By Kris Wendtland
When the weather’s brisk, it’s smart to wear a coat. Your home needs the same kind of protection, too—insulation to keep cold air out and warm air in. Just as a coat closet features thin jackets for fall and heavy jackets for winter, different types of insulation, ranked by R-value, exist to keep your home comfortable and your electric bills affordable.
R-value reflects the ability of insulation and other parts of your home, like windows, to resist the transfer of heat. The rating depends on material, thickness, and density, and a higher R-value indicates more effective insulation. Multiple layers of insulation may be combined for a higher cumulative R-value.
How Insulation Works
Metals and liquids easily transfer heat, making them bad insulators. Air, however, does not conduct heat, making it a strong insulator when isolated in small pockets.
Just as fur keeps animals warm, insulation holds heat in (or out) of a building. Fur is a collection of hair—tiny hollow cylinders. Air fills the cylinders and spaces in-between. The smaller the space for air in between the cylinders and the more spaces there are (longer hair equals more space), the greater the insulation.
Building insulation works on the same principle. Fiberglass insulation, for example, exists as a collection of hollow fiberglass cylinders.
Be careful to preserve the air—the bulk of your home’s protection—when installing insulation. When an installer squeezes 3 in. of insulation into a 1-in. space, critical air pockets are eliminated. For this reason, actual insulating R-values may not always match the label. Insulation must be installed correctly to maximize protection—and electric bill savings.
The Value of R-Values
The first layer of insulation pays for itself fastest, saving more than half of the energy dollars spent on heating or air conditioning. However, as more insulation is added, efficiency gains dwindle.
Boosting the R-value of a wall from 0 to R-10 cuts 90 percent of heat loss from one side of the wall to the other. This makes an immediate difference you can feel. Adding an additional layer of R-15 insulation (a total R-value of 25) only cuts another 6 percent of heat transmission. Further increasing insulation thickness from R-25 to R-35 helps only by a little more than 1 percent.
In some regions with several months of very cold winds, increasing attic insulation values from R-25 to R-35 or even R-50 can be worth the investment over the life of your home. In most seasonal climates, however, replacing single-pane windows saves more energy than adding insulation in your attic, floors, or walls (assuming R-25 to R-30 is common throughout the home).
A typical single-pane window boasts an R-value of 0.9. In contrast, a triple-glazed pane assembly with low-emissivity (low e) insulated coatings have an R-value of 8.3. Based on an electricity cost of 10 cents per kilowatt-hour (kWh), a home with 18 single-pane windows (4 square feet each) could waste $94.32 in unnecessary expense across three months (assuming 12 hours per day of a 40 degrees Fahrenheit indoor/outdoor temperature differential). A more efficient window assembly would cost $10.20 over the same time. After a year, savings from switching out the windows could surpass $300.
Energy auditors and electric cooperative staff are trained to discuss the pros and cons of energy efficiency upgrades. Owen Electric Cooperative also offers energy audits to reveal areas ready for improvement; to schedule an audit, call 800-372-7612.
Sources: Jim Herritage, CEM, Energy Auditors, Inc.; Residential Energy: Cost Savings and Comfort for Existing Buildings by John Krigger and Chris Dorsi; University of Tennessee at Knoxville Department of Ecology and Evolutionary Biology
Kris Wendtland writes on writes on energy efficiency issues for the National Rural Electric Cooperative Association, the Arlington, Va.-based service arm of the nation’s 900-plus consumer-owned, not-for-profit electric cooperatives.
