE's math on what you'll save: About 5 to 15 percent a year on your heating bill if you turn it back 10 to 15 degrees for at least 8 hours (as much as 1% for each degree).

Energy Star suggests maintaining your home at 70 degrees when you're awake and turning your thermostat down at least 8 degrees when you're asleep or out. Regardless of what temperature you decide on, the real key is turning the heat back when you can.

The bottom line: "It is absolutely better to turn your furnace down when you are away or asleep. There's no comparison to running it all day versus for a short while when you return," says Dave Weigel at Ecos Consulting.

Environmental journalist Lori Bongiorno shares green-living tips and product reviews with Yahoo! Green's users. Send Lori a question or suggestion for potential use in a future column. Her book, Green Greener Greenest: A Practical Guide to Making Eco-smart Choices a Part of Your Life is available on Yahoo! Shopping and Amazon.com.


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