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Bundle Up Your Overcoats!

Adding more layers of clothing helps us keep warm in the winter by reducing heat transfer. But Frosty seems to do just fine without any additional layers.

In much of the country, including NC and GA where I just spent a couple weeks, the weather is quite “seasonal,” meaning it is getting cold—right on schedule of course. As the Earth tips on its axis, the sun hangs lower in the sky and, in the northern hemisphere, shines for less time each day. The good news is that we have nearly reached the shortest day of the year—the Winter Solstice is on December 21st. More and more we notice the loss of summer’s stored heat.

In Vermont, the coldest weather is yet to come. Traditionally, the middle of winter, when you should have ½ your woodpile left, is January 28th.

Wherever I travel I notice that people are dressing more warmly. Again, no surprise! We tend to become “acclimatized” to our local temperatures, and when they dip into winter mode we break out our warmer clothes. Whether it is a light jacket, a sweater, long underwear or a heavy down parka, clothing helps us control heat transfer from our warm bodies to the cool air surrounding us.

All three modes of heat transfer are in effect. Any clothing we put on quickly changes the transfer by radiation and, to some extent, convection. Both can have a significant benefit but we need a good wind barrier to really minimize convective losses. However, there is little comparison between a lightweight windbreaker (which can achieve these reductions) and a heavy down jacket. The thicker and more effective the material (like down) the better you can control conductive loss—and that is what makes us really feel warm. The air pockets in our clothes are what does the hard work of reducing conduction—therefore, avoid very tight clothing if you want to stay warm. Dressing in layers of nearly any material works well to effectively trap warm air.

Most of us also understand how important it is to keep our heads as well as our hands and feet warm. When any of our extremities get cold, we really feel cold! Keeping the body core warm helps but it doesn’t do the job by itself.

Also, when our clothing gets wet, whether from an external source or our own perspiration, we can wind up in trouble fast. Even in temperatures that might not seem so cold, keep dry if you want to stay warm!

Wherever you live, enjoy this part of the year but take care to stay warm while you are out playing or working. I’d love to see some thermal images of how you keep warm!

Thinking Thermally,

John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner

3 comments to Bundle Up Your Overcoats!

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