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Come fall, homeowners want information on furnaces, insulation and windows. Insulation seems the simplest, but is probably the most confusing.
Last week I wrote about federal energy tax credits. This week I want to clear up some of the confusion about insulation.
Heat naturally flows from a warmer area to a colder area. So when we heat a house (warmer area), the heat wants to go outside (colder area).
Since heating our homes is expensive, we try to keep the heat in the house. Materials used to stop the flow of heat are called insulation. The effectiveness of the material at stopping the flow of heat is defined as its R-factor. The R-factor is defined as "resistance to heat flow."
Everything has an R-value. Wikipedia has a good list in its section on R-value (insulation). Colorado Energy has an excellent listing on the web at www.coloradoenergy.org/procorner/stuff/r-values.htm.
R-value is usually quoted per inch. Products such as insulation batts are quoted by the R-value of the specified product. Be warned. The sites do not agree on the R-value of all materials. Everybody generalizes. Everybody rounds off.
Still air has an R-value of R-5 (per inch), add air current and it drops to R-1. Snow also has an R-1 value.
When kids make a fort out of cardboard boxes the cardboard has an R-value of 3 or 4. If dad makes his fort out of 1/2 -inch plywood the R-value is only 0.63.
Much of what we think of as strong has little insulation value. Poured concrete is only R-0.08 per inch. An entire 12-inch concrete block is only R-1.28. Common brick is only R-0.8.
A single-pane window is R-0.91. Add a storm window and you get R-2. The R-value of double-insulated windows depends upon the amount of air between the panes. A 3/16 -inch air space is R-1.61; 1/2 -inch air space is R-2.04; and 3/4 -inch air space is R-2.38. Add 0.20 Low E to the 1/2 -inch air space window to get R-3.13. Triple-pane glass with 1/4 -inch air spaces is R-2.56 and 1/2 -inch airspaces are R-3.23.
The R-values or comparative insulation products are pretty close. According to Colorado Energy, fiberglass batts can range from R-2.2 to R-3.85. High-density fiberglass batts range from R-3.6 to R-5. Rock and slag wool loose fill range from R-2.0 to R-3.3.
Attic-blown fiberglass is R-2.2. Wall-blown fiberglass is to R-3.2. Attic-blown cellulose, the big competitor of fiberglass, is R-3.13. Wall-blown cellulose is R-3.7.
I got in trouble in a recent article when I said that cellulose "seals" air spaces. It doesn't. According to researchers at Kansas State University, it "minimizes air movement." The U. S. Department of Energy calls it "infiltration" or "exfiltration" depending upon which way the heat path is being measured. Whatever you call it, it slows down heat loss and saves money.
In a University of Colorado study two side-by-side houses were studied. One had the attic and walls insulated with fiberglass, one with cellulose. After insulation the cellulose insulated house was 36 to 38 percent tighter and used 26.4 percent less energy to heat than the fiberglass insulated house. The Cellulose Insulation Manufacturers Association ( www.cellulose.org) promotes this study. The fiberglass folks do not.
Comparing the R-values of batt and blown products is not easy. Blown cellulose and fiberglass get into every nook and cranny. Batt fiberglass comes in standard widths and has to be cut around attic penetrations such as pipes.
Small gaps have dramatic effects on R-value according to KSU's "Residential Insulation" report. If as little as 1 to 2 percent of the insulated area is not filled there can be a 25 to 40 percent loss in R-value. At the same time, a contractor can "fluff" blown insulation and make it seem that you are getting more R-value than you really are.
KSU research indicates that the "performance of fiberglass degrades in cold weather due to convective air movement. Adding a 'cap' of blown cellulose reduces this phenomena."
Sprayed foam insulation is becoming a bigger factor. According to Wikipedia, icynene spray is rated at R-3.6 (loose-fill icynene: R-4). Phenolic-spray foam is R-4.8 to R-7. Open-cell polyurethane spray foam is R-3.6. Closed-cell is R-5.5 to R-6.5.
Foam insulation often has a higher R-value than equal thicknesses of cellulose or fiberglass. It is also more expensive. Usually a homeowner chooses foam to maximize the R-value in a limited space or to convert from the cold roof to hot roof theory of insulation and needs to stop attic air infiltration.
I hope this helps you to understand insulation and R-value better. As the cost of energy increases, we have to increase the insulation in our homes. Learn all you can. The more insulation you buy, the more you save.
Note: This article was accurate at the date of publication. However, information contained in it may have changed.
If you plan to use the information contained herein for any purpose, verification of its continued accuracy is your responsibility.