A smart solution for a thermostat-war zone
By Jay MacDonald • Bankrate.com

The more coldblooded among us, those who actually prefer it warmer in summer and colder in winter, like to point out all the money our metabolism will save the household in heating and cooling bills.

And we have a point -- up to a point -- says Harvey Sachs, director of the buildings program for the American Council for an Energy-Efficient Economy.

The key lies in what Sachs calls "setbacks," those periods when you turn the thermostat down (in winter) or up (in summer) to conserve energy. Typically, there are three basic ones: sleep mode (midnight to 8 a.m.), work mode (8 a.m. to 4 p.m.) and home mode (4 p.m. to midnight).

"As a rule of thumb, you'll realize a 1- to 2-percent savings for every degree if you're doing eight-hour setbacks," he says. "It will be toward the higher end if you're doing two eight-hour setbacks and toward the lower end if you're doing one."

Let's look at it in practice. Say you normally set your thermostat in winter at 70 degrees Fahrenheit, and the heating/cooling portion of your energy bill works out to $100 per month. If you set back that temperature to 62 for the overnight and workday periods, you could cut your bill by $16 per month (2 percent of $100 = $2, times eight degrees = $16). A similar savings would apply in summer if you did two eight-hour setbacks from 70 to 78 degrees.

But Sachs says fighting over the thermostat for a couple hours of TV viewing in the evening -- winter or summer -- won't make much difference in your energy bill.

That's because it takes longer to heat or cool the contents of your home than it does the air. "If you just get into an evening's worth of thermostat wars, you're probably going to heat up the emotions more than the house," he says. "If you turn it up for a half-hour, you're mostly heating the air, which doesn't have much heat capacity."

In fact, if you do winter setbacks with a heat pump, as opposed to a furnace, your penny-pinching can actually cost you money.

"Say you drop the temperature overnight to 62 degrees, then set the thermostat to bring it up to 70 degrees in the morning. The normal thermostat can't do that without resistance heat, which involves turning on what amounts to a set of very heavy-duty toasters inside your air ducts. These things burn at 10 kilowatts or so, much more than an electric water heater, so they bring the temperature up very quickly but send your electric meter spinning like crazy," Sachs says.

The solution: Buy a smart heat-pump thermostat ($30-$150), which uses the heat pump itself to gradually adjust to preset temperatures without activating the resistance heaters.

But even the hottest couple can turn cold over the temperature setting of their love nest, see "Resolving a marital conflict: thermostat wars" for more.