Every day, it seems, acquaintances send me articles about how to live better or save energy, many of which neglect the most obvious answers. They often report inventions that could increase fuel efficiency by 10 percent, ignoring the 500 percent increase you get from packing more people in a car. Others praise the junk foods with 10 percent less fat, not the people who eat 100 percent less junk food. When it comes to keeping warm in winter, likewise, we often overlook the simple.
We use many times more energy keeping warm than our ancestors did, partly for the reasons I mentioned last time: our houses rarely use the natural energy around them, and they leak the energy many of us import from far away. Most modern homes are many times larger than traditional ones, giving us far more space to heat. Another reason, though, is that inside these houses, more and more of us are alone.
In 1900, only one percent of U.S. residents lived alone, and half lived in households of six or more people. By 2012, 27 percent of Americans lived by themselves, and other Western nations saw similar trends. When extended families gathered under one (small) roof, the entire building could be heated or insulated more easily, and of course when people gathered in the same room, their body heat warmed the air. More people living alone, and fewer people per house in general, means more vast spaces to heat separately. (1)
For another thing, most of us keep our homes very hot these days. One U.S. organization assumes a normal indoor winter temperature of anywhere from 20 to 27 degrees C (around 67 to 82 F), but the British keep their homes at 17.5 degrees C (62 F), and a few decades ago kept them at 12 degrees (53 F), according to the U.K.’s Building Research Establishment. I don’t have statistics for Ireland, but homes here often feel colder still, and one local woman keeps her windows open during the near-freezing winter. Victorian Britons often slept with open windows – and they lived during the sub-zero nights of the “Little Ice Age,” an era when the climate was much colder than today. (2) (3)
Many old techniques allowed people to remain warm while sleeping, by transferring heat from the fire to some thermal mass and letting it radiate slowly. They put closed pans of hot coals or sand under the bed, or put their bedding atop “bed wagons” that left space underneath for heat sources. Some people in Central or Eastern Europe built masonry stoves, whose winding chimney heated a giant thermal mass of brick or stone – and some had a space for bedding attached to the stove itself, so that the fire would warm the brick underneath the bed. Hot-water bottles accomplished the same purpose with less of a fire hazard, and we still use them in our house through the winter.
If such temperatures sound intolerable, keep in mind that most of us dress poorly for the cold these days, even though we can buy highly insulating and comfortable clothes unavailable to our ancestors. Look at the everyday garments of people two or three centuries ago, and you see that what look like costumes to us were appropriately heavy and insulating. The business suit handed down to us from European gentlemen was made for a cold climate and colder age, even though people continue to wear them in paradoxically air-conditioned offices in Arizona and Florida.
Clothes insulate the body the same way that batting insulates the home, by trapping poorly conducting air pockets between the hot and cold spaces. As Kris De Decker of Low-Tech Magazine pointed out, though, insulating the body means warming only a tiny layer of space between us and our clothes – which costs much less energy than insulating our now-giant living spaces. If we feel warm, however, it achieves the same result.
Since every degree of indoor heat translates to about nine or 10 percent more energy, a 20-degree change in temperature could bring heating expenses from exorbitant to almost nil. As one of our home builders said, “If you’re wearing a T-shirt in the winter, you’re spending too much money.” (4)
As house insulation can be expressed using measures like R-values, clothes insulation is measured in the lesser-known “clo” unit. A “clo,” developed by scientists in the 1940s, is defined as the amount of clothing needed to keep a couch potato feeling about 21 degrees C (70 F) indefinitely.
If that sounds too vague, you could use the physicist’s definition: a clo is about equal to 0.155 m2 K/W. Or, if you’re an architect, you could translate it to home insulation R-values by defining a clo as 0.88 R. You could also say that a clo is about an eighth of a centimeter in clothing layers, or that each clo generally equals three kilograms of clothing weight. In everyday terms, however, it’s a three-piece business suit.
Photo: Baby polar bear with enough "clo" to survive the Arctic.
Every one-degree (C) drop in temperature can be compensated by putting on about 0.18 clo worth of insulation, and organizations like ASHREA and ISO have compiled meticulous lists of clothing and their clo-values, so a T-shirt is 0.1 clo, a sweater (or jumper, if you are in Ireland or the U.K.) about 0.2 to 0.4 clo, and trousers 0.25 to 0.35 clo. As De Decker points out in his article, if someone in a T-shirt simply put on more appropriate clothes – long underwear, heavy shirt and jumper – they could reduce their heating costs by 50 to 70 percent. (5) (6) (7)
Finally, one last and often-overlooked factor in winter warmth: most of our ancestors worked hard. Chopping wood, keeping animals, pushing barrows – even the most everyday chores from childhood to old age required physical activity that we rarely get today. Physical activity might be the most important factor in keeping the body warm.
My friends back in Minnesota were living with minus-40 temperatures recently – Centigrade and Fahrenheit, for that’s where the two scales meet – and that might seem to require more insulation than clothing can provide. Indeed, according to De Decker, keeping a resting person warm at those temperatures requires 12 clo, the equivalent of 12 suits layered on top of one another. Walk around, though, and that figure drops to four clo, and when running to 1.25 clo!
If all of this sounds overly Spartan, keep in mind that most of our ancestors lived in harsh winters with no central heating, no electricity, no coal, oil or propane. Go far back enough, and they even survived an Ice Age, and most of the time they not only survived, but prospered. If you want proof that we can thrive during cold weather on far less energy than we use today, just look around you.
1 – “The First Measured Century,” book from PBS, p. 92.
2 – American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
Standard 55-2010, “Thermal Environmental Conditions for Human Occupancy,”
3 – “How warm is your home?” BBC News, 3 March 2011, http://www.bbc.co.uk/news/magazine-12606943
The “Little Ice Age” was the period from the 1600s to the 1800s, when winters became much more severe. It may have happened, strange as it sounds, because Europeans introduced diseases to the Americas; up to 95 percent of the population of two continents died off, their farms grew back into forests again, the trees sucked up trillions of tons of carbon dioxide from the atmosphere, the greenhouse effect was quickly reduced, and global temperatures plunged. That era, when Londoners held “frost fairs” on the solidly frozen Thames River, is the source of most of our Dickensian Christmas imagery, the reason we sing about wanting a white Christmas even though most of our climates don’t allow for it anymore.
4 – “Insulation: First the Body, Then the Home,” Low-Tech Magazine, 27 Feb. 2011.
5 – ASHRAE Research Project Report RP-411: A Comprehensive Data Base for Estimating Clothing Insulation, January 1985. http://rp.ashrae.biz/page/RP411.pdf
6 – Gagge, A.P., A.C. Burton, and H.C. Bazett. A practical system of units for the description of the heat exchange of man with his environment. Science, 94: 428-430, 1941.
7 – Handbook of Clothing: Bio-medical Effects of Military Clothing and Equipment Systems, 2nd edition. By Ralph Goldman and Bernhard Kampmann, 2007