Credit: Analogy by Slug Signorino

Which scenario uses less energy in domicile heating, and thus saves more money: (a) before going to bed, turning the thermostat downward from 68 degrees Fahrenheit to 60, then turning it up over again in the morning time, or (b) leaving it at 68 all night? (Assume the outside temperature rises to 45 in the day and drops to 25 at dark.) I always believed (a) would use less energy, only people tell me that (b) uses less, considering reheating the house to 68 in the morn uses more energy than keeping it at that temperature all nighttime. This doesn't make sense to me, but I defer to your wisdom. —Bill Morrison, Ladysmith, British Columbia

Ah, yeah—Ladysmith, B.C., justly famous every bit the birthplace of Pamela Anderson. Pam left long agone, of class, evidently repelled past her countrymen'southward inadequate understanding of efficient furnace operation.

Lowering your thermostat during times when y'all need oestrus less (e.g., when you're asleep or out of the firm) is called thermostat setback; the equivalent practice in summertime is thermostat setup. In theory, thermostat setback and setup volition almost always save energy, based on the post-obit elementary principle of heat transfer: the charge per unit of heat loss (or proceeds) is primarily a function of the difference in temperature between 2 objects, such equally your house and the surrounding air. In the wintertime, the colder your house is allowed to get, the slower it loses heat. Although your heater may run for a while during the recovery period when it's bringing the house support to temperature, you still employ less free energy than you would keeping the business firm at a constant temperature.

A lot of people, not only in Ladysmith, don't get this—in fact they're baffled past the entire field of study of thermostats. One researcher estimated in 1986 that every bit much every bit half the populace subscribes to what he called "valve theory," namely the belief that the thermostat functions similar a gas pedal: the college you set it, the hotter your furnace runs. In reality, most furnaces pump out oestrus at the same rate regardless of the setting; they simply cycle on and off as needed to keep the house at whatsoever temp the thermostat dictates.

Declining to grasp the subtleties of home heating tin can be expensive. At one time the U.S. Department of Free energy urged Americans to install programmable thermostats, which tin can be set to automatically turn the estrus down when it'due south non needed. These devices were thought to generate savings of 10 to 30 pct, and close to one-half of U.S. homes now have them. In 2006, though, the DOE stopped pushing the thermostats, which aren't cheap, after multiple studies showed the actual savings was zero—not because the inventors hadn't understood the laws of physics, only because consumers didn't use the things right. They couldn't effigy out how to programme the thermostats, didn't believe they'd work and so didn't carp, set the temperature higher during the day and thereby canceled out the savings from the setback at night, and then on.

Used correctly, withal, programmable thermostats indisputably piece of work, and and so does setting back the thermostat manually, provided yous do it systematically. My indefatigable assistant Una conducted a long-term research project in which she installed a programmable thermostat in her firm, aggressively dialed back the dark setting for winter, then tracked her energy employ for three years, using data from the National Oceanic and Atmospheric Administration to correct for outdoor temperature differences before and after installation. Upshot: she saved about 28 percent on her wintertime gas bill, enough to recover the thermostat's $120 cost in 3 months.

Granted, Una'due south situation was unusual:

• Her preferred winter thermostat setting had long been a toasty 76.

• She gear up the overnight temperature on the new thermostat all the fashion down to 50.

• Her house is older, with poor windows and Eisenhower-era insulation, and may fairly be described as an free energy sieve. (Since a well-insulated business firm loses less estrus to kickoff with, any savings due to setting back the thermostat are likely to be modest.)

What kind of savings are more than typical? Tough call due to wide variation in heating systems, climate, and energy costs. One dominion of thumb is that each degree Fahrenheit yous set the thermostat back over an eight-hour flow translates to a ane percent savings in heating costs. A study of two identical Canadian examination houses showed an eleven-degree setback overnight and during work hours generated a 13 percent savings in gas and a two percent savings in electricity. A U.South. study of 2,658 gas-heated homes using programmable thermostats found a half-dozen-percent energy-use reduction.

Notwithstanding, you ought to run across some savings. If not, various confounding factors could be in play, one of which may be that you're a knucklehead. —Cecil Adams

Is there something you lot demand to become straight? Take it up with Cecil at straightdope.com.