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Illinois Country Living

Doug Rye, licensed architect and the popular host of the "Home Remedies" radio show

Energy Solutions

The Dreaded Delta T
Stop the heat robbing force of Delta T with insulation

Yes, it’s cold outside and yes, I am still wearing my shoes when I go out to get the morning paper. It’s definitely winter right now, but spring will be here before we know it.

If you read and implemented the information in the last two columns, your floors should be warmer and your walls should be more energy efficient, therefore making your whole house more comfortable.

Certain types of wall insulation perform better than others when it’s cold outside and, particularly, when the wind is blowing. When it’s 75 degrees outside, no one really worries about wall insulation. In fact, they may open the windows and go fishing. When it’s 25 degrees outside, and the wind is blowing, no one wants to go out outside, much less go fishing.

You are, no doubt, aware that the wind chill temperature can be considerably lower than the real temperature. Generally speaking, non-heated moving air is not conducive to comfort in the winter.

You may be asking, “What is Doug getting at?” Well, just bear with me; I’m getting there.

You’re probably aware of wind chill, but you may not be aware of another type of air movement, which we call a “driving force.” This phenomenon occurs when there is a temperature difference between two locations, such as the interior and exterior of a house. That temperature difference is called a Delta T.

In nature, warm air always moves toward cold air. Think of it this way — the hot air is trying to get out of the house in the winter, but in the summer, the hot air is trying to get in the house.

The greater the Delta T, the faster the air movement and the greater the driving force.

Here’s a good example. When you open an oven door, you can feel the hot air rush out. You can literally feel the “driving force” of the hot air as it escapes. And, in your house, the greater the driving force, the faster you’ll lose the heat, which means your heating system has to work harder.

If there are cold spots on your wall, the warm air goes to those spots and heat is lost as long as the wall remains cold. In other words, you are going to keep losing heat until you fix the problems. If you take steps to make the wall warmer, such as caulking and installing insulation, the Delta T and the driving force are less.

Here’s something else to consider. In most cases, the warm air also contains moisture. When that warm air hits a cold spot, such as your window glass, it may well turn to water. It can do the same thing on or in your wall, causing mold or mildew to appear.

Well, I think you understand the problem, so what’s the solution? Simply stated, just caulk and insulate the wall and other locations to eliminate cold spots. I have learned through the years that cellulose or foam insulation is best for this purpose. Warming the wall will reduce the driving force by reducing the dreaded Delta T.

More Information:

Doug Rye, the “Doctor of Energy Efficiency-the King of Caulk and Talk” can be heard on several different Illinois radio stations. Or you can go to his Web site at, e-mail him at, or call 888-Doug-Rye or 501-653-7931. You can also sign up for a free newsletter and order his “how to” videotapes.


© 2016 Illinois Country Living Magazine.
Association of Illinois Electric Cooperatives

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