Beginning this year, many namebrand windows will have lower Rvalue ratings. Eight window manufacturers —Andersen, Marvin, Pella, Louisiana-Pacific, BuiltBest, Norco, Sealrite, and Sembling- Mink—have adopted a new method of calculating R-values which will result in lower numbers. But the windows have not changed, only the calculations. The eight companies who have adopted the new method are all members of the National Wood Window and Door Association (NWWDA). According to Jim Benney, manager of technical services and spokesman for the NWWDA, the members elected to adopt the new method "so buyers would have a fair basis of comparison." The decision was initiated by a change in the 1989 ASHRAE Handbook which includes the new method in their procedures. NWWDA expects all window manufacturers to follow suit eventually. The new
