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Today's builders, seeking to save energy, are building homes significantly tighter than those built 20 or even 10 years ago. This is admirable. But too often neither builder nor owner recognizes that these tight homes need controlled ventilation. Historically, natural air leakage (infiltration) has ventilated our homes and controlled moisture levels, odors, and indoor air pollutants. The tradeoff has been that we've had to accept cold drafts and excessive heat loss. To get the best of both worlds, we need tight houses that have controlled ventilation systems, so that we, and not the weather, determine where, when, and how much ventilation occurs. How Much Ventilation Is Enough? ASHRAE publishes ventilation standards based on house volume, but requiring no less than 15 cfm air change per hour per person. But because