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Sweden adopted strict energy conservation measures after the first oil crisis in 1973 and has been strengthening them ever since. Features like R-33 walls and R-5 windows are now common. Along with energy-efficiency standards, however, have come problems. Sweden experienced a spate of "sick building syndrome" claims in the late 1970s. Government sponsored researchers have responded by identifying toxins in building materials and alternative products. They have also found correlations between chemical sensitivity and humidity levels in buildings. But the majority of their work has centered on improving ventilation systems. How Much Is Enough? In this country, ASHRAE currently recommends ventilating homes at a rate of .35 air changes per hour (ACH). Based on their long experience grappling with airquality concerns, however, the Swedes require more ventilation. Current