Is your house too hot? Too cold? To make it just right, insulation is a cost-effective, easy way to maximize the performance of your heating and cooling equipment, which means you'll save energy-and money. André Omer Desjarlais of the Department of Energy's Oak Ridge National Laboratory helped create an insulation fact sheet for the DOE. He maintains that any insulation is good. "Since we don't have any common ground rules for what's environmentally friendly, the real test is: Does the product take more energy to produce than it saves? And with insulation, they all save much more energy than they take to manufacture."

But you'll need to know a few things before you start calculating R-values. The first thing to know, of course is what R-values are. Here's what the pros say:

- Insulation is measured in R-value, which indicates the resistance to heat loss. You should speak in R-value when talking to a contractor. The DOE reminds readers that R-values are determined by material type, thickness, and installed weight per square foot, not by thickness alone. So don't be surprised to get different quotes from contractors for the same job.

- The higher the R-value, the greater the resistance to heat loss. For walls, you might see recommended R-values ranging from 13 to 23. In attics, R-values might be as low as 19 or as high as 60. Since insulation is very cost-effective, the price differential to upgrade your R-value isn't huge. The difference in the comfort of your home, however, can be large.

- Desjarlais recommends calculating your specific insulation needs, since some northern parts of the country require up to 25 inches, while some homes in the south might only need about 15. In addition, different insulating materials will result in different R-values. "Twenty inches of fiberglass has a different R-value than 20 inches of foam plastic," explains Desjarlais. You can calculate your R-value needs with the DOE's ZIP code calculator.

- You can also make a quick determination of how much insulation you need. As a guideline, manufacturer Johns Manville recommends 19 inches of loose-fill or blanket insulation. Scott DeShetler, Johns Manville's director of marketing communications, explains that you can measure how much insulation you already have by using a ruler; if you measure 19 inches, fine. If you have less than that, you should consider adding more. While 19 inches might be too much for some regions of the country, it's a good number to go by to keep things simple.

- Look for air leaks to the outside just by feeling around for them. Dirt streaks on your insulation are another sign of leakage. You should use mastic to permanently seal up any holes. (Don't use duct tape; it degrades over time and your leaks will return.) It's important to seal up leaks before adding attic insulation because after you insulate the holes may be hidden or less accessible.

- The DOE suggests that you should obtain cost estimates from several contractors for a stated R-value, and you should describe your job in writing in the same way for each contractor. The DOE says you should consider asking each contractor about air-sealing services as well.

- When it comes time to select an insulation contractor, you can peruse the Insulation Contractors of America website to search for a dependable contractor in your area. DeShetler suggests selecting two or three contractors to talk to. And he says to always get references: "Some contractors strictly do new construction. They'll think they can handle your house, but retrofit is different."

- In order to check that the right amount of insulation has been installed in your residence, the DOE says you should ask your contractor to attach vertical rulers to the joists prior to a loose-fill installation in your attic to help you see that the proper depth was installed. Desjarlais says this is a fairly common request. "Every insulation bag sold to the homeowner will have a table-a coverage chart-and on that table, it will tell how many inches a homeowner needs to get to a certain R-value. Having asked the contractor to put the rulers in, check to make sure the appropriate amount was installed to reach the desired R-value. You want to get what you paid for."

- According to Desjarlais, the most cost-effective and commonly found types of insulation are made from fiberglass and cellulose. Other materials include plastic foam, rigid insulation board, and mineral wool.

- To preserve or improve indoor air quality, ask about formaldehyde-free insulation.

- Desjarlais also says asbestos shouldn't be a concern in any new products, and in a retrofit, a trained professional should be able to spot any problems which might exist in homes built before the 1960s.

- You'll want to be familiar with the different styles of insulation. The Department of Energy gives a guide to the four basic forms of thermal insulation: blankets (batts or rolls), loose fill (blown-in cellulose or foam), rigid insulation, and reflective insulation systems. The DOE chart explains the method of installation for each type, where they are usually applied, and the advantages of each. This information will also be very useful in evaluating your insulation contractor's bid.

- Insulation application should be done in the attic first, since that's where the majority of heat loss happens. In an older home, you might add insulation to the walls. DeShetler says that this is generally unnecessary in homes built after the mid-'70s, because the insulation was widely used by then.

- The cost to retrofit a home with insulation can range from $500 for a smaller job to $2,000 for an older home.

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