Turning down the heat certainly is an eco-plus, given that 30 percent to 50 percent of a home's energy use in winter is for warming it.

Every degree lower can save roughly 2 percent of the heating bill.

Energy efficiency experts recommend 68 degrees in the daytime, 60 at night, governed by a programmable thermostat, which is especially important. It will keep you from waking up at 2 a.m., realizing you've forgotten to turn the accursed thing down.

But if anyone still doubts global warming, I can say one place it's definitely happening: In our homes.

In 1993, according to the federal Energy Information Administration, 29 percent of U.S. households set their thermostats at 71 degrees or above in the daytime when someone was home.

By 2005 - the most recent data - those high setters had risen to 40 percent.

This could hardly be a worse time for people to be bingeing on heat.

How can humans stay comfortable? The human body has a core temperature of 98.6 degrees.

To explore the thermal comfort zone, researchers studied nearly naked people in bikinis and Speedo-style bathing suits, sitting quietly in a draft-free room for three hours at 50 percent relative humidity.

A few tweaks later - like factoring out insulating body hair - they found that most humans are "thermally comfortable" at 78.1 degrees, says Alan Hedge, a Cornell University ergonomics expert.

Except that generally, men have more muscle mass than women, and that creates more heat.

Women feel the cold

However, men fiddled with the thermostats more often.

Obviously, comfort is subjective.

In the mid-1970s, Princeton University's Robert Socolow studied household heating in 32 identical townhouses in Twin Rivers, just off Exit 8 of the New Jersey Turnpike.

Some homes used double the energy of others. Part of this was due to varying construction. But some was also due to thermostat settings.

Socolow now heads the Carbon Mitigation Intiative, a joint project of Princeton, BP and the Ford Motor Co. to find solutions to global warming. And he keeps his own thermostat at 64 during the day, the mid-50s at night.

In a summary of other research, E Source, a Colorado firm that advises utilities on energy efficiency, found a wide range of indoor temperatures across the world, from 57 degrees in Japan to 62 in Norway to a whopping 70 next door in Sweden.

Comfort levels have changed over time, too.

In the 1920s, about 90 percent of workers in a U.S. light industrial plant rated 70 to 72.5 degrees "too warm." Standards for household comfort were then about 64 degrees. By 1986, the standard had risen to 76.

In my home, we're experimenting with 65 in the morning and evening, 55 during the day and at night.

Sweaters certainly help. E Source says a good wool sweater is worth 3.6 degrees.

A true comfort

My money is on our wood-burning fireplace. We got an insert a few years ago that not only stops heat from escaping up the chimney, but also has a catalytic converter-like device that burns off more evil emissions.

Still, it feels awfully chilly sometimes. Just the other night at dinner, my husband noted, "I think our food's getting cold faster."

Down in our basement are two heating oil tanks that, combined, hold 550 gallons. We filled them this fall.

Call it a silly game, an arbitrary goal. Or just stubbornness. But I am not going to have them filled again this winter.