Energy Guy: Efficient insulation

Ive been accused of not being the most exciting guy. My wife would no doubt agree, and my granddaughter thinks Im outright boring. I do admit I tend to have a fairly narrow range of subjects that interest me. Good books, long walks and church potlucks come to mind. There is one thing that gets my heart pumping: Energy conservation!

Conserving energy for me is like being in the middle of a CSI episode. I work with people to gather evidence and fit together clues that lead to reducing bills, maintaining system integrity, and cleaning the environment. And every situation is different. Theres nothing boring about chasing energy robbers.

While there are many different culprits that cause us to be inefficient, one in particular seems to be difficult to understand and typically overlooked. Thats insulation. According to the U.S. Department of Energy, heating and cooling can account for up to 70 percent of the energy used in the average home. Lack of insulation is one of the leading causes of energy waste, so it is an important topic. Installing adequate insulation will save money and improve comfort.

Heat flows naturally via conduction, convection, and radiation from a warmer to a cooler space. Our homes lose heat in the winter and gain it in the summer. To maintain comfort, the heat lost in winter must be replaced by your heating system, and the heat gained in summer must be removed by your air conditioner. Insulation decreases your homes heating or cooling need by providing a resistance to heat loss or gain.

All materials resist the flow of heat to some extent. Even air slows heat movement. This, and blocking air infiltration, is why installing window plastic helps during winter. Insulation materials are rated on their ability to resist the flow of heat. This resistance is represented as an R-value. The higher the R-value, the greater the resistance to heat flow, and the better job the insulation will do at reducing your bills. The R-value of insulation depends on the type of material, its thickness, and its density.

The effectiveness of insulation depends on how its installed. Insulation which is compressed will not give you its full rated R-value. This can happen if you add denser insulation on top of lighter insulation, place something on top of the insulation, or when the insulation gets wet. It also happens if you place fiberglass blankets rated for one thickness into a thinner cavity, such as placing R-19 insulation intended for 6-inch wall cavity into a 3 1/2-inch wall cavity.

Joists, rafters, and studs have a different resistance to heat flow than does the insulation between. So, the overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself. This uneven heat flow across an area is called thermal bridging. Its important that attic insulation cover the tops of the joists and that insulating sheathing is used on walls.

Fiberglass blankets, loose fill cellulose, and low-density foams such as polyicynene and expanded polystyrene all work by limiting air movement. Still air is an effective insulator because it eliminates convection and has low conduction. This is why insulation works best when not compressed. Some foam insulation products such as polyisocyanurate, polyurethane, and extruded polystyrene are filled with special gases that provide additional resistance to heat flow.

So, which kind of insulation is best? Well, it depends. Basically, the type of insulation to buy and install depends on how much is needed, the accessibility of the space to be insulated, the amount space available for the insulation, the local availability and price of insulation, and homeowner preferences. And not all insulation materials are created the same in terms of R-value. For instance, fiberglass blankets have an R-value of about 3.3 per inch, polystyrene foam board about 3.5 per inch, icynene spray foam about 3.6 per inch, cellulose blow-in about 3.7 per inch, and urethane foam about 5.3 per inch.

The amount of energy you save depends on the climate, the type of insulation you use, and the living habits of your family. Installing any amount of insulation will save energy. However, after a certain amount there is a diminishing return on investment. In Ames (weather zone 5), the Department of Energy recommends an R-value of 38 for ceilings, 20 for walls, and 10 for basement walls, slabs, and crawl spaces. It makes economic sense for a homeowner to reach these numbers by adding insulation. Adding more than this will certainly save additional energy, but the economics are less attractive. These upgrades will provide smaller savings and a longer payback.

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Energy Guy: Efficient insulation